JP4286644B2 - Method for manufacturing semiconductor device - Google Patents

Description

  The present invention relates to a semiconductor device and a manufacturing method thereof, and more specifically to a semiconductor device represented by a thin film transistor and a manufacturing method thereof. The present invention also relates to a semiconductor device using a silicon thin film having crystallinity formed on a substrate such as a glass substrate or a quartz substrate, and a manufacturing method thereof. The present invention further relates to an insulated gate semiconductor device such as a thin film transistor. And a manufacturing method thereof.

  Conventionally, a thin film transistor using a silicon film is known. This is a technique for forming a thin film transistor using a silicon film formed on a glass substrate or a quartz substrate. A glass substrate or a quartz substrate is used as a substrate because the thin film transistor is used for an active matrix liquid crystal display. Conventionally, a thin film transistor has been formed using an amorphous silicon film (a-Si). However, in order to obtain higher performance, a silicon film having crystallinity (referred to as a “crystalline silicon film” as appropriate in this specification). Attempts have been made to fabricate thin film transistors.

  A thin film transistor using a crystalline silicon film can operate at a high speed of two digits or more as compared with a thin film transistor using an amorphous silicon film. Therefore, the peripheral drive circuit of the active matrix type liquid crystal display device which has been constituted by an external IC circuit so far can be formed on the glass substrate or the quartz substrate by the crystalline silicon film in the same manner as the active matrix circuit. it can. Such a configuration is very advantageous for downsizing of the entire apparatus and simplification of the manufacturing process, and also leads to a reduction in manufacturing cost.

  Conventionally, a crystalline silicon film is obtained by forming an amorphous silicon film by a plasma CVD method or a low pressure thermal CVD method and then crystallizing the film by heat treatment or laser light irradiation. However, in the case of heat treatment among these, crystallization is uneven, and it is difficult to obtain the necessary crystallinity over a wide area. In the case of laser light irradiation, high crystallinity can be partially obtained, but it is difficult to obtain a good annealing effect over a wide area. In this case, the irradiation of laser light under conditions that obtain particularly good crystallinity tends to be unstable.

  By the way, the present inventors first introduced a technique for introducing a metal element (for example, nickel) that promotes crystallization of silicon into an amorphous silicon film and obtaining a crystalline silicon film by a heat treatment at a temperature lower than that of the prior art. (JP-A-6-232059, JP-A-7-321339). According to these methods, the crystallization speed can be increased and not only can be crystallized in a short time, but also compared to the conventional crystallization method by heating alone or crystallization of an amorphous film only by laser light irradiation, High crystallinity can be obtained uniformly over a wide area, and the obtained crystalline silicon film has crystallinity that can withstand practical use.

  However, since the metal element introduced to promote the crystallization of silicon is contained in the surface or surface of the crystalline silicon film obtained by the above method, the control of the amount introduced is delicate. There is a problem in reproducibility and stability (electrical stability of the obtained device). In particular, due to the influence of the remaining metal element, there are problems such as a change in characteristics of the obtained semiconductor device over time and a large OFF value in the case of a thin film transistor. In other words, the metal element that promotes the crystallization of silicon plays a valuable and useful role in obtaining a crystalline silicon film. It becomes a negative factor to cause.

  As described above, the present inventors have introduced the above-mentioned various cases in the case of forming a crystalline silicon film by introducing a metal element (for example, nickel) that promotes crystallization of silicon into the amorphous silicon film and performing heat treatment. In order to solve the problem, many experiments and examinations were made from various fields, and the metal element contained in the crystalline silicon film and remaining there was identified by a specific and special technique. It has been found that it can be removed or reduced, and the present invention has been reached.

  By the way, for example, an active matrix liquid crystal display device is small and light, and can display a high-speed moving image with a small size. However, since the substrate constituting the liquid crystal display device has a restriction that it needs translucency, the type of the substrate is limited, and examples thereof include a plastic substrate, a glass substrate, and a quartz substrate.

  Among them, the plastic substrate lacks heat resistance, and the quartz substrate can withstand high temperatures such as about 1000 ° C., and further about 1100 ° C., but is extremely expensive, especially when the area is increased, It is more than 10 times the price of a glass substrate and lacks cost performance. Therefore, glass substrates are generally widely used for the reasons of heat resistance and economy.

  Currently, the performance required for liquid crystal display devices is increasing, and the demand for performance and characteristics required for thin film transistors (hereinafter referred to as TFTs as appropriate) used as switching elements of liquid crystal display devices is also increasing. Therefore, research for forming a crystalline silicon film having crystallinity on a glass substrate has been actively conducted. At present, in order to form a crystalline silicon film on a glass substrate, first, an amorphous silicon film is used. And a method of crystallizing by heating or a method of crystallizing by irradiating a laser beam.

  That is, although the heat-resistant temperature of the glass substrate depends on the type, it is usually about 600 ° C. or slightly higher than that. Therefore, in the step of forming the crystalline silicon film, A process that exceeds the heat-resistant temperature cannot be adopted. For this reason, conventionally, in order to form a crystalline silicon film on a glass substrate, a method of forming an amorphous silicon film by a plasma CVD method or a low pressure CVD method and heating it to a temperature not higher than the above-mentioned heat-resistant temperature to crystallize it. Is adopted. Further, according to the method of crystallizing a silicon film by irradiating a laser beam, it is possible to form a crystalline silicon film having excellent crystallinity on a glass substrate, and the laser beam is thermally applied to the glass substrate. Has the advantage of not causing any significant damage.

  However, the crystalline silicon film obtained by crystallizing the amorphous silicon film by the laser light irradiation has a large number of defects derived from dangling bonds or the like. Since these defects are factors that degrade the TFT characteristics, when a TFT is fabricated using such a crystalline silicon film, the defects at the interface between the active layer and the gate insulating film or the silicon in the active layer It is necessary to passivate defects in crystal grains and grain boundaries. In particular, the defect at the grain boundary is the largest factor that scatters the charge, but it is very difficult to passivate the defect at the grain boundary.

  On the other hand, when a TFT is manufactured on a quartz substrate, heat treatment at a high temperature such as about 1000 ° C. or about 1100 ° C. is possible, so that defects at the crystal grain boundaries of the crystalline silicon film are compensated with silicon. Is possible. On the other hand, when a TFT is produced on a glass substrate, it is difficult to perform a heat treatment at a high temperature. Defects at crystal grain boundaries of the crystalline silicon film are passivated with hydrogen.

  Further, the N-channel TFT exhibits a practical field effect mobility by performing hydrogen plasma treatment. On the other hand, the effect of the hydrogen plasma treatment is not so remarkable in the P-channel TFT. This is interpreted because the level caused by crystal defects is formed in a relatively shallow region below the conduction electron band. Although it is possible to compensate for defects at the grain boundaries of the crystalline silicon film by hydrogen plasma treatment, the hydrogen that compensates for the defects is easily released, so that the TFT treated with hydrogen plasma, particularly an N-channel TFT. The reliability over time is not stable. For example, if an N-channel TFT is energized for 48 hours in an atmosphere at a temperature of 90 ° C., the mobility will be halved.

  Further, although the crystalline silicon film obtained by irradiating the laser beam has good film quality, when the film thickness is 1000 angstroms or less, ridges (unevenness) are formed on the surface of the crystalline silicon film. That is, when a silicon film is irradiated with a laser beam, the silicon film is instantaneously melted and locally expands, and a ridge (on the surface of the obtained crystalline silicon film is relaxed in order to relieve internal stress caused by this expansion. Unevenness) is formed. The height difference of the ridge is about 1/2 to 1 times the film thickness. For example, when laser annealing is performed after heating and crystallizing an amorphous silicon film having a thickness of about 700 angstroms, a ridge having a height of about 100 to 300 angstroms is formed on the surface.

  In an insulated gate type semiconductor device, a potential barrier or trap level due to dangling bonds, lattice distortion, etc. is formed on the ridge on the surface of the crystalline silicon film, so that the interface between the active layer and the gate insulating film It will raise the level. In addition, since the top of the ridge is steep, the electric field tends to concentrate, so that it becomes a source of leakage current and ultimately causes breakdown. Further, the ridge on the surface of the crystalline silicon film impairs the coverage of the gate insulating film deposited by sputtering or CVD, and lowers the reliability such as insulation failure.

  In the present invention, a crystalline silicon film is formed on an amorphous silicon film by using a metal element that promotes crystallization of silicon, and the metal element in the crystalline silicon film thus obtained is removed or the It is an object to provide a new and extremely useful technique for reducing the concentration of metal elements.

  The present invention is also obtained by removing a metal element or reducing the concentration of the metal element from a crystalline silicon film obtained by using a metal element that promotes crystallization of silicon in an amorphous silicon film. Another object of the present invention is to provide a semiconductor device having high characteristics using a crystalline silicon film having high crystallinity and a manufacturing method thereof. A further object of the present invention is to provide a semiconductor device and a method for manufacturing the semiconductor device that can improve the characteristics and reliability of the semiconductor device thus obtained.

  In addition, the present invention solves the above-described problems, and a method for manufacturing a semiconductor device capable of passivating a defect in a crystal grain boundary of a silicon film crystallized from an amorphous silicon film without using a hydrogen plasma treatment The purpose is to provide. A further object of the present invention is to provide a method for manufacturing a semiconductor device having high reliability and high mobility. In particular, the present invention has a gate insulating film made of a deposited film, and improves the reliability and characteristics of a semiconductor device on a glass substrate. An object is to provide an improved semiconductor device and a manufacturing method thereof. In addition to the above, the present invention has an object corresponding to the configuration described below, and these will be appropriately supplemented and described in the following description.

  (1) In the present invention, a metal element that promotes crystallization of silicon is intentionally introduced into an amorphous silicon film, and the amorphous silicon film is crystallized by a first heat treatment to obtain a crystalline silicon film. A step of performing a second heat treatment in an oxidizing atmosphere to remove or reduce the metal element present in the crystalline silicon film, and a step of removing the thermal oxide film formed in the step And a step of forming a thermal oxide film on the surface of the region from which the thermal oxide film has been removed by re-thermal oxidation.

  (2) The present invention intentionally introduces a metal element that promotes crystallization of silicon into the amorphous silicon film, and crystallizes the amorphous silicon film by a first heat treatment, thereby forming a crystalline silicon film. And a second thermal oxidation treatment in an oxidizing atmosphere to form a thermal oxide film on the surface of the crystalline silicon film, and gettering the metal element into the thermal oxide film. Removing or reducing the metal element present in the silicon film; removing the thermal oxide film formed in the process; and re-thermally oxidizing the surface of the region from which the thermal oxide film has been removed by thermal oxidation. And a step of forming an oxide film. A method for manufacturing a semiconductor device is provided.

  (3) The present invention intentionally introduces a metal element that promotes crystallization of silicon into an amorphous silicon film, and crystallizes the amorphous silicon film by a first heat treatment to obtain a crystalline silicon film. A step of performing a second heat oxidation treatment in an oxidizing atmosphere to remove or reduce the metal element present in the crystalline silicon film, and a step of removing the thermal oxide film formed in the step And a step of forming an active layer of the thin film transistor by patterning, and a step of forming a thermal oxide film constituting at least a part of the gate insulating film on the surface of the active layer by thermal oxidation A method for manufacturing a device is provided.

  (4) The present invention includes a step of selectively introducing a metal element for promoting crystallization of silicon into an amorphous silicon film, and a film from a region where the metal element is selectively introduced by the first heat treatment. A step of performing crystal growth in a direction parallel to the step, a step of performing a second heat treatment in an oxidizing atmosphere to form a thermal oxide film on the surface of the region where the crystal growth has been performed, There is provided a method for manufacturing a semiconductor device, comprising: a step of removing; and a step of forming an active layer of the semiconductor device using a region from which the thermal oxide film has been removed.

  (5) The present invention includes a crystalline silicon film sandwiched between first and second oxide films, and the crystalline silicon film contains a metal element that promotes crystallization of silicon, and the crystal In the conductive silicon film, the metal element has a high concentration distribution in the vicinity of the interface with the first and / or second oxide film.

  (6) The present invention includes a base film made of an oxide film, a crystalline silicon film formed on the base film, and a thermal oxide film formed on the crystalline silicon film. The silicon film contains a metal element that promotes crystallization of silicon, and the metal element that promotes crystallization of silicon has a high concentration distribution in the vicinity of the interface with the base and / or the thermal oxide film. Provided is a semiconductor device in which an oxide film forms at least a part of a gate insulating film of a thin film transistor.

  (7) The present invention intentionally introduces a metal element that promotes crystallization of silicon into the amorphous silicon film, and crystallizes the amorphous silicon film by a first heat treatment, thereby forming a crystalline silicon film. A step of performing a second heat treatment in an oxidizing atmosphere containing a halogen element to remove or reduce the metal element present in the crystalline silicon film, and a heat formed in the step There is provided a method for manufacturing a semiconductor device, comprising: a step of removing an oxide film; and a step of forming a thermal oxide film by thermal oxidation again on the surface of the region from which the thermal oxide film has been removed.

  (8) The present invention intentionally introduces a metal element that promotes crystallization of silicon into an amorphous silicon film, and crystallizes the amorphous silicon film by a first heat treatment to obtain a crystalline silicon film. Performing a second heat oxidation treatment in an oxidizing atmosphere containing a halogen element, forming a thermal oxide film on the surface of the crystalline silicon film, and gettering the metal element to the thermal oxide film The step of removing or reducing the metal element present in the crystalline silicon film, the step of removing the thermal oxide film formed in the step, and the surface of the region where the thermal oxide film has been removed are performed again. And a method of forming a thermal oxide film by thermal oxidation.

  (9) In the present invention, a metal element that promotes crystallization of silicon is intentionally introduced into an amorphous silicon film, and the amorphous silicon film is crystallized by a first heat treatment to obtain a crystalline silicon film. A step of performing a second heat oxidation treatment in an oxidizing atmosphere containing a halogen element to remove or reduce the metal element present in the crystalline silicon film, and a thermal oxide film formed in the step A step of removing, forming a thin film transistor active layer by patterning, and forming a thermal oxide film constituting at least a part of the gate insulating film on the surface of the active layer by thermal oxidation. A method for manufacturing a semiconductor device is provided.

  (10) The present invention includes a step of selectively introducing a metal element for promoting crystallization of silicon into an amorphous silicon film, and a film from a region where the metal element is selectively introduced by the first heat treatment. And a step of forming a thermal oxide film on the surface of the region where the crystal growth is performed by performing a second heat treatment in an oxidizing atmosphere containing a halogen element. And a step of removing the thermal oxide film, and a step of forming an active layer of the semiconductor device using the region from which the thermal oxide film has been removed.

  (11) The present invention includes a crystalline silicon film sandwiched between first and second oxide films, and the crystalline silicon film contains hydrogen and a halogen element and promotes crystallization of silicon A semiconductor device characterized in that, in the crystalline silicon film, the metal element has a high concentration distribution in the vicinity of the interface with the first and / or second oxide film. provide.

  (12) The present invention includes a base film made of an oxide film, a crystalline silicon film formed on the base film, and a thermal oxide film formed on the crystalline silicon film. The silicon film contains metal elements that promote crystallization of silicon and hydrogen and halogen elements. The metal elements that promote crystallization of silicon have a high concentration distribution in the vicinity of the interface with the base and / or the thermal oxide film. And the halogen element has a high concentration distribution in the vicinity of the interface with the base and / or the thermal oxide film, and the thermal oxide film forms at least part of the gate insulating film of the thin film transistor. I will provide a.

  (13) In the present invention, a metal element that promotes crystallization of silicon is intentionally introduced into an amorphous silicon film, and the amorphous silicon film is crystallized by a first heat treatment to obtain a crystalline silicon film. A step of irradiating the crystalline silicon film with laser light or strong light, and a second heat treatment in an oxidizing atmosphere containing a halogen element to be present in the crystalline silicon film. Removing or reducing the metal element, removing the thermal oxide film formed in the process, and forming a thermal oxide film on the surface of the region from which the thermal oxide film has been removed by thermal oxidation again. A method for manufacturing a semiconductor device is provided.

  (14) In the present invention, a metal element for promoting crystallization of silicon is intentionally introduced into an amorphous silicon film, and the amorphous silicon film is crystallized by a first heat treatment to obtain a crystalline silicon film. A step of irradiating the crystalline silicon film with laser light or intense light to diffuse the metal element present in the crystalline silicon film in the crystalline silicon film, and a halogen element Performing a second heat treatment in an oxidizing atmosphere to getter the metal element present in the crystalline silicon film into the thermal oxide film to be formed; and the thermal oxide film formed in the step There is provided a method for manufacturing a semiconductor device, which includes a step of removing, and a step of forming a thermal oxide film again by thermal oxidation on a surface of a region where the thermal oxide film is removed.

  (15) The present invention intentionally and selectively introduces a metal element that promotes crystallization of silicon into an amorphous silicon film, and performs a first heat treatment on the amorphous silicon film, A step of crystal growth in a direction parallel to the film from the region where the metal element is intentionally and selectively introduced, and the metal present in the crystal growth region by irradiation with laser light or strong light A step of diffusing the element, and a step of performing a second heat treatment in an oxidizing atmosphere containing a halogen element to getter the metal element present in the crystal-grown region into the thermal oxide film to be formed And a step of removing the thermal oxide film formed in the step, and a step of forming a thermal oxide film on the surface of the region from which the thermal oxide film has been removed by re-thermal oxidation. A method for manufacturing a device is provided.

  (16) The present invention intentionally introduces a metal element that promotes crystallization of silicon into an amorphous silicon film, and crystallizes the amorphous silicon film by a first heat treatment to obtain a crystalline silicon film. A step of patterning the crystalline silicon film to form an active layer of a semiconductor device, a step of irradiating the active layer with laser light or strong light, and an oxidizing atmosphere containing a halogen element Performing a second heat treatment to remove or reduce the metal element present in the active layer, removing the thermal oxide film formed in the step, and applying heat again to the surface of the active layer. And a step of forming a thermal oxide film by oxidation. A method for manufacturing a semiconductor device is provided.

  (17) The present invention intentionally introduces a metal element that promotes crystallization of silicon into an amorphous silicon film, and crystallizes the amorphous silicon film by a first heat treatment, thereby forming a crystalline silicon film. A step of patterning the crystalline silicon film to form an active layer of a semiconductor device, a step of irradiating the active layer with laser light or strong light, and an oxidizing atmosphere containing a halogen element. And a step of removing or reducing the metal element present in the active layer by performing a second heat treatment, a step of removing the thermal oxide film formed in the step, Forming a thermal oxide film by thermal oxidation, wherein the active layer has a slanted shape with an angle formed between the side surface and the base surface of 20 ° to 50 °. I will provide a.

  (18) In the present invention, a crystalline silicon film is obtained by intentionally introducing a metal element that promotes crystallization of silicon into an amorphous silicon film and crystallizing the amorphous silicon film by a first heat treatment. A step of irradiating the crystalline silicon film with laser light or strong light, and a second heat treatment in an oxidizing atmosphere to remove the metal element present in the crystalline silicon film or A step of reducing, a step of removing the thermal oxide film formed in the step, and a step of forming a thermal oxide film on the surface of the region from which the thermal oxide film has been removed by thermal oxidation again. A method for manufacturing a semiconductor device is provided.

  (19) In the present invention, a metal element that promotes crystallization of silicon is intentionally introduced into an amorphous silicon film, and the amorphous silicon film is crystallized by a first heat treatment to obtain a crystalline silicon film. A step of irradiating the crystalline silicon film with laser light or strong light to diffuse the metal element present in the crystalline silicon film in the crystalline silicon film; and in an oxidizing atmosphere. Performing a second heat treatment to getter the metal element present in the crystalline silicon film into the thermal oxide film to be formed; and removing the thermal oxide film formed in the process; And a step of forming a thermal oxide film on the surface of the region from which the thermal oxide film has been removed by re-thermal oxidation.

  (20) The present invention intentionally and selectively introduces a metal element that promotes crystallization of silicon into the amorphous silicon film, and performs a first heat treatment on the amorphous silicon film, A step of crystal growth in a direction parallel to the film from the region where the metal element is intentionally and selectively introduced, and the metal present in the crystal growth region by irradiation with laser light or strong light A step of diffusing the element, a second heat treatment in an oxidizing atmosphere, and a step of gettering the metal element present in the crystal-grown region in the thermal oxide film to be formed; A method for manufacturing a semiconductor device, comprising: a step of removing a formed thermal oxide film; and a step of forming a thermal oxide film by re-thermal oxidation on a surface of a region from which the thermal oxide film has been removed. provide.

  (21) The present invention intentionally introduces a metal element that promotes crystallization of silicon into an amorphous silicon film, and crystallizes the amorphous silicon film by a first heat treatment to obtain a crystalline silicon film. A step of patterning the crystalline silicon film to form an active layer of a semiconductor device, a step of irradiating the active layer with laser light or strong light, and a second heating in an oxidizing atmosphere. Performing a treatment to remove or reduce the metal element present in the active layer, removing a thermal oxide film formed in the step, and thermally oxidizing the surface of the active layer by thermal oxidation again. A method for manufacturing a semiconductor device, comprising: forming a film.

  (22) In the present invention, a crystalline silicon film is obtained by intentionally introducing a metal element that promotes crystallization of silicon into an amorphous silicon film and crystallizing the amorphous silicon film by a first heat treatment. A step of patterning the crystalline silicon film to form an active layer of a semiconductor device, a step of irradiating the active layer with laser light or strong light, and a second heating in an oxidizing atmosphere. Performing a treatment to remove or reduce the metal element present in the active layer, removing a thermal oxide film formed in the step, and thermally oxidizing the surface of the active layer by thermal oxidation again. And providing a method for manufacturing a semiconductor device, wherein the active layer has an inclined shape whose side surface makes an angle of 20 ° to 50 ° with the base surface.

  (23) The present invention includes a step of forming an amorphous silicon film on a substrate having an insulating surface, a step of intentionally introducing a metal element that promotes crystallization of silicon into the amorphous silicon film, and a temperature. A step of crystallizing the amorphous silicon film by a first heat treatment at 750 ° C. to 1100 ° C. to obtain a crystalline silicon film, and a step of patterning the crystalline silicon film to form an active layer of a semiconductor device; A step of removing or reducing the metal element present in the active layer by performing a second heat treatment in an oxidizing atmosphere containing a halogen element, and a step of removing the thermal oxide film formed in the step And a step of forming a thermal oxide film by thermal oxidation again after removing the thermal oxide film, wherein the temperature of the second heat treatment is higher than the temperature of the first heat treatment. A method for manufacturing a semiconductor device is provided.

  (24) The present invention includes a step of forming an amorphous silicon film on a substrate having an insulating surface, a step of intentionally introducing a metal element that promotes crystallization of silicon into the amorphous silicon film, and a temperature. A step of crystallizing the amorphous silicon film by a first heat treatment at 750 ° C. to 1100 ° C. to obtain a crystalline silicon film, and a step of patterning the crystalline silicon film to form an active layer of a semiconductor device; A step of performing a second heat treatment in an oxidizing atmosphere containing a halogen element to getter the metal element present in the active layer into a thermal oxide film to be formed; And removing the thermal oxide film, and forming the thermal oxide film by thermal oxidation again after removing the thermal oxide film, and the temperature of the second heat treatment is the first heating temperature. A method for manufacturing a semiconductor device, characterized by being higher than a processing temperature. Subjected to.

  (25) The present invention includes a step of forming an amorphous silicon film on a substrate having an insulating surface, and a step of intentionally and selectively introducing a metal element that promotes crystallization of silicon into the amorphous silicon film. And a step of crystal growth in a direction parallel to the film from a region where the metal element of the amorphous silicon film is intentionally and selectively introduced by a first heat treatment at a temperature of 750 ° C. to 1100 ° C. A step of forming an active layer of a semiconductor device using a region that has been crystallized in a direction parallel to the film by patterning, and a second heat treatment is performed in an oxidizing atmosphere containing a halogen element. A step of gettering the metal element present in the thermal oxide film to be formed; a step of removing the thermal oxide film formed in the step; and thermal oxidation again after removing the thermal oxide film And a step of forming a thermal oxide film by Temperature of the second heat treatment to provide a method for manufacturing a semiconductor device, wherein the higher than the temperature of the first heat treatment.

  (26) The present invention performs a step of forming an amorphous silicon film, a step of holding a metal element that promotes crystallization of silicon in contact with the surface of the amorphous silicon film, and a first heat treatment Crystallizing the amorphous silicon film to obtain a crystalline silicon film, and performing a second heat treatment at a temperature of 500 ° C. to 700 ° C. in an atmosphere containing oxygen, hydrogen and fluorine Provided is a method for manufacturing a semiconductor device, which includes a step of forming a thermal oxide film on a surface of a film and a step of removing the thermal oxide film.

  (27) The present invention performs a step of forming an amorphous silicon film, a step of holding a metal element that promotes crystallization of silicon in contact with the surface of the amorphous silicon film, and a first heat treatment Crystallizing the amorphous silicon film to obtain a crystalline silicon film, and performing a second heat treatment at a temperature of 500 ° C. to 700 ° C. in an atmosphere containing oxygen, hydrogen, fluorine and chlorine There is provided a method for manufacturing a semiconductor device, characterized by comprising a step of forming a thermal oxide film on the surface of a conductive silicon film and a step of removing the thermal oxide film.

  (28) The present invention includes a step of forming an amorphous silicon film, a step of holding a metal element for promoting crystallization of silicon in contact with the surface of the amorphous silicon film, and a heat treatment to perform the amorphous process. A step of crystallizing a crystalline silicon film to obtain a crystalline silicon film, a step of forming a wet oxide film on the surface of the crystalline silicon film in an atmosphere containing fluorine and / or chlorine, and a step of removing the oxide film A method for manufacturing a semiconductor device is provided.

(29) The present invention is a semiconductor device having a silicon film having crystallinity, and a metal element that promotes crystallization of silicon is 1 × 10 ¹⁶ cm ^{−3 to} 5 × 10 ¹⁸ cm ^{− in the} silicon film. ^{3 with} a concentration of fluorine atoms of 1 × 10 ¹⁵ cm ⁻³ to 1 × 10 ²⁰ cm ⁻³ and hydrogen atoms of 1 × 10 ¹⁷ cm ⁻³ to 1 × 10 ²¹ cm ⁻³ . Provided is a semiconductor device characterized by being contained in a concentration. The concentration unit “... Cm ⁻³ ” means the number of atoms per cubic centimeter (atoms / cm ³ ), and this is the same in this specification.

  (30) The present invention includes a step of forming an amorphous silicon film, a step of crystallizing the amorphous silicon film to form a crystalline silicon film, and heating in an oxidizing atmosphere to which a fluorine compound gas is added. Then, a step of growing a thermal oxide film on the surface of the crystalline silicon film, a step of removing the thermal oxide film on the surface of the crystalline silicon film, and a step of depositing an insulating film on the surface of the crystalline silicon film A method for manufacturing a semiconductor device is provided.

  (31) In the present invention, a step of forming an amorphous silicon film, a step of irradiating a laser beam to crystallize the amorphous silicon film to form a crystalline silicon film, and a fluorine compound gas are added. Heating in an oxidizing atmosphere to grow a thermal oxide film on the surface of the crystalline silicon film, removing the thermal oxide film on the surface of the crystalline silicon film, and insulating the surface of the crystalline silicon film A method of manufacturing a semiconductor device, comprising: depositing a film.

  (32) The present invention relates to a method of forming a thin film transistor over a substrate having an insulating surface, a step of forming an amorphous silicon film, and a step of crystallizing the amorphous silicon film to form a crystalline silicon film. Heating in an oxidizing atmosphere to which a fluorine compound gas is added to grow a thermal oxide film on the surface of the crystalline silicon film; removing the thermal oxide film on the surface of the crystalline silicon film; Shaping the crystalline silicon film to form an active layer of the thin film transistor; depositing an insulating film on the surface of the active layer to form a gate insulating film on at least the surface of the channel region; and Forming a gate electrode on the surface of the film, and implanting impurity ions imparting a conductivity type into the active layer using the gate electrode as a mask to form a source and a drain in a self-aligned manner. Features To provide a method for manufacturing a semiconductor device to be.

  (33) The present invention provides a method for forming a thin film transistor over a substrate having an insulating surface, a step of forming an amorphous silicon film, a step of crystallizing the amorphous silicon film to form a crystalline silicon film, Irradiating the crystalline silicon film with laser light, heating in an oxidizing atmosphere to which a fluorine compound gas is added, and growing a thermal oxide film on the surface of the crystalline silicon film; and Removing the thermal oxide film on the surface of the film, shaping the crystalline silicon film to form an active layer of the thin film transistor, and depositing an insulating film on the surface of the active layer to form at least the surface of the channel region A step of forming a gate insulating film; a step of forming a gate electrode on the surface of the gate insulating film; and implanting impurity ions imparting conductivity type to the active layer using the gate electrode as a mask, The self There is provided a method for manufacturing a semiconductor device characterized by comprising the step of coupling formed.

  As described above, according to the present invention, the metal in the crystalline silicon film obtained by using the metal element that promotes the crystallization of silicon can be removed, and the concentration thereof can be reduced. A silicon film having excellent crystallinity can be obtained by kettering the metal in an oxidizing atmosphere, particularly an oxidizing atmosphere to which halogen is added. Further, a thin film semiconductor device having higher reliability and superior performance can be obtained by using these crystalline silicon films.

  In the method for manufacturing a semiconductor device according to the present invention, a thermal oxide film is grown in an oxidizing atmosphere to which fluorine is added, so that the temperature is below the strain point of the glass substrate for several hours to several tens. By heating for a period of time, it is possible to grow a thermal oxide film to a film thickness of several hundred angstroms. Further, by growing the thermal oxide film, surplus Si is generated, and defects in the crystal grain boundary of the crystalline silicon film can be passivated with Si, so that hydrogen plasma treatment can be eliminated. .

  Furthermore, since the surface of the crystalline silicon film can be flattened by a thermal oxidation process, the gate insulating film made of a deposited film can be used even if a process of obtaining a crystalline silicon film by irradiating a laser beam is adopted. Can be formed with good coverage. For this reason, the interface state between the gate insulating film and the active layer can be lowered. Further, since the crystalline silicon film obtained by laser irradiation is excellent in crystallinity, the mobility of the semiconductor device can be further improved. Therefore, an insulating gate type semiconductor device such as a high mobility and high reliability TFT can be manufactured on a substrate that is difficult to process at a high temperature such as about 1000 ° C., such as a glass substrate.

  In a typical embodiment of the present invention, first, a metal element that promotes crystallization of silicon is introduced into the surface of a previously formed amorphous silicon film, and a crystalline silicon film is formed using the metal element. To do. Next, by forming a thermal oxide film on the surface of the crystalline silicon film, the metal element is transferred or gettered into the thermal oxide film, and the concentration of the metal element in the crystalline silicon film is reduced or The metal element is removed.

  The amorphous silicon film can be formed by a plasma CVD method, a low pressure thermal CVD method, or any other appropriate method. The amorphous silicon film is formed on an appropriate solid surface, but is formed on a substrate when configured as a semiconductor device. The substrate is not particularly limited, and a glass substrate, a quartz substrate, a ceramic substrate, and other substrates are used. The amorphous silicon film is also formed on a film such as a silicon oxide film formed on the surface of the substrate, but the substrate in this specification includes these cases. Meaning.

  Next, a metal element for promoting crystallization of silicon is introduced into the surface of the amorphous silicon film formed in advance as described above. The metal elements that promote the crystallization of silicon include iron (Fe), nickel (Ni), cobalt (Co), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir ), Platinum (Pt), copper (Cu), and gold (Au), or one or more kinds of metal elements. These metal elements are metal elements that are used as metal elements that promote crystallization of silicon in any of the inventions described in this specification. The metal element that promotes the crystallization of silicon.

  The locations where these metal elements are introduced include (a) the entire surface of the amorphous silicon film, and (b) a slit-like surface at an appropriate location on the film surface of the amorphous silicon film (in this embodiment, preferably amorphous) A slit-like opening is provided on the surface of the silicon film), and (c) an end of the surface of the amorphous silicon film (for example, if the film surface of the amorphous silicon film is a rectangular surface) One end, two ends, three ends or four ends, or the peripheral portion of the amorphous silicon film if the film surface is a circular surface, etc.), (d) amorphous There is no particular limitation such as the center of the surface of the porous silicon film, (e) dots (that is, dots with a predetermined interval on the film surface of the amorphous silicon film), and preferably (a) to ( It is introduced in the form of b).

  There is no particular limitation on the size of the slit-shaped opening in the mode of introducing the slit-shaped surface in the mode of (A) above. For example, as a method of introduction, a metal salt solution is applied as follows. In the embodiment, depending on the wettability and fluidity of the solution, the width can be, for example, 20 μm or more. Further, the length in the longitudinal direction may be arbitrarily determined, and for example, it may be in the range of about several tens of μm to 30 cm. Moreover, the aspect which introduce | transduces the said metal element into the back surface of an amorphous silicon film | membrane is also taken, and it can also introduce | transduce into the front and back both surfaces.

  Further, the method for introducing these metal elements into the amorphous silicon film is not particularly limited as long as it is a technique capable of allowing the metal elements to exist on the surface of the amorphous silicon film or inside thereof, for example, a sputtering method. The CVD method, the plasma treatment method (including the plasma CVD method), the adsorption method, and the method of applying a metal salt solution can be used. Among these, the method using a solution is simple and useful in that the concentration of the metal element can be easily adjusted. As the metal salt, various salts can be used, and as the solvent, water, alcohols, aldehydes, ethers and other organic solvents, or a mixed solvent of water and an organic solvent can be used. The solution is not necessarily a solution in which the salt is completely dissolved, and may be a solution in which a part or all of the metal salt is present in a suspended state.

  As for the type of metal salt, any organic salt or inorganic salt can be used as long as it can exist as a solution or suspension as described above. For example, ferrous bromide, ferric bromide, ferric acetate, ferrous chloride, ferrous chloride, ferric fluoride, ferric nitrate, ferrous phosphate And ferric phosphate, and cobalt salts include cobalt bromide, cobalt acetate, cobalt chloride, cobalt fluoride, and cobalt nitrate.

  Nickel salts include nickel bromide, nickel acetate, nickel oxalate, nickel carbonate, nickel chloride, nickel iodide, nickel nitrate, nickel sulfate, nickel formate, nickel oxide, nickel hydroxide, nickel acetyl acetate, 4-cyclohexyl Examples thereof include nickel butyrate and nickel 2-ethylhexanoate. Examples of ruthenium salts include ruthenium chloride, examples of rhodium salts include rhodium chloride, examples of palladium salts include palladium chloride and the like, examples of osmium salts include osmium chloride, and examples of iridium salts. Examples of platinum salts include iridium trichloride and iridium tetrachloride. Examples of platinum salts include cupric chloride. Examples of copper salts include cupric acetate, cupric chloride, and cupric nitrate. Examples include gold trichloride, gold chloride and the like.

  After introducing a metal element into the amorphous silicon film as described above, a crystalline silicon film is formed using the metal element. This crystallization is performed by heat treatment (thermal crystallization: Solid Phase Crystallization), irradiation with intense light such as laser light, ultraviolet light, infrared light, or the like, and heat treatment is preferably used. In the case of heat treatment, laser light irradiation or strong light irradiation may be performed thereafter. This thermal crystallization proceeds even in an atmosphere containing hydrogen or oxygen as a heating atmosphere, but an inert atmosphere such as nitrogen or argon is preferably used. In addition, this heat treatment or this heat treatment temperature is appropriately referred to as “first heat treatment” or “first heat treatment temperature” in this specification.

  The first heat treatment can be performed in a temperature range of about 450 to 1100 ° C., and preferably in a range of about 550 to 1050 ° C. Crystallization proceeds even at a temperature of about 400 ° C. However, in this case, since the crystallization rate is slow and a long time is required, the temperature is about 450 ° C. or higher, preferably about 550 ° C. or higher. When a heat resistant substrate such as a quartz substrate is used as the substrate, the temperature is preferably 700 ° C. or higher, more preferably 750 ° C. or higher. If the heat treatment temperature is higher, higher quality crystals can be obtained, and the crystallization rate can be increased.

  For example, when a glass substrate having a strain point of 667 ° C. is used as the substrate, the first heating temperature is limited to about 600 to 650 ° C. in relation to the strain point, but may be a glass substrate with higher heat resistance. Of course, the temperature may be higher. In the case of a quartz substrate, it can be applied up to about 1100 ° C., but is preferably about 1050 ° C. or less. This is because if the temperature exceeds about 1050 ° C., the jig made of quartz is distorted or a burden is imposed on the apparatus. In this sense, the temperature is preferably 980 ° C. or lower. However, when a more heat-resistant jig is used, it can be performed even at about 1100 ° C. Further, after this heat treatment, irradiation with laser light or irradiation with strong light such as infrared rays or ultraviolet rays can be performed.

  Next, a thermal oxide film is formed on the surface of the crystalline silicon film. In the present invention, this makes it possible to transfer or getter the metal element into the thermal oxide film, to reduce the concentration of the metal element in the crystalline silicon film, or to remove the metal element. An oxidizing atmosphere is used to form the thermal oxide film, and preferred embodiments thereof include (f) an oxygen atmosphere, (g) an oxygen-containing atmosphere, and (g) a compound that releases oxygen at the temperature at which the thermal oxide film is formed. , An atmosphere containing (halogen), an atmosphere containing oxygen and halogen of (v) and (f) to (c), and the like.

  The thermal oxide film can be formed in the same range as the temperature applied in the thermal crystallization, that is, in the range of about 450 to 1100 ° C., preferably in the range of about 700 to 1050 ° C., more preferably about 800. It can carry out in the range of -1050 degreeC. This temperature can be about the same as the temperature applied in the thermal crystallization (first heat treatment temperature), but is preferably higher than the temperature applied in the thermal crystallization. As a result, a thermal oxide film is formed, and thermal crystallization can be further advanced as compared with the case where the thermal oxide film is formed at a temperature similar to the first heat treatment temperature.

  Thus, a thermal oxide film is formed on the surface of the crystalline silicon film. At this time, the metal element is gettered in the thermal oxide film by the action of oxygen in the oxidizing atmosphere, the action of halogen, or the action of oxygen and halogen. The concentration of the metal element in the crystalline silicon film is lowered or the metal element is removed. Further, the crystallinity of the crystalline silicon film is improved in accordance with the formation of the thermal oxide film. Note that the heat treatment for forming the thermal oxide film or the temperature thereof is appropriately referred to as “second heat treatment temperature” or “second heat treatment temperature” in this specification.

  Next, the thermal oxide film gettered with the metal element is removed. The method for removing the thermal oxide film is not particularly limited as long as it is a method capable of removing the thermal oxide film. For example, it can be performed using buffer hydrofluoric acid or other hydrofluoric acid-based etchants. Thus, a crystalline silicon film having high crystallinity and from which the metal element is removed or the concentration of the metal element is low can be obtained. This crystalline silicon film has excellent characteristics as various elements in a semiconductor device, and particularly has extremely excellent characteristics as an active layer thereof.

  1 to 4 are photomicrographs of several examples of crystalline silicon films obtained by the present invention. 1 to 2 are magnified photographs at a magnification of 450 times with an optical microscope, FIG. 3 is a magnified photograph at a magnification of 50000 times (50,000 times) with a transmission electron microscope (TEM), and FIG. 4 is a magnification with a transmission electron microscope. It is an enlarged photograph of 250,000 times (250,000 times).

  Among these, FIG. 1 shows a crystalline silicon film obtained by introducing and applying nickel element to one end of a rectangular amorphous silicon film, and crystallizing it. FIG. 2 shows the nickel element in an amorphous silicon film. Is a crystalline silicon film obtained by being introduced and applied to the entire surface of the film and crystallized. As is apparent from the photograph of FIG. 1, it can be seen that the crystal grows in parallel or almost in parallel from one end to the other end. Further, in the photograph of FIG. 2, which is a case where nickel element is grown on the entire surface of the amorphous silicon film, star-like shading is seen, and the crystal grows radially around many points. I understand that.

  Next, FIGS. 3 to 4 are enlarged photographs taken with a transmission electron microscope. The crystalline silicon films shown in FIGS. 3 to 4 are generally obtained in the following steps (A) to (G). (These steps are similar to those of Example 21 described later). These steps (A) to (G) are schematically shown in FIG.

  (A) A quartz substrate having a sufficiently smooth plane was washed, and an amorphous silicon film was formed on its surface to a thickness of 500 angstroms by low pressure thermal CVD (LPCVD). (B) Next, a silicon oxide film having a thickness of 700 angstroms was formed by a CVD method using TEOS (tetraethoxysilane), and an opening was formed by patterning the silicon oxide film. Here, the width of the opening was 30 μm and the length was 3 cm. Amorphous silicon is exposed at the bottom of the opening.

  (C) A nickel acetate aqueous solution having a nickel concentration of 100 ppm (weight conversion) was applied by a spin coater as shown in FIG. (D) With the nickel acetate aqueous solution attached, a heat treatment was performed in a nitrogen atmosphere at a temperature of 600 ° C. (corresponding to the first heat treatment temperature) for 8 hours. (E) The mask of the silicon oxide film was removed to obtain a crystalline silicon film having a laterally grown region.

  (F) Heat treatment was performed for 20 minutes at a temperature of 950 ° C. (corresponding to the second heat treatment temperature) in an oxygen atmosphere (normal pressure) containing 3% by volume of HCl. As a result, an oxide film of 200 angstroms was formed, and the film thickness of the silicon film was 400 angstroms. As the film thickness of the crystalline silicon film decreases during the formation of the thermal oxide film, silicon that has not been crystallized or is not completely crystallized is consumed for the formation of the thermal oxide film, thereby improving the crystallinity. It is presumed that the inactivation of grain boundaries proceeds. Next, the oxide film formed in (G) and (F) was removed using buffered hydrofluoric acid.

  As is apparent from FIGS. 3 to 4, it can be seen that the crystal in the crystalline silicon film according to the present invention has the following characteristics (S) to (S). (C) The structure of the crystal lattice is continuously continuous in a specific direction. (F) Grows into thin rod-like crystals or thin flat rod-like crystals. (S) Grows into a plurality of thin rod-like crystals or thin flat rod-like crystals, and they grow in parallel or almost in parallel with a gap. Further, when viewing the photograph in FIG. 4, for example, a thin rod-like crystal having a width of about 0.15 μm extends in a diagonal direction from the lower left to the upper right, and there is a clear boundary (crystal grain boundary) at both width edges. I understand that. In addition, it is due to the difference in the orientation of the crystal plane between the rod-like crystals that the lines in the photographs of FIGS.

  In this regard, the crystalline silicon films obtained in each of the examples described later were also individually observed with an optical microscope and a transmission electron microscope, but there were differences in the crystal diameter (width). The diameter (width) of each crystal rod had a certain difference such as about 0.1 to 1 μm].

  As described above, the crystal in the crystalline silicon film according to the present invention grows in parallel or substantially in parallel regardless of whether it is viewed macroscopically or microscopically. have. From a different perspective, each of these crystals is a single crystal, but when viewed as an aggregate thereof, it can be said that it is a kind of poly-crystal state.

  FIGS. 7A to 7B show crystal growth assumed based on the results observed from a number of micrographs represented by FIGS. 1 to 4 for the crystalline silicon film obtained in the present invention. Is schematically illustrated. First, FIG. 7A shows a case where a metal element that promotes crystallization of silicon is present at one end of the amorphous silicon film surface and grown. In this case, the crystal of silicon grows linearly and in parallel or substantially in parallel with the crystal lattice continuously from the metal addition region.

  Next, FIG. 7B shows a case where a metal element that promotes crystallization of silicon is grown on the entire surface of the amorphous silicon film. In this case, the silicon crystal grows radially from the center of an infinite number of points on the entire surface of the amorphous silicon film, and each of the radial crystals grows in a rod shape with continuous crystal lattices. Moreover, when the positional relationship between adjacent radial crystal rods extending from the center of each point is seen, the crystal rods grow in parallel or almost in parallel to each other (when viewed as a whole, they are radial, that is, spread toward the end, but the crystal growth direction The crystal rods are parallel or nearly parallel to each other).

  By the way, it is effective to shorten the channel length in order to increase the operation speed of, for example, a TFT (the same applies to a general MOS transistor, but here the TFT is taken as an example, and this will be described mainly). . However, if the channel length is shortened to 1 μm or less, a disadvantage called a short channel effect occurs. Specifically, problems such as deterioration of subthreshold characteristics and a decrease in threshold value occur.

  Here, the subthreshold characteristic (also referred to as S value) means the rising characteristic at the time when the TFT switch is turned on, as schematically shown in FIG. Specifically, if the rising edge is steep, the subthreshold characteristic is good, and the TFT can operate at high speed. On the other hand, a TFT with poor subthreshold characteristics has a small rising curve slope (= curved curve) and is not suitable for high-speed operation.

  The deterioration of the subthreshold characteristic due to the short channel effect can be explained as follows based on the current technical knowledge (current technical knowledge or conventional theory). First, a shorter channel means a shorter distance between the source region and the drain region. In general, the channel is intrinsic (I-type semiconductor), and the source region and the drain region are N-type or P-type. For example, if an intrinsic semiconductor and an N-type semiconductor are in contact with each other, the properties of the N-type semiconductor as a semiconductor affect the inside of the intrinsic semiconductor. This can also be understood from an example of a PN junction model.

  In the case of TFT, the above effect will be exerted inside the channel. That is, an N-type or P-type influence is exerted from the source region and drain region to the inside of the channel. The extent of this effect, i.e., the distance over which it affects, does not change as the channel becomes shorter.

  As the channel length becomes shorter and shorter, the influence on the channel length from the source region and drain region to the channel cannot be ignored. In an extreme case, the distance of the influence exerted from the source region and the drain region to the inside of the channel may be longer than the channel length. In such a state, the change in the conductivity type of the channel is controlled by the application of the electric field from the gate electrode, and the operation of the TFT (the same applies to the MOS type transistor) in which the conductivity between the source region and the drain changes is an obstacle. Comes out. As a result, a state in which the subthreshold characteristic is deteriorated occurs.

  Accordingly, based on the above technical recognition (current technical knowledge or conventional theory), it is naturally expected that the short channel effect appears in the TFT using the crystalline silicon film obtained by the present invention. The However, in the TFT using the crystalline silicon film obtained by the present invention, it has been found that even if the channel length is 1 μm or less, the short channel effect does not appear and there is no such obstacle or deterioration.

  Crystals of the crystalline silicon film obtained in the present invention having the above-mentioned features (sa) to (su), that is, (sa) crystal lattice structures are continuously connected in a substantially specific direction. In a crystal that grows into a crystal or thin flat rod-like crystal, or (su) grows into a plurality of thin rod-like crystals or thin flat rod-like crystals, and they grow in parallel or nearly parallel at intervals In addition to the fact that the short channel effect is not observed, it has been shown that it exhibits a very good subthreshold characteristic that cannot be explained by conventional technical recognition, and operates at a high speed corresponding to this.

  Tables 1 and 2 and FIG. 9 show an example. The semiconductor device used here is generally manufactured by the following processes (H) to (L) following the process shown in FIG. These steps are illustrated as FIG. Note that step (G) in FIG. 6 corresponds to step (G) in the step shown in FIG.

The crystalline silicon film formed in the steps (H) and (A) to (F) was patterned to form an active layer of the thin film transistor. (I) Next, a silicon oxide film was formed as a GI film (gate insulator film) by a plasma CVD method using a mixed gas of SiH ₄ + N ₂ O as a film forming gas.

  (J) Heat treatment was performed at 950 ° C. for 28 minutes in an oxygen atmosphere (normal pressure) containing 3% by volume of HCl. As a result, a 300 angstrom thermal oxide film was formed, and the thickness of the crystalline silicon film was 250 angstrom. As the film thickness of the crystalline silicon film decreases during the formation of the thermal oxide film, silicon that has not been crystallized or is not completely crystallized is consumed for the formation of the thermal oxide film, thereby improving the crystallinity. It is presumed that the inactivation of grain boundaries proceeds. Further, the thermal oxide film formed here is formed on the surface of the active layer because activated oxygen molecules enter the GI film.

  (K) An aluminum film having a thickness of 4000 angstroms was formed by sputtering, and 0.18% by weight of scandium was contained in the aluminum. Further, an anodic oxide film of about 100 Å was formed on the surface of the aluminum film. (L) Next, a resist mask was placed and the aluminum film was patterned to produce a prototype gate electrode.

  Table 1 shows measured values for an N-channel TFT, and Table 2 shows a configuration for a P-channel TFT. In Tables 1 and 2, the measurement points 1 to 20 mean that the measurement points 1 to 20 were prepared using each part of the film surface of one batch of crystalline silicon film prepared as described above. First, as is apparent from Table 1, when an N-channel TFT is configured, the S value (S-value) is particularly small, and the value is very small, approximately 80 mV / decade, and 70 to 90 mV / total as a whole. It falls within the range of decade, and particularly in the case of the measurement point 13, a small value of 72.53 mV / decade is shown.

S value (sub-threshold coefficient) is defined as the inverse of the maximum gradient in the I _D over V _G rising part of the curve as shown in FIG. 8, in other words, required gate voltage to increase the drain current by one digit It is grasped as an increase of. That is, as the S value is smaller, the slope of the rising portion becomes steeper, the response as a switching element is excellent, and high-speed operation can be performed.

  The ideal value of the S value derived from the theoretical formula is 60 mV / decade. A transistor using a single crystal wafer has been obtained so far, but a TFT using a conventional general low-temperature polysilicon is used. Then, the limit is about 300 to 500 mV / dcade. From this, the S value of around 80 mV / decade in the TFT using the crystalline silicon film according to the present invention is an extremely excellent characteristic and can be said to be an amazing characteristic.

  Table 2 shows actual measurement values when the crystalline silicon film according to the present invention is used to form a P-channel TFT. As for the S value (S-value) in this case, as in the case of the N-channel TFT, in this case, the S value is very small, approximately 80 mV / decade, and 70 to 100 mV / dcade as a whole. In particular, the measurement point 4 shows a small value of 72.41 mV / decade. The meaning of these values is the same as in the case of the N-channel TFT only by looking at the plus (+) and minus (−) in reverse.

  In addition to the above, the meaning of each characteristic (symbol) in Tables 1 and 2 is as follows. As is clear from Tables 1 and 2, these characteristics are values that can be sufficiently practically used. Ion is a drain current that flows when the TFT is in the ON state. When VD = 1V (1 volt), Ion-1 (note that the horizontal bar “-” in Ion-1 is normally Although it is described below the center of the character as shown, it is drawn at the center of the character.This is the same for the following symbols having a horizontal bar “-”), and when VD = 5 V, Ion-2 It is said. A TFT having a larger Ion can pass a larger amount of current in a shorter time.

  Ioff is a drain current that flows when the TFT is in an OFF state. Ioff-1 is set when VD = 1V (1 volt), and Ioff-2 is set when VD = 5V. When current flows in the OFF state, power is consumed correspondingly. Therefore, it is extremely important to reduce Ioff. When Ioff is large, there is a problem that, for example, charge held in the liquid crystal flows out due to Ioff. .

  For Ion / Ioff-1 and Ion / Ioff-2, for example, Ion / Ioff-1 is the ratio of Ion-1 and Ioff-1 and how many digits the ON current and OFF current are. Only the difference. The larger the ratio of Ion / Ioff, the better the switching characteristics, and it is also important for increasing the contrast of the panel.

  Vth is a parameter generally called a threshold voltage, and is defined as a voltage at which a TFT is switched to an ON state, for example. The values in the table are values obtained by the route ID extrapolation method with VD = 5 as an evaluation target. If Vth is large, the voltage applied to the gate electrode must be set high, leading to an increase in drive voltage and further power consumption.

  μFE is field effect mobility and is also called mobility. μFE is a parameter indicating the ease of carrier movement, and a TFT having a large μFE is suitable for high-speed operation. As is clear from Tables 1 and 2, these characteristics are values that can be sufficiently practically used.

Figure 9 (a) ~ (b) may choose one from the above measured data representative values is a diagram showing a graph of actually measured the I _D over V _G characteristics. Of these, FIG. 9A shows the case of an N-channel type TFT, and FIG. 9B shows the case of a P-channel type TFT. In both cases, VD = 1V (1 volt) is shown. 9A to 9B, the horizontal axis indicates the gate voltage (V), the vertical axis indicates the drain current (A), and the vertical axis indicates the range of “1E-13” to “1E-01”, that is, It is in the range of 1 × 10 ⁻¹³ to 1 × 10 ⁻¹ A (ampere).

First, when we have the case of the N-channel type TFT Nitsu in FIG. 9 (a), the slope of the rising portion of the I _D over V _G curve, i.e. it can be seen that the curve in the linear region is out extremely steep. This indicates that the characteristic corresponding to the small S value appears as it is, and the time to be completely turned on is very short, the response as a switching element is excellent, and it can be operated at high speed. ing. In FIG. 9A, the gate voltage range of −6 to −0.5 V corresponds to Ioff in Table 1, but the drain current that flows when in the OFF state is extremely small, which is also excellent in this respect. It turns out that it has the property.

  Next, regarding FIG. 9B, even in the case of the P-channel TFT, the curve in the linear region is extremely steep, and the drain current that flows when it is in the OFF state is extremely small. As well as excellent properties. In addition, as for these technical meanings, the signs of plus (+) and minus (-) are only reversed compared to the case of an N-channel TFT.

  Tables 3 to 4 and FIG. 10 show that the second heat treatment temperature is set to a lower temperature (700 ° C.) than that described above in the crystallization after the application of the nickel acetate solution to the amorphous silicon film. ), And a crystalline silicon film produced by irradiating with laser light. The crystalline silicon film here is manufactured according to the manufacturing process in Example 28, which will be described later, as described in (1) to (3) below, and the semiconductor device used here is the above (H) to (L ).

  (1) A quartz substrate is used as a substrate, and a plasma CVD method is used to produce an amorphous silicon film on the surface. (2) A 100 ppm concentration nickel acetate aqueous solution is applied to the entire surface of the amorphous silicon film. (The crystal growth direction is perpendicular to the film surface, that is, the vertical growth), (3) This is heated in a nitrogen atmosphere at a temperature of 600 ° C. for 4 hours, and the second heating temperature is set. Except for the point set to 700 degreeC, it irradiated with laser light (a substrate is not heated at the time of this irradiation), and it produced similarly to the case of Example 28 about other processes.

As is apparent from Tables 3 and 4, there are some differences compared to the data in Tables 1 and 2, but in this case as well, excellent characteristics including S values are shown, and FIG. a) as is clear from ~ (b), the slope of the rising portion of the I _D over V _G curve, i.e. the curve in the linear region is compared in FIG. 9 (a) ~ (b) , although the sleeping some extent, Nevertheless, it can be seen that it appears quite steep.

  Next, FIG. 11A is a graph summarizing the curves shown in FIG. 9A and FIG. 10A for the N-channel TFT. Here, the curve indicated by the symbol K in FIG. 11A corresponds to the curve of FIG. 9A, and the curve indicated by the symbol T corresponds to the curve of FIG. As is clear from FIG. 11 (a), the slope of the linear region is steep in all cases, but the K curve is steeper than the T curve, and this is because the S value in the linear region is smaller. It corresponds.

  Further, in the case of the K curve, the ON current in the saturation region [the region on the right side from the gate voltage value of 0.5 V (V = 0.5) on the horizontal axis: Ion] in FIG. Bigger than the curve. Further, the current in the OFF region [region in the left side from the gate voltage value of −0.3 V in the horizontal axis: Ioff in FIG. 11A] is smaller in the case of the K curve than in the T curve.

  FIG. 11B shows typical characteristics of a TFT using an amorphous silicon film, which is probably the ideal characteristic of a TFT using an amorphous silicon film at the present time. It is understood as a characteristic. When this is compared with FIG. 11 (a), with respect to the curve of FIG. 11 (b), in the case of curve K, there is a marked difference between the curve (S value) in the linear region and the current value in the OFF region. In the case of the curve T, the current value in the OFF region is almost equal to or slightly lower than the curve in FIG. 11B, but the curve (S value) in the linear region is steeper. It shows more excellent characteristics.

  Tables 1 and 2 and FIG. 9 show crystalline silicon produced by setting the second heating temperature (950 ° C.) higher than the second heating temperature (700 ° C.) in the case of Tables 3 to 4 and FIG. This is the case with a membrane. And the case of Table 1-Table 2 and FIG. 9 has shown that the characteristic more excellent including the S value is obtained rather than the case of Table 3-Table 4 and FIG. However, as described above, in the case of Tables 3 to 4 and FIG. 10 as well, it is considerably superior to the TFT that seems to use the most excellent amorphous silicon film among the conventional amorphous silicon films. It is clear that it exhibits effective characteristics.

  Further, FIGS. 13A to 13B show that a nine-stage ring oscillator is manufactured by assembling a circuit combining the N-channel TFT and the P-channel TFT having the characteristics shown in FIG. This is an oscilloscope (oscillation waveform). This circuit works so that the N-channel TFT and the P-channel TFT simultaneously complement each other's operation, and when one TFT discharges electric charge, the other TFT operates to absorb electric charge.

  FIG. 12 is a schematic diagram for explanation of FIG. 13. When FIG. 12 is viewed as a whole, the + side waveform of the oscillation waveform mainly relates to N-channel operation, and the − side waveform is the main waveform. Are related to P-channel operation. Therefore, for example, when oscillating at a frequency of 152.0 MHz or 252.9 MHz, if the oscillation waveform maintains symmetry on the + side and the − side, the N-channel type is used at that frequency. The TFT and the P-channel TFT operate symmetrically and operate normally with similar characteristics.

  Accordingly, when the oscilloscopes shown in FIGS. 13A to 13B are viewed, the oscillation waveform is a positive sine wave, and no distortion is linearly observed. Thus, the crystalline silicon film according to the present invention exhibits excellent characteristics both when applied as an N-channel type and when applied as a P-channel type, and substantially between them. It can be seen that there is no difference in characteristics.

  A model that can explain the above phenomena and characteristics is considered as follows. First, as shown in the electron micrographs represented by FIGS. 3 to 4, the silicon semiconductor thin film constituting the TFT composed of the crystalline silicon film obtained in the present invention has a specific direction as described above. It has a structure with crystal continuity, and detailed observation by an electron microscope on many samples confirmed that the structure of the crystal lattice is continuous in a specific direction.

  Similarly, according to the observation result, the state is interpreted as a state in which the single crystal state continues in a specific direction at a predetermined interval. Naturally, it is understood that carriers easily move in a direction in which the lattice structure is continuous. That is, it is considered that in the TFT using the crystalline silicon film obtained by the present invention, a channel region is constituted by an infinite number of elongated channels.

  Here, it is a grain boundary that looks like a line, which is observed by transmission electron micrographs represented by FIGS. 3 to 4. No particular segregation of impurities has been observed at the grain boundaries.

  This crystal grain boundary is an inactive grain boundary having a low electrical activity, and has a structure in which no deep gap level exists or almost does not exist. However, it is considered that the energy is higher than other regions due to non-uniformity and discontinuity. Therefore, it is presumed that the carrier has a function of regulating the movement of the carrier in the direction in which the crystal structure is continuous. In addition, when such a narrow minute channel is formed, the permeation distance of the influence from the source region and the drain region exerted on the inside of the minute channel is considered to be reduced correspondingly. It is done.

  The electrical effects as described above can be inferred from ideally spreading two-dimensionally or three-dimensionally isotropically, for example, as inferred from the manner in which electromagnetic waves spread in a place free of obstacles. The In view of this, in the TFT using the crystalline silicon film obtained in the present invention, a state in which a large number of minute narrow channels are formed is realized. Therefore, in each channel, from the source region and the drain region, It can be understood that the influence on the channel is suppressed and that the short channel effect is suppressed as a whole.

  14 and 15 show a crystalline silicon film formed by utilizing a metal element that promotes crystallization of silicon in the process of many studies and tests conducted up to the present invention. This is a measured value of the gate current value of a planar type thin film transistor that was prototyped by the present inventors using a crystalline silicon film having a reduced concentration of the metal element. The difference between FIG. 14 and FIG. 15 depends on whether a thermal oxidation method or a plasma CVD method is used as a method for forming the gate insulating film.

  That is, FIG. 14 shows measured values when the gate insulating film is formed by the thermal oxide film, and FIG. 15 shows measured values when the gate insulating film is formed by the plasma CVD method. 14 and 15, the horizontal axis represents the gate current, and the vertical axis represents the number of measurement samples. A quartz substrate was used as the substrate here. The active layer was formed by a method in which nickel element was brought into contact with the surface of the amorphous silicon film and crystallized by a heat treatment at a temperature of 640 ° C. for 4 hours. Further, the thermal oxide film was formed in an oxygen atmosphere at a temperature of 950 ° C.

  From FIG. 14, it can be seen that the gate current value varies greatly depending on the sample. This indicates that the film quality of the gate insulating film varies. On the other hand, in the thin film transistor in which the gate insulating film shown in FIG. 15 is formed by the plasma CVD method, the variation in the gate current is small and the value is extremely small. The difference between the measurement values shown in FIGS. 14 and 15 is explained as the following reason.

  That is, in the sample in which the gate insulating film is formed with the thermal oxide film, the nickel element is sucked from the active layer into the thermal oxide film when the thermal oxide film is formed. As a result, nickel elements that impede the insulation are present in the thermal oxide film. Due to the presence of this nickel element, the current value leaking through the gate insulating film increases and the value varies.

This was also supported by measuring the concentration of nickel element in the gate insulating film of the sample from which the measured values in FIGS. 14 and 15 were obtained by SIMS (secondary ion analysis method). That is, 10 ¹⁷ cm ⁻³ or more of nickel element is measured in the gate insulating film formed by the thermal oxidation method, but the concentration of nickel element is measured in the gate insulating film formed by the plasma CVD method. Was confirmed to be 10 ¹⁶ cm ⁻³ or less. In addition, the impurity concentration described in this specification is defined as the minimum value of the measured value measured by SIMS (secondary ion analysis method).

  The above are several examples of the findings obtained by the present inventors in the course of numerous experiments and examinations carried out until the present invention and confirming the characteristics, effects, etc. The present invention is also based on such knowledge. And the above fact is common to the various aspects in this invention.

  Regardless of whether it is an amorphous silicon film or a crystalline silicon film, in a semiconductor device comprising a thin film transistor (TFT or the like) using a silicon film, the metal element is usually a harmful substance. The metal element needs to be removed from the silicon film as much as possible. According to the present invention, these metal elements that promote the crystallization of silicon can be removed or reduced very effectively after being used for forming a crystalline silicon film.

  In the present invention, a thermal oxide film is formed on the surface of a crystalline silicon film obtained by using a metal element that promotes crystallization of silicon, so that the metal element is gettered in the thermal oxide film. As a result, the concentration of the metal element in the crystalline silicon film is reduced or the metal element is removed. Thus, according to the present invention, a semiconductor device having excellent characteristics can be obtained.

  The main aspects of the inventions (1) to (6) are as follows. In the inventions (1) to (2), an amorphous silicon film is first formed. Next, this amorphous silicon film is crystallized by the action of a metal element that promotes crystallization of silicon typified by nickel to obtain a crystalline silicon film. This crystallization is performed by heat treatment. In this state after the heat treatment, the crystalline silicon film contains the metal element intentionally introduced at a certain high concentration.

  The crystalline silicon film in the above state is subjected to a heat treatment in an oxidizing atmosphere to form a thermal oxide film on the surface of the crystalline silicon film. At this time, the metal element is gettered in the thermal oxide film by the action of oxygen in the oxidizing atmosphere, and the concentration of the metal element in the crystalline silicon film is reduced or the metal element is removed. . Next, the thermal oxide film gettered with the metal element is removed.

  By these treatments, a crystalline silicon film having high crystallinity and from which the metal element is removed or a crystalline silicon film having a low concentration of the metal element can be obtained. The thermal oxide film can be removed using, for example, buffer hydrofluoric acid or other hydrofluoric acid-based etchants. The removal process of the thermal oxide film is the same as the removal process of the thermal oxide film in each invention described below.

  In the invention of (3), following the above steps, patterning is performed to form an active layer of the thin film transistor. The active layer is composed of a crystalline silicon film from which the metal element is removed or a crystalline silicon film having a low concentration of the metal element. Next, a semiconductor device is formed by forming a thermal oxide film constituting at least a part of the gate insulating film on the surface of the active layer by thermal oxidation.

  In the invention of (4), after an amorphous silicon film is first formed, a metal element that promotes crystallization of silicon is selectively introduced into the amorphous silicon film. As a mode for selectively introducing the metal element, (a) it is introduced into one end of the amorphous silicon film as long as silicon can be crystallized parallel to the film surface in the amorphous silicon film. (B) Introducing at one end of the amorphous silicon film at intervals, (c) Introducing into the whole surface of the amorphous silicon film at intervals, there is no particular limitation, but preferably Introducing from (a) of the above-mentioned aspects (a) to (e), that is, from a slit-like surface at an appropriate place on the film surface of the amorphous silicon film. Thereafter, crystal growth is performed in a direction parallel to the film from a region where the metal element is selectively introduced by a first heat treatment.

  Next, a second heat treatment is performed in an oxidizing atmosphere to form a thermal oxide film on the surface of the region where the crystal growth has been performed. At this time, the metal element is gettered in the thermal oxide film by the action of oxygen in the oxidizing atmosphere, and the concentration of the metal element in the crystalline silicon film is reduced or the metal element is removed. . Further, the thermal oxide film is removed, and an active layer of the semiconductor device is formed using the region from which the thermal oxide film has been removed.

In any of these forms, the second heat treatment temperature is preferably higher than the first heat treatment temperature, and depends on the plasma atmosphere containing oxygen and hydrogen after the removal of the thermal oxide film. It is preferable to perform annealing. Further, the oxygen concentration contained in the amorphous silicon film is preferably in the range of 5 × 10 ¹⁷ cm ⁻³ to 2 × 10 ¹⁹ cm ⁻³ .

  In the invention of (5), first, a silicon oxide film or a silicon oxynitride film is formed on a glass substrate or a quartz substrate. Next, in the same manner as described above, a crystalline silicon film is sandwiched between the first and second oxide films, and the crystalline silicon film contains a metal element that promotes crystallization of silicon, In the crystalline silicon film, a semiconductor device having a high concentration distribution of the metal element in the vicinity of the interface with the first and / or second oxide film is obtained. As an aspect of this semiconductor device, the first oxide film is a silicon oxide film or a silicon oxynitride film formed on a glass substrate or a quartz substrate, the crystalline silicon film constitutes an active layer of the thin film transistor, and the second The oxide film can be formed as a silicon oxide film or a silicon oxynitride film constituting the gate insulating film.

  In the invention of (6), in the same manner as described above, a base film made of an oxide film, a crystalline silicon film formed on the base film, and a thermal oxide film formed on the crystalline silicon film The crystalline silicon film contains a metal element that promotes crystallization of silicon, and the metal element that promotes crystallization of silicon is high in the vicinity of the interface with the base and / or the thermal oxide film. A semiconductor device having a concentration distribution and in which the thermal oxide film forms at least a part of the gate insulating film of the thin film transistor can be obtained.

  The main aspects of the inventions (7) to (12) are as follows. In the invention of (7), an amorphous silicon film is first formed. A metal element that promotes crystallization of silicon is intentionally introduced into this, and the amorphous silicon film is crystallized by a first heat treatment to obtain a crystalline silicon film. This crystallization is performed by heat treatment. In the state after this heat treatment, the metal element is contained in the crystalline silicon film. Next, a second heat treatment is performed in an oxidizing atmosphere containing a halogen element to form a thermal oxide film.

  At this time, the metal element is transferred or gettered into the thermal oxide film by the action of oxygen, the action of halogen, and the action of halogen and oxygen. At the same time, the nickel element is caused by the action of halogen such as chlorine. Is vaporized and removed to the outside. The concentration of the metal element in the crystalline silicon film is reduced or the metal element is removed. Next, after removing the thermal oxide film formed there, a thermal oxide film is formed on the surface of the region from which the thermal oxide film has been removed by thermal oxidation again.

  In the invention of (8), an amorphous silicon film is first formed. A metal element that promotes crystallization of silicon is intentionally introduced into the amorphous silicon film, and then the amorphous silicon film is crystallized by a first heat treatment to obtain a crystalline silicon film. Next, a second heat oxidation treatment is performed in an oxidizing atmosphere containing a halogen element, a thermal oxide film is formed on the surface of the crystalline silicon film, and the metal element is transferred or gettered to the thermal oxide film. At the same time, the nickel element is vaporized and removed to the outside by the action of a halogen such as chlorine. This removes or reduces the metal element present in the crystalline silicon film. Then, after removing the thermal oxide film formed there, a thermal oxide film is formed on the surface of the region from which the thermal oxide film has been removed by thermal oxidation again.

  In the invention of (9), an amorphous silicon film is first formed. A metal element for promoting crystallization of silicon is intentionally introduced into the amorphous silicon film, and then the amorphous silicon film is crystallized by a first heat treatment to obtain a crystalline silicon film. Next, a second heat oxidation treatment is performed in an oxidizing atmosphere containing a halogen element, and the metal element is transferred or gettered to the thermal oxide film formed at this time. The nickel element is vaporized and removed by the action.

  This removes or reduces the metal element present in the crystalline silicon film. After removing the thermal oxide film formed here, patterning is performed to form an active layer of the thin film transistor, and a thermal oxide film constituting at least part of the gate insulating film is formed on the surface of the active layer by thermal oxidation To do.

  In the invention of (10), first, an amorphous silicon film is formed. A metal element for promoting crystallization of silicon is selectively introduced into the amorphous silicon film. As a mode for selectively introducing the metal element, (a) it is introduced into one end of the amorphous silicon film as long as silicon can be crystallized parallel to the film surface in the amorphous silicon film. (B) Introducing at one end of the amorphous silicon film at intervals, (c) Introducing into the whole surface of the amorphous silicon film at intervals, there is no particular limitation, but preferably Introducing from (a) to (e) of the embodiments (a) to (i), that is, from slit-like surfaces at appropriate locations on the surface of the amorphous silicon film. Thereafter, crystal growth is performed in a direction parallel to the film from a region where the metal element is selectively introduced by a first heat treatment.

  Next, a second heat treatment is performed in an oxidizing atmosphere containing a halogen element to form a thermal oxide film on the surface of the region where the crystal growth has been performed, and the metal element is transferred or gettered to the thermal oxide film. At the same time, nickel element is vaporized and removed by the action of halogen such as chlorine. This removes or reduces the metal element present in the crystalline silicon film. Next, after removing the thermal oxide film, an active layer of the semiconductor device is formed using the region from which the thermal oxide film has been removed. The active layer is composed of a crystalline silicon film from which the metal element is removed or a crystalline silicon film having a low concentration of the metal element.

The oxidizing atmosphere containing the halogen element in the semiconductor device manufacturing methods (7) to (10) above is selected from HCl, HF, HBr, Cl ₂ , F ₂ and Br _{2 in} the O ₂ atmosphere. An atmosphere to which one or more kinds of gases are added can be used. As each heating temperature, the second heat treatment temperature is preferably higher than the first heat treatment temperature, and annealing in a plasma atmosphere containing oxygen and hydrogen is performed after removal of the thermal oxide film. preferable. Furthermore, the oxygen concentration contained in the amorphous silicon film is preferably in the range of 5 × 10 ¹⁷ cm ⁻³ to 2 × 10 ¹⁹ cm ⁻³ .

  In the invention of (11), first, a silicon oxide film or a silicon oxynitride film is formed on a glass substrate or a quartz substrate. Next, in the same manner as described above, a crystalline silicon film is sandwiched between the first and second oxide films, and the crystalline silicon film contains a metal element that promotes crystallization of silicon, In the crystalline silicon film, a semiconductor device having a high concentration distribution of the metal element in the vicinity of the interface with the first and / or second oxide film is obtained.

  In this semiconductor device, a halogen element is contained in a high concentration distribution in the first oxide film and / or in the vicinity of the interface between the first oxide film and the crystalline silicon film, and in the crystalline silicon film. In the vicinity of the interface with the second oxide film, a halogen element is contained with a high concentration distribution. In this case, the first oxide film is a silicon oxide film or a silicon oxynitride film formed on a glass substrate or a quartz substrate, and the crystalline silicon film constitutes an active layer of the thin film transistor, and the second The oxide film is composed of a silicon oxide film or a silicon oxynitride film constituting a gate insulating film.

  In the invention of (12), a base film made of an oxide film, a crystalline silicon film formed on the base film, and a thermal oxide film formed on the crystalline silicon film are formed in the same manner as described above. The crystalline silicon film contains a metal element that promotes crystallization of silicon and hydrogen and a halogen element, and the metal element that promotes crystallization of silicon is an interface with the base and / or the thermal oxide film. The halogen element has a high concentration distribution in the vicinity, and the halogen element has a high concentration distribution in the vicinity of the interface with the base and / or the thermal oxide film, and the thermal oxide film forms at least a part of the gate insulating film of the thin film transistor. A semiconductor device is configured.

  The main aspects of the inventions (13) to (17) are as follows. In the invention of (13), first, an amorphous silicon film is formed. A metal element that promotes crystallization of silicon is intentionally introduced into this, and the amorphous silicon film is crystallized by a first heat treatment to obtain a crystalline silicon film. Thereafter, the crystalline silicon film is irradiated with laser light or strong light. Next, a second heat treatment is performed in an oxidizing atmosphere containing a halogen element to remove or reduce the metal element present in the crystalline silicon film. Further, the thermal oxide film formed here is removed, and a thermal oxide film is formed on the surface of the region from which the thermal oxide film has been removed by thermal oxidation again.

  In the invention of (14), an amorphous silicon film is first formed. A metal element for promoting crystallization of silicon is intentionally introduced into the amorphous silicon film, and the amorphous silicon film is crystallized by a first heat treatment to obtain a crystalline silicon film. The crystalline silicon film is irradiated with laser light or strong light to diffuse the metal element present in the crystalline silicon film in the crystalline silicon film.

  Next, second heat treatment is performed in an oxidizing atmosphere containing a halogen element, so that the metal element present in the crystalline silicon film is transferred or gettered into the thermal oxide film. The thermal oxide film formed here is removed, and a thermal oxide film is formed on the surface of the region from which the thermal oxide film has been removed by thermal oxidation again.

  In the invention of (15), an amorphous silicon film is first formed. A metal element that promotes crystallization of silicon is intentionally and selectively introduced into the amorphous silicon film. As a mode for selectively introducing the metal element, (a) it is introduced into one end of the amorphous silicon film as long as silicon can be crystallized parallel to the film surface in the amorphous silicon film. (B) Introducing at one end of the amorphous silicon film at intervals, (c) Introducing into the whole surface of the amorphous silicon film at intervals, there is no particular limitation, but preferably Introducing from (a) of the above-mentioned aspects (a) to (e), that is, from a slit-like surface at an appropriate place on the film surface of the amorphous silicon film.

  Thereafter, the amorphous silicon film is subjected to a first heat treatment, and crystal growth is performed in a direction parallel to the film from a region where the metal element is selectively introduced. Next, laser light or intense light is irradiated to diffuse the metal element present in the crystal grown region. Further, the second heat treatment is performed in an oxidizing atmosphere containing a halogen element, and the metal element present in the crystal-grown region is transferred to the thermal oxide film formed by the second heat treatment. Gettering. Next, after removing the thermal oxide film formed here, a thermal oxide film is formed on the surface of the region from which the thermal oxide film has been removed by thermal oxidation again.

In the inventions of the above (13) to (15), it is preferable that the second processing temperature is higher than 600 ° C. and 750 ° C. or lower, and the gate insulating film is formed using the thermal oxide film again. Preferably formed. In these inventions, the oxidizing atmosphere containing the halogen element is one or plural kinds of gases selected from HCl, HF, HBr, Cl ₂ , F ₂ , and Br ₂ in the O ₂ atmosphere. An atmosphere is used.

Furthermore, in these inventions (13) to (15), it is preferable that the second heat treatment temperature is higher than the first heat treatment temperature, and oxygen and hydrogen are removed after the thermal oxide film is removed. Annealing can be performed in a plasma atmosphere. In these inventions, the oxygen concentration contained in the amorphous silicon film is preferably in the range of 5 × 10 ¹⁷ cm ⁻³ to 2 × 10 ¹⁹ cm ⁻³ .

  In the invention of (16), an amorphous silicon film is first formed. After intentionally introducing a metal element that promotes crystallization of silicon into this amorphous silicon film, the amorphous silicon film is crystallized by a first heat treatment to obtain a crystalline silicon film. Next, the crystalline silicon film is patterned to form an active layer of a semiconductor device, and the active layer is irradiated with laser light or strong light. Thereafter, a second heat treatment is performed in an oxidizing atmosphere containing a halogen element to remove or reduce the metal element present in the active layer. Subsequently, the thermal oxide film formed here is removed, and a thermal oxide film is formed on the surface of the active layer by thermal oxidation again.

  In the invention of (17), an amorphous silicon film is first formed. A metal element that promotes crystallization of silicon is intentionally introduced into the amorphous silicon film, and the amorphous silicon film is crystallized by a first heat treatment to obtain a crystalline silicon film. The crystalline silicon film is patterned to form an active layer of a semiconductor device, and the active layer is irradiated with laser light or strong light. Next, a second heat treatment is performed in an oxidizing atmosphere containing a halogen element to remove or reduce the metal element present in the active layer. Thereafter, the thermal oxide film formed here is removed, and a thermal oxide film is formed on the surface of the active layer by thermal oxidation again. At this time, the active layer is configured to have an inclined shape whose side surface forms an angle of 20 ° to 50 ° with the base surface.

In the inventions of the above (16) to (17), the gate insulating film can be constituted by using the thermal oxide film again. It is preferable that the first heat treatment temperature and the upper limit of the second heat treatment temperature is 750 ° C. or less, and as the oxidizing atmosphere containing a halogen element, HCl preferably in an O ₂ atmosphere, HF, An atmosphere to which one or plural kinds of gases selected from HBr, Cl ₂ , F ₂ and Br ₂ are added is used.

Furthermore, in these inventions, the second heat treatment temperature is preferably higher than the first heat treatment temperature, and annealing is performed in a plasma atmosphere containing oxygen and hydrogen after the removal of the thermal oxide film. be able to. The oxygen concentration contained in the amorphous silicon film is preferably in the range of 5 × 10 ¹⁷ cm ⁻³ to 2 × 10 ¹⁹ cm ⁻³ .

  The main aspects of the inventions (18) to (22) are as follows. In the invention of (18), an amorphous silicon film is first formed. A metal element for promoting crystallization of silicon is intentionally introduced into the amorphous silicon film, and the amorphous silicon film is crystallized by a first heat treatment to obtain a crystalline silicon film. Next, the crystalline silicon film is irradiated with laser light or strong light, and a second heat treatment is performed in an oxidizing atmosphere to remove or reduce the metal element present in the crystalline silicon film. . Thereafter, the thermal oxide film formed in the step is removed, and a thermal oxide film is formed on the surface of the region from which the thermal oxide film has been removed by thermal oxidation again.

  In the invention of (19), an amorphous silicon film is first formed. After intentionally introducing a metal element that promotes crystallization of silicon into this amorphous silicon film, the amorphous silicon film is crystallized by a first heat treatment to obtain a crystalline silicon film. Next, the metal element present in the crystalline silicon film is diffused in the crystalline silicon film by irradiating the crystalline silicon film with laser light or strong light. Thereafter, a second heat treatment is performed in an oxidizing atmosphere, and the metal element present in the crystalline silicon film is transferred or gettered into the thermal oxide film to be formed. Further, after the thermal oxide film formed here is removed, a thermal oxide film is formed on the surface of the region from which the thermal oxide film has been removed by thermal oxidation again.

  In the invention (20), first, an amorphous silicon film is formed. A metal element that promotes crystallization of silicon is intentionally and selectively introduced into the amorphous silicon film. As a mode for selectively introducing the metal element, (a) it is introduced into one end of the amorphous silicon film as long as silicon can be crystallized parallel to the film surface in the amorphous silicon film. (B) Introducing at one end of the amorphous silicon film at intervals, (c) Introducing into the whole surface of the amorphous silicon film at intervals, there is no particular limitation, but preferably Introducing from (a) of the above-mentioned aspects (a) to (e), that is, from a slit-like surface at an appropriate place on the film surface of the amorphous silicon film.

  Next, a first heat treatment is performed on the amorphous silicon film, and crystal growth is performed in a direction parallel to the film from the region where the metal element is intentionally and selectively introduced. Thereafter, laser light or intense light is irradiated to diffuse the metal element present in the crystal-grown region. Next, second heat treatment is performed in an oxidizing atmosphere, and the metal element present in the crystal-grown region is transferred or gettered into the thermal oxide film formed by the second heat treatment. Further, the thermal oxide film formed here is removed, and a thermal oxide film is formed on the surface of the region from which the thermal oxide film has been removed by thermal oxidation again.

In the above inventions (18) to (20), the second heat treatment temperature is preferably performed at a temperature exceeding 600 ° C. and 750 ° C. or less, and using the thermal oxide film again, the gate insulating film Can be formed. In these inventions, the second heat treatment temperature is preferably higher than the first heat treatment temperature. Furthermore, in these inventions, annealing in a plasma atmosphere containing oxygen and hydrogen can be performed after removing the thermal oxide film. The oxygen concentration contained in the amorphous silicon film is preferably in the range of 5 × 10 ¹⁷ cm ⁻³ to 2 × 10 ¹⁹ cm ⁻³ .

  In the invention (21), an amorphous silicon film is first formed. A metal element for promoting crystallization of silicon is intentionally introduced into the amorphous silicon film, and the amorphous silicon film is crystallized by a first heat treatment to obtain a crystalline silicon film. Next, the crystalline silicon film is patterned to form an active layer of a semiconductor device, and the active layer is irradiated with laser light or strong light. Thereafter, a second heat treatment is performed in an oxidizing atmosphere to remove or reduce the metal element present in the active layer. Next, the thermal oxide film formed here is removed, and a thermal oxide film is formed on the surface of the active layer by thermal oxidation again.

  In the invention of (22), an amorphous silicon film is first formed. After intentionally introducing a metal element that promotes crystallization of silicon into this amorphous silicon film, the amorphous silicon film is crystallized by a first heat treatment to obtain a crystalline silicon film. Next, the crystalline silicon film is patterned to form an active layer of a semiconductor device, and the active layer is irradiated with laser light or strong light. Thereafter, a second heat treatment is performed in an oxidizing atmosphere to remove or reduce the metal element present in the active layer. The thermal oxide film formed here is removed, and a thermal oxide film is formed on the surface of the active layer by thermal oxidation again. At this time, the active layer is configured to have an inclined shape in which an angle between the side surface and the base surface is preferably 20 ° to 50 °.

In the above inventions (21) to (22), the gate insulating film can be formed by using the thermal oxide film again. The second treatment temperature is preferably higher than 600 ° C. and 750 ° C. or less, and the second heat treatment temperature is preferably higher than the first heat treatment temperature. Further, in these inventions, it is preferable to perform annealing in a plasma atmosphere containing oxygen and hydrogen after removing the thermal oxide film, and the oxygen concentration contained in the amorphous silicon film is 5 × 10 ¹⁷ cm ^−. The range is preferably ^{3 to} 2 × 10 ¹⁹ cm ⁻³ .

  The main aspects of the inventions (23) to (25) are as follows. In the invention of (23), first, an amorphous silicon film is formed on a substrate having an insulating surface, and a metal element for promoting crystallization of silicon is intentionally introduced into the amorphous silicon film. Next, the amorphous silicon film is crystallized by a first heat treatment at a temperature of 750 ° C. to 1100 ° C. to obtain a crystalline silicon film, and then the crystalline silicon film is patterned to form an active layer of the semiconductor device. .

  Thereafter, a second heat treatment is performed in an oxidizing atmosphere containing a halogen element to remove or reduce the metal element present in the active layer. After removing the thermal oxide film formed here and removing the thermal oxide film, a thermal oxide film is formed by thermal oxidation again. At this time, it is preferable that the temperature of the second heat treatment be higher than that of the first heat treatment.

  In the invention of (24), after an amorphous silicon film is first formed on a substrate having an insulating surface, a metal element that promotes crystallization of silicon is intentionally introduced into the amorphous silicon film. Next, the amorphous silicon film is crystallized by a first heat treatment at a temperature of 750 ° C. to 1100 ° C. to obtain a crystalline silicon film. Thereafter, after patterning the crystalline silicon film to form an active layer of the semiconductor device, a second heat treatment is performed in an oxidizing atmosphere containing a halogen element, and the metal element present in the active layer is removed. Then, migration or gettering is performed in the thermal oxide film formed by the second heat treatment. Next, after removing the thermal oxide film formed in this step, a thermal oxide film is formed by thermal oxidation again. At this time, preferably, the temperature of the second heat treatment is set higher than the temperature of the first heat treatment.

  In the invention of (25), an amorphous silicon film is first formed on a substrate having an insulating surface, and a metal element that promotes crystallization of silicon is intentionally and selectively introduced into the amorphous silicon film. . As a mode for selectively introducing the metal element, (a) it is introduced into one end of the amorphous silicon film as long as silicon can be crystallized parallel to the film surface in the amorphous silicon film. (B) Introducing at one end of the amorphous silicon film at intervals, (c) Introducing into the whole surface of the amorphous silicon film at intervals, there is no particular limitation, but preferably Introducing from (a) of the above-mentioned aspects (a) to (e), that is, from a slit-like surface at an appropriate place on the film surface of the amorphous silicon film.

  Next, by a first heat treatment at a temperature of 750 ° C. to 1100 ° C., crystal growth is performed in a direction parallel to the film from a region where the metal element of the amorphous silicon film is intentionally and selectively introduced. Next, patterning is performed to form an active layer of the semiconductor device using a region where the crystal has grown in a direction parallel to the film. Thereafter, a second heat treatment is performed in an oxidizing atmosphere containing a halogen element, and the metal element present in the active layer is transferred or gettered into the thermal oxide film formed by the second heat treatment. Ring. Further, after removing the thermal oxide film, a thermal oxide film is formed by thermal oxidation again. At this time, preferably, the temperature of the second heat treatment is set higher than the temperature of the first heat treatment.

As described above, in the inventions of (23) to (25), a quartz substrate is preferably used as a substrate on which an amorphous silicon film is formed, and a gate insulating film is formed using a second thermal oxide film. Further, in the inventions of (23) to (25), annealing can be performed in a plasma atmosphere containing oxygen and hydrogen after the removal of the thermal oxide film, and the oxygen concentration contained in the amorphous silicon film is reduced. A range of 5 × 10 ¹⁷ cm ^{−3 to} 2 × 10 ¹⁹ cm ⁻³ is preferable.

  The main aspects of the inventions (26) to (29) are as follows. In the invention of (26), an amorphous silicon film is first formed. After the surface of the amorphous silicon film is held in contact with a metal element that promotes crystallization of silicon, a first heat treatment is performed to crystallize the amorphous silicon film to obtain a crystalline silicon film. Next, after performing a second heat treatment at a temperature of 500 ° C. to 700 ° C. in an atmosphere containing oxygen, hydrogen, and fluorine to form a thermal oxide film on the surface of the crystalline silicon film, the thermal oxide film Remove.

  In the invention of (27), an amorphous silicon film is first formed. After the surface of the amorphous silicon film is held in contact with a metal element that promotes crystallization of silicon, a first heat treatment is performed to crystallize the amorphous silicon film to obtain a crystalline silicon film. Next, after performing a second heat treatment at a temperature of 500 ° C. to 700 ° C. in an atmosphere containing oxygen, hydrogen, fluorine, and chlorine to form a thermal oxide film on the surface of the crystalline silicon film, the thermal oxidation is performed. Remove the membrane.

  In the invention of (28), an amorphous silicon film is first formed. A metal element that promotes crystallization of silicon is held in contact with the surface of the amorphous silicon film, and then heat treatment is performed to crystallize the amorphous silicon film to obtain a crystalline silicon film. Next, after forming a wet oxide film on the surface of the crystalline silicon film in an atmosphere containing fluorine and / or chlorine, the oxide film is removed.

  As described above, in the inventions (26) to (28), the concentration of the metal element in the oxide film is preferably higher than the concentration of the metal element in the crystalline silicon film. The atmosphere in which the second heat treatment is performed preferably contains hydrogen at a concentration of 1% by volume or more and the explosion limit or less. Further, the first heat treatment is preferably performed in a reducing atmosphere, and laser light can be irradiated to the crystalline silicon film after the first heat treatment.

The invention of (29) is a semiconductor device having a crystalline silicon film, wherein a metal element that promotes crystallization of silicon is 1 × 10 ¹⁶ cm ^{−3 to} 5 × 10 ¹⁸ cm ^{−. 3 with} a concentration of fluorine atoms of 1 × 10 ¹⁵ cm ⁻³ to 1 × 10 ²⁰ cm ⁻³ and hydrogen atoms of 1 × 10 ¹⁷ cm ⁻³ to 1 × 10 ²¹ cm ⁻³ . It is a semiconductor device characterized in that it is contained in a concentration. This semiconductor device can be manufactured by the manufacturing methods (26) to (28). In addition, the silicon film in the semiconductor device is preferably formed on an insulating film, and fluorine atoms are preferably present in a high concentration distribution in the vicinity of the interface between the insulating film and the silicon film.

  The main aspects of the inventions (30) to (33) are as follows. In the invention (30), an amorphous silicon film is first formed, and the amorphous silicon film is crystallized to form a crystalline silicon film. Next, the crystalline silicon film is heated in an oxidizing atmosphere to which a fluorine compound gas is added to grow a thermal oxide film on the surface of the crystalline silicon film, and then the thermal oxide film on the surface of the crystalline silicon film is formed. Remove. Then, a semiconductor device is manufactured by depositing an insulating film on the surface of the crystalline silicon film.

  In the invention of (31), an amorphous silicon film is formed and crystallized by irradiating it with a laser beam to form a crystalline silicon film. Next, the crystalline silicon film is heated in an oxidizing atmosphere to which a fluorine compound gas is added to grow a thermal oxide film on the surface of the crystalline silicon film, and then the thermal oxide film on the surface of the crystalline silicon film is formed. Remove. Then, a semiconductor device is manufactured by depositing an insulating film on the surface of the crystalline silicon film.

  The invention (32) is a method for manufacturing a thin film transistor over a substrate having an insulating surface. First, an amorphous silicon film is formed, and the amorphous silicon film is crystallized to form a crystalline silicon film. Thereafter, heating is performed in an oxidizing atmosphere to which a fluorine compound gas is added to grow a thermal oxide film on the surface of the crystalline silicon film, and then the thermal oxide film on the surface of the crystalline silicon film is removed.

  Next, after forming the active layer of the thin film transistor by shaping the crystalline silicon film, an insulating film is deposited on the surface of the active layer, and a gate insulating film is formed at least on the surface of the channel region. Further, a gate electrode is formed on the surface of the gate insulating film, impurity ions imparting a conductivity type are implanted into the active layer using the gate electrode as a mask, and a source and a drain are formed in a self-aligned manner. Make the device.

  The invention of (33) is a method for manufacturing a thin film transistor over a substrate having an insulating surface. First, an amorphous silicon film is formed, and the amorphous silicon film is crystallized to form a crystalline silicon film. Next, after irradiating the crystalline silicon film with laser light, heating in an oxidizing atmosphere to which a fluorine compound gas has been added to grow a thermal oxide film on the surface of the crystalline silicon film, the crystalline silicon film The thermal oxide film on the surface is removed.

  Next, the crystalline silicon film is shaped to form an active layer of the thin film transistor, an insulating film is deposited on the surface of the active layer to form a gate insulating film on at least the surface of the channel region, and the gate insulating film A gate electrode is formed on the surface of the substrate. Further, impurity ions imparting a conductivity type are implanted into the active layer using the gate electrode as a mask, and a source and a drain are formed in a self-aligned manner to manufacture a semiconductor device.

In the above inventions (30) to (33), the thickness of the thermal oxide film is preferably 200 to 500 angstroms, and a metal element is added to the amorphous silicon film after the step of forming the amorphous silicon film. Is preferably added at a concentration of 1 × 10 ^{16 to} 5 × 10 ¹⁹ atoms / cm ³ . Further, a metal element is preferably used for forming the crystalline silicon film, and the metal element is at least one selected from Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Cu, and Au. These elements can be used. This also applies to the case of the aforementioned invention.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, of course, this invention is not limited to these Examples. First, as Examples 1 to 3, Examples using the metal element and showing the effect of removing or reducing the metal element in the crystalline silicon film crystallized by the action of the metal element and the halogen concentration In the following, examples corresponding to the inventions (1) to (33) are sequentially described.

Example 1
FIG. 16 shows the result of measuring the concentration distribution of nickel element in the film cross-sectional direction at the time when the thermal oxide film was formed after the amorphous silicon film was crystallized using nickel as the metal element. This measurement was performed by SIMS (secondary ion analysis method). The preparation process of the sample from which this measured value was obtained is as outlined below.

  A silicon oxide film having a thickness of 4000 angstroms was formed as a base film on a quartz substrate, and then an amorphous silicon film having a thickness of 500 angstroms was formed by low pressure thermal CVD. Next, nickel element was introduced into the amorphous silicon film using an aqueous solution of nickel acetate. Furthermore, it was crystallized by heat treatment at a temperature of 650 ° C. for 4 hours to obtain a crystalline silicon film. Thereafter, heat treatment was performed in an oxygen atmosphere at a temperature of 950 ° C. to form a 700 Å thick thermal oxide film.

As is apparent from FIG. 16, the nickel element is transferred from the crystalline silicon film (Poly-Si film) to the silicon oxide film (thermal oxide film) and is contained in the thermal oxide film. Further, the nickel element is relatively more in the crystalline silicon film than in the thermal oxide film, which is interpreted as a result of a large amount of O being incorporated into the thermal oxide film as SiO ₂ . In addition, the concentration of nickel element on the surface of the thermal oxide film is considered to be a measurement error affected by the surface condition due to surface irregularities or adsorbate, so it is not significant. Absent. For the same reason, some errors are included in the data near the interface.

Example 2
Next, as a method of forming the thermal oxide film, heat treatment is performed in an oxygen atmosphere containing 950 ° C. and 3% by volume of HCl, and the other processes are performed in the same manner as in the first embodiment with a thickness of 500 Å. A thermal oxide film was formed. FIG. 17 shows measurement data for the sample in this case. As is apparent from FIG. 17, the nickel concentration in the crystalline silicon film is further lowered, and instead the nickel concentration in the thermal oxide film is relatively increased. This means that nickel element was further sucked out (that is, gettered) into the formed thermal oxide film.

  The difference between FIG. 16 and FIG. 17 is only whether or not HCl is contained in the atmosphere when forming the oxide film. Therefore, it can be concluded that the above-described gettering effect is greatly related to HCl in addition to oxygen. Further, since the gettering effect due to H (hydrogen) which is a component of HCl has not been confirmed, the gettering effect as shown in the difference between FIG. 16 and FIG. 17 is more accurately caused by the action of Cl (chlorine). You can see that

  By removing the thermal oxide film gettered with the nickel element, a crystalline silicon film having a low nickel concentration can be obtained. Further, FIG. 18 is a graph showing the concentration distribution of Cl element in a sample manufactured under the same conditions as the sample from which the data of FIG. 17 was obtained. As apparent from FIG. 18, the Cl element is concentrated near the interface between the crystalline silicon film and the thermal oxide film.

Example 3
In this third embodiment, an amorphous silicon film formed by a plasma CVD method is used instead of the amorphous silicon film which is the starting film of the crystalline silicon film from which the data described in the first to second embodiments is obtained. This is an example in the case where a film is used, and other manufacturing conditions are the same as those in Example 1. The amorphous silicon film formed by the plasma CVD method is different in film quality from the amorphous silicon film formed by the low pressure thermal CVD method. It will be different.

  First, FIG. 19 shows sample measurement data when the thermal oxide film is formed in an oxygen atmosphere at a temperature of 950.degree. As can be seen from FIG. 19, the nickel element has also moved to the thermal oxide film, but the nickel element is present at a relatively high concentration in the crystalline silicon film. Although the introduction conditions of nickel are the same, the nickel concentration in the crystalline silicon film is higher than that in FIG. This is presumably because the amorphous silicon film formed by the plasma CVD method is not dense and has many defects, so that nickel element is more easily diffused into the film.

  Looking at the above facts from another point of view, we can take another view as follows. That is, before applying the nickel acetic acid aqueous solution, in order to improve wettability, an extremely thin oxide film was formed on the surface of the amorphous silicon film by a UV (ultraviolet) oxidation method. There is a possibility that the difference is influenced by the difference in film quality of the underlying amorphous silicon film. In this case, since the amount of nickel element diffusing in the silicon film differs depending on the difference in film thickness, it can be considered that the influence appears in the difference between FIG. 16 and FIG.

  Further, FIG. 20 shows data when HCl is contained in an amount of 1% by volume with respect to oxygen as the atmosphere in forming the thermal oxide film. As is clear from FIG. 20, the nickel concentration in the crystalline silicon film is further reduced as compared with the data shown in FIG. Correspondingly, the nickel concentration in the thermal oxide film is increased.

  This fact means that the nickel element was gettered by the action of chlorine in the thermal oxide film. Thus, by forming a thermal oxide film in an oxidizing atmosphere containing chlorine, nickel elements present in the crystalline silicon film can be more effectively gettered in the thermal oxide film. Then, by removing the thermal oxide film gettered with nickel element, a crystalline silicon film with a low nickel concentration can be obtained.

  Further, the graph shown in FIG. 21 is a result of examining the chlorine concentration in a sample obtained under the same manufacturing conditions as the sample from which the data shown in FIG. 20 was obtained. As is clear from FIG. 21, chlorine is present in high concentration in the vicinity of the interface between the base film and the crystalline silicon film and in the vicinity of the interface between the crystalline silicon film and the thermal oxide film. FIG. 21 corresponds to FIG. 18, but the distribution of chlorine concentration is formed as shown in FIG. 21 because the amorphous silicon film as the starting film is formed by the plasma CVD method, and the film quality is It is presumed to be due to being not precise.

  Further, as is apparent from FIG. 20, in this case, it is recognized that the nickel concentration tends to be high near the interface between the base film and the crystalline silicon film. This is understood as a result of gettering of nickel toward the base film by the action of chlorine existing in the vicinity of the interface with the base film (or in the base film). Such a phenomenon is considered to be obtained even when a halogen element is added to the base film.

  As described above, the effects demonstrated in the first to third embodiments can be more effectively performed depending on the transition of the metal element to the thermal oxide film, the gettering conditions, and the like according to the present invention. Hereinafter, each Example corresponding to the inventions (1) to (33) will be described, including modifications and the like as appropriate.

Example 4
Example 4 is an example in which a crystalline silicon film is obtained on a glass substrate using nickel element. First, a crystalline silicon film having high crystallinity was obtained by the action of nickel element. Subsequently, it was formed on this crystalline silicon film by a thermal oxidation method. At this time, the nickel element remaining in the crystalline silicon film is gettered in the thermal oxide film. Next, as a result of the gettering, the thermal oxide film containing nickel element at a high concentration was removed. By doing so, a crystalline silicon film having high crystallinity and a low nickel element concentration was obtained on the glass substrate.

FIG. 22 is a diagram showing manufacturing steps in the fourth embodiment. First, a silicon oxynitride film 2 having a thickness of 3000 angstroms was formed on a Corning 1737 glass substrate (strain point: 667 ° C.) 1 as a base film. The silicon oxynitride film is formed using, for example, a plasma CVD method using silane, N ₂ O gas, and oxygen as source gases, or a plasma CVD method using TEOS gas and N ₂ O gas. However, the former was used here.

  This silicon oxynitride film has a function of suppressing diffusion of impurities from a glass substrate (a large amount of impurities are contained in the glass substrate as viewed at the semiconductor manufacturing level) in a later step. . Further, as the base film, a silicon oxide film can be used instead of the silicon oxynitride film. Note that a silicon nitride film is optimal for obtaining the maximum function of suppressing the diffusion of the impurities. However, the silicon nitride film is peeled off from the glass substrate due to stress, so that it is practical for a glass substrate. is not.

  Further, it is an important point that the base film 2 has a hardness as high as possible. This is concluded from the fact that in the durability test of the finally obtained thin film transistor, the harder the base film is harder (that is, the lower the etching rate), the higher the reliability. Although the reason is unknown in detail, it is presumably due to the effect of shielding impurities from the glass substrate during the manufacturing process of the thin film transistor.

  It is also effective to add a trace amount of a halogen element typified by chlorine in the base film 2. In this manner, a metal element that promotes crystallization of silicon present in the semiconductor layer can be gettered with a halogen element in a later step. In addition, it is effective to apply a hydrogen plasma treatment after forming the base film, and it is effective to perform the plasma treatment in an atmosphere in which oxygen and hydrogen are mixed. These treatments are effective in removing carbon components adsorbed on the surface of the base film and improving interface characteristics with a semiconductor film to be formed later.

Next, an amorphous silicon film 3 to be a crystalline silicon film later was formed to a thickness of 500 angstrom by a low pressure thermal CVD method. The reason why the low pressure CVD method is used here is that the crystalline silicon film obtained later is superior in film quality, specifically, the film quality is dense. As a method other than the low pressure thermal CVD method, a plasma CVD method or the like can be used. The amorphous silicon film produced here preferably has an oxygen concentration in the film of 5 × 10 ¹⁷ cm ⁻³ to 2 × 10 ¹⁹ cm ⁻³ . This is because oxygen plays an important role in a metal element gettering process that promotes crystallization of silicon, which is a subsequent process.

However, when the oxygen concentration is higher than the above concentration range, care must be taken because crystallization of the amorphous silicon film is inhibited. Further, the concentration of other impurities, for example, the concentration of nitrogen or carbon is preferably as low as possible. Specifically, the concentration needs to be 2 × 10 ¹⁹ cm ⁻³ or less. The thickness of the amorphous silicon film 3 here is 1600 angstroms. The film thickness of this amorphous film needs to be larger than the final required film thickness.

  When the amorphous silicon film 3 is crystallized only by heating, the film thickness of the starting film (amorphous silicon film) 3 is set to 800 Å to 5000 μm, preferably 1500 to 3000 Å. If it is thicker than this film thickness range, the film formation time becomes longer, which is uneconomical in terms of production cost. On the other hand, when the thickness is smaller than this range, the crystallization becomes non-uniform or the reproducibility of the process deteriorates. In this way, the state shown in FIG. Next, nickel element is introduced to crystallize the amorphous silicon film 3. Here, nickel element was introduced by applying a nickel acetate aqueous solution containing 10 ppm (in weight) of nickel to the surface of the amorphous silicon film 3.

  As a method for introducing nickel element, in addition to the method using a nickel salt solution as described above, a sputtering method, a CVD method, a plasma processing method, and an adsorption method can be used. Among these, the method using a solution is simple and useful in that the concentration of the metal element can be easily adjusted. Various nickel salts can be used as the nickel salt, and as the solvent, water, alcohols and other organic solvents, or a mixed solvent of water and an organic solvent can be used.

  In this example, the water film 4 was formed as shown in FIG. 22B by applying the nickel acetate solution as described above. In this state, excess solution was blown off using a spin coater (not shown). In this way, the nickel element is held in contact with the surface of the amorphous silicon film 3. In consideration of residual impurities in the subsequent heating step, it is preferable to use a solution containing a nickel salt that does not contain carbon, such as a nickel sulfate solution, instead of using a nickel acetate salt solution. This is because the nickel acetate salt solution contains carbon, which is feared to carbonize and remain in the film in the subsequent heating step. The amount of nickel element introduced can be adjusted by adjusting the concentration of nickel salt in the solution.

Next, in the state shown in FIG. 22C, heat treatment was performed at a temperature of 450 ° C. to 650 ° C. to crystallize the amorphous silicon film 3 to obtain a crystalline silicon film 5. This heat treatment is performed in a reducing atmosphere. Here, heat treatment was performed at a temperature of 620 ° C. for 4 hours in a nitrogen atmosphere containing 3% by volume of hydrogen. In this way, a crystalline silicon film 5 was obtained as shown in FIG. The reason why the atmosphere in the crystallization process by heat treatment is reduced is to prevent the formation of oxide during the heat treatment process. More specifically, nickel and oxygen react with each other. NiO _X is to suppress the undesirably formed on the surface of the film or within the film to.

  By the way, oxygen is combined with nickel in a later gettering step, and contributes greatly to the gettering of nickel. However, it has been found that the combination of oxygen and nickel in the crystallization stage inhibits crystallization. Therefore, in the crystallization step by heating, it is important to suppress the formation of oxides as much as possible. The oxygen concentration in the atmosphere in which the heat treatment for crystallization is performed is in the order of ppm, preferably 1 ppm or less.

  In addition, as a gas occupying most of the atmosphere in which the heat treatment for crystallization is performed, an inert gas such as nitrogen or argon, a mixed gas thereof, or the like can be used. Using. The lower limit of the heat treatment temperature for crystallization is preferably 450 ° C. or higher in view of the effect and reproducibility. On the other hand, the upper limit is preferably set to be equal to or lower than the strain point of the glass substrate to be used. In this example, a Corning 1737 glass substrate having a strain point of 667 ° C. is used. To the extent.

  In this regard, if a quartz substrate is used as the substrate, the heating temperature can be further increased to a temperature of about 900 ° C. or higher. In this case, a crystalline silicon film having higher crystallinity can be obtained, and a crystalline silicon film can be obtained in a shorter time. After obtaining the crystalline silicon film 5, the heat treatment was performed again. This heat treatment is performed to form a thermal oxide film containing nickel element. Here, this heat treatment was performed in an atmosphere of 100% oxygen.

  FIG. 22D is a diagram illustrating this heat treatment step. This step is a step for removing from the crystalline silicon film 5 the nickel element (other metal element that promotes the crystallization of silicon) intentionally mixed in the initial stage for crystallization. This heat treatment is performed at a temperature higher than the heat treatment performed for the above-described crystallization. This is an important condition for effective gettering of nickel element.

  This heat treatment is performed at a temperature of 550 to 1050 ° C., preferably 600 to 980 ° C. after satisfying the above conditions. This is because the effect cannot be obtained at 600 ° C. or lower, and conversely, if it exceeds 1050 ° C., the jig made of quartz is distorted or the apparatus is burdened (in this sense, it is 980 ° C. or lower). Preferably). Moreover, the upper limit of this heat processing temperature is restrict | limited by the strain point of the glass substrate to be used. When heat treatment is performed at a temperature equal to or higher than the strain point of the glass substrate to be used, care must be taken because the substrate is deformed.

  In this example, since a Corning 1737 glass substrate having a strain point of 667 ° C. is used, the heating temperature is set to 640 ° C. When heat treatment is performed under such conditions, a thermal oxide film 6 is formed as shown in FIG. Here, a heat treatment for 12 hours was performed to form a thermal oxide film 6 having a thickness of 200 angstroms. By forming the thermal oxide film 6, the thickness of the crystalline silicon film 3 becomes about 1500 angstroms. In this heat treatment, when the heating temperature is 600 ° C. to 750 ° C., the treatment time (heating time) is about 10 to 48 hours, typically 24 hours. When the heating temperature is 750 ° C. to 900 ° C., the treatment time is about 5 hours to 24 hours, typically 12 hours.

  When the heating temperature is in the range of 900 ° C. to 1050 ° C., the treatment time is about 1 hour to 12 hours, typically 6 hours. Of course, these processing times are appropriately set depending on the thickness of the oxide film to be obtained. In this step, nickel element is gettered in the thermal oxide film 6 to be formed. In this gettering, oxygen existing in the crystalline silicon film plays an important role in addition to the oxygen atmosphere. In other words, nickel oxide is formed by combining oxygen and nickel, and the nickel element is gettered into the thermal oxide film 6 in this form.

  As described above, when the concentration of oxygen is excessive, it becomes an element that inhibits the crystallization of the amorphous silicon film 3 in the crystallization step shown in FIG. However, as described above, its presence plays an important role in the nickel gettering process. Therefore, it is important to control the concentration of oxygen present in the amorphous silicon film as the starting film. Through this step, the nickel element in the crystalline silicon film 5 can be removed, or the concentration thereof can be lowered from the initial concentration.

  In the above process, since nickel element is gettered in the oxide film to be formed, the nickel concentration in the oxide film is naturally higher than that in other regions. Further, a tendency for nickel element to increase near the silicon film 5 side at the interface between the silicon film 5 and the oxide film 6 was observed. This is considered to be because the region where gettering is mainly performed is on the oxide film side in the vicinity of the interface between the silicon film and the oxide film. The reason why gettering proceeds in the vicinity of the interface is considered to be caused by the presence of stress and defects in the vicinity of the interface, and also by organic substances.

  After the formation of the thermal oxide film 6, the thermal oxide film 6 containing nickel at a high concentration was removed. The removal of the thermal oxide film 6 is performed by wet etching or dry etching using, for example, buffer hydrofluoric acid (other hydrofluoric acid-based etchant), but the former is applied here. Thus, as shown in FIG. 22E, a crystalline silicon film 7 having a reduced nickel content was obtained. In the vicinity of the surface of the obtained crystalline silicon film 7, a relatively high concentration of nickel element is contained. Therefore, the etching of the thermal oxide film 6 is further advanced, and the surface of the crystalline silicon film 7 is slightly changed. It is effective to over-etch.

Example 5
In Example 5, the crystalline silicon film was obtained by the heat treatment shown in FIG. 22C in the structure shown in Example 4, and then further irradiated with laser light to promote the crystallinity. An example is shown. Necessary when the temperature of the heat treatment shown in FIG. 22C is low or the treatment time is short, that is, when the heating temperature is limited or the heating time is limited due to a manufacturing process. Crystallinity may not be obtained. In such a case, the required high crystallinity can be obtained by annealing by laser light irradiation.

  The laser light irradiation in this case can have a wider range of allowable laser irradiation conditions and higher reproducibility than the case where the amorphous silicon film is directly crystallized. Irradiation with laser light may be performed after the step shown in FIG. Further, it is important that the amorphous silicon film 3 as a starting film formed in FIG. 22A has a thickness of 200 angstroms to 2000 angstroms. This is because the thinner the amorphous silicon film, the higher the annealing effect due to laser light irradiation.

  The laser beam to be used is not particularly limited, but preferably an ultraviolet laser beam, for example, an ultraviolet excimer laser is used. Specifically, a KrF excimer laser (wavelength 248 nm), a XeCl excimer laser (wavelength 308 nm), or the like can be used. In this example, a KrF excimer laser (wavelength 248 nm) was used. In addition, annealing can be performed by irradiating with strong light using an ultraviolet lamp or an infrared lamp instead of a laser beam.

Example 6
The sixth embodiment is an example in which an infrared lamp is used instead of the laser beam in the fifth embodiment. When infrared rays are used, the silicon film can be selectively heated without heating the glass substrate so much. Therefore, an effective heat treatment could be performed without causing thermal damage to the glass substrate.

Example 7
The seventh embodiment is an example in which Cu is used as the metal element for promoting the crystallization of silicon in the configuration shown in the fourth embodiment. In the case of copper element, as a solution for introducing Cu, for example, a solution of cupric acetate [Cu (CH ₃ COO) ₂ ] or cupric chloride (CuCl ₂ 2H ₂ O) may be used. In this example, an aqueous solution of cupric acetate [Cu (CH ₃ COO) ₂ ] was used.

Example 8
The eighth embodiment is an example in which a quartz substrate is used as the substrate 1 in the configuration shown in the fourth embodiment. In this embodiment, the thickness of the amorphous silicon film 3 serving as a starting film is set to 2000 angstroms. In addition, the heating temperature at the time of forming the thermal oxide film by the heat treatment shown in FIG. In this case, the formation of the oxide film is fast and the gettering effect cannot be sufficiently obtained, so the oxygen concentration in the atmosphere is lowered. Specifically, the oxygen concentration in the nitrogen atmosphere was set to 10% by volume.

  The processing time in this example was 300 minutes. Under such conditions, a thermal oxide film having a film thickness of about 500 angstroms can be obtained. At the same time, the time required for gettering can be earned. When heat treatment at 950 ° C. is performed in an atmosphere of 100% oxygen, a thermal oxide film having a thickness of 500 Å or more is obtained in about 30 minutes.

  In this case, nickel gettering cannot be performed sufficiently, so that nickel element remains in the crystalline silicon film 7 at a relatively high concentration. Therefore, it is preferable to form the thermal oxide film by adjusting the oxygen concentration and obtaining a sufficient time for obtaining a gettering effect as shown in this embodiment. When the thickness of the thermal oxide film and the formation temperature are changed as in this method, the time required for gettering the metal element can be set by adjusting the oxygen concentration of the atmosphere.

Example 9
The ninth embodiment is an example in which crystal growth in a form different from that of the fourth embodiment is performed. This embodiment relates to a method of performing crystal growth in a direction parallel to the substrate, called lateral growth, using a metal element that promotes crystallization of silicon. FIG. 23 is a view showing a manufacturing process of the ninth embodiment. First, a silicon oxynitride film having a thickness of 3000 angstroms was formed as a base film 9 on a Corning 1737 glass substrate 8 by low pressure thermal CVD. Of course, a quartz substrate may be used instead of the glass substrate.

  Next, an amorphous silicon film 10 serving as a starting film for the crystalline silicon film was formed to a thickness of 2000 angstroms by low pressure thermal CVD. As described above, the thickness of the amorphous silicon film is preferably 2000 angstroms or less. Note that a plasma CVD method or the like may be used instead of the low pressure thermal CVD method. Next, a silicon oxide film (not shown) was formed to a thickness of 1500 angstroms and patterned to form a mask indicated by reference numeral 11. This mask has an opening formed in a region indicated by 12. In the region where the opening 12 is formed, the amorphous silicon film 10 is exposed.

  The opening 12 has a rectangular shape elongated in the longitudinal direction from the depth of the drawing to the front. The width of the opening 12 is suitably 20 μm or more, and the length in the longitudinal direction may be arbitrarily determined. Here, the width is 30 μm and the length is 5 cm. And as shown in Example 4, after apply | coating the nickel acetate aqueous solution which contains 10 ppm of nickel elements by weight conversion, spin drying was performed using the spinner which is not illustrated, and the excess solution was removed. Thus, the state in which the nickel element was held as a solution in contact with the exposed surface of the amorphous silicon film 10 was realized as indicated by the dotted line 13 in FIG.

  Next, heat treatment was performed at a temperature of 640 ° C. for 4 hours in a nitrogen atmosphere containing 3% by volume of hydrogen and containing as little oxygen as possible. Then, crystal growth in a direction parallel to the substrate progressed as indicated by 14 in FIG. This crystal growth proceeds from the region of the opening 12 into which nickel element is introduced toward the periphery. This crystal growth in a direction parallel to the substrate is referred to as lateral growth or lateral growth in this specification.

  Under the conditions as in Example 9, this lateral growth can be performed over 100 μm or more. Thus, a crystalline silicon film 15 having a laterally grown region was obtained. In the region where the opening 12 is formed, crystal growth in the vertical direction called vertical growth proceeds from the surface of the silicon film toward the base interface. Next, the mask 11 which is a silicon oxide film for selectively introducing nickel element was removed. In this way, the state shown in FIG. In this state, the silicon film 15 includes a vertical growth region, a lateral growth region, and a region where the crystal growth does not reach (amorphous region).

  In this state, heat treatment at a temperature of 640 ° C. was performed for 12 hours in an oxygen atmosphere. In this step, the oxide film 16 containing nickel element at a high concentration is formed, and at the same time, the nickel element concentration in the silicon film 15 can be relatively reduced. Here, the thermal oxide film 16 is formed to a thickness of 200 angstroms. This thermal oxide film contains gettered nickel element at a high concentration. Further, since the thermal oxide film 16 is formed, the crystalline silicon film 15 has a thickness of about 2000 angstroms to about 1900 angstroms.

  Next, the thermal oxide film 16 containing nickel element at a high concentration was removed in the same manner as in Example 4. The crystalline silicon film in this state has a concentration distribution such that nickel element exists at a high concentration toward the surface of the crystalline silicon film. Therefore, after removing the thermal oxide film 16, it is useful to remove the region where nickel element exists at a high concentration by further etching the surface of the crystalline silicon film. That is, by etching the surface of the crystalline silicon film in which nickel element is present at a high concentration, a crystalline silicon film having a further reduced nickel element concentration can be obtained.

  Next, by patterning, a pattern 17 composed of a lateral growth region was formed as shown in FIG. Here, it is important that the pattern 17 does not have a vertical growth region, an amorphous region, and a lateral growth tip region. This is because the concentration of nickel element is relatively high in the tip region of the vertical growth and the horizontal growth, and the amorphous region in which the crystal growth does not reach has poor electrical characteristics. Thus, the concentration of the nickel element remaining in the pattern 17 can be made lower than that in the case shown in the fourth embodiment.

This is also due to the fact that the concentration of the metal element contained in the lateral growth region is low in the first place. Specifically, the concentration of the nickel element in the pattern 17 composed of the lateral growth region can be easily set to the order of 10 ¹⁷ cm ⁻³ or less. Further, when the thin film transistor is formed by using the lateral growth region, it is higher than that in the case of using the vertical growth region (in the case of Example 4, the entire surface grows vertically) as shown in the fourth embodiment. A semiconductor device having mobility can be obtained.

  Note that after the pattern shown in FIG. 23E is formed, it is useful to further perform an etching process to remove nickel elements present on the pattern surface. Further, it is not effective to form a thermal oxide film for gettering after the pattern 17 is formed. In this case, the gettering effect by the thermal oxide film can be surely obtained, but the etching of the base film also proceeds at the time of removing the thermal oxide film, so that the underside of the crystalline silicon film formed in the island shape can be obtained. This is because the etching proceeds.

  Such a state causes a disconnection of the wiring and a malfunction of the element later. In this embodiment, the thermal oxide film 18 is formed after the pattern 17 is formed. If the thermal oxide film 18 constitutes a thin film transistor, it is a part that will later become a part of the gate insulating film and is accompanied by the gettering effect, but is not intended for removal.

Example 10
Embodiment 10 is an example in which a thin film transistor disposed in a pixel region of an active matrix liquid crystal display device or an active matrix EL display device is manufactured using the crystalline silicon film according to the present invention. FIG. 24 is a view showing a manufacturing process of the tenth embodiment.

  First, a crystalline silicon film is formed on a glass substrate by the steps shown in Example 4 or Example 9. In this example, the step of Example 4 was used. The crystalline silicon film obtained here was patterned to obtain the state shown in FIG. In FIG. 24A, reference numeral 20 is a glass substrate, 21 is a base film, and 22 is an active layer made of a crystalline silicon film. After obtaining the state shown in FIG. 24A, plasma treatment was performed in a reduced pressure atmosphere in which oxygen and hydrogen were mixed. This plasma was formed by high frequency discharge.

  By the plasma treatment, organic substances present on the exposed surface of the active layer 22 are removed. Precisely, the organic substance adsorbed on the surface of the active layer is oxidized by oxygen plasma, and the oxidized organic substance is reduced and vaporized there by hydrogen plasma. In this way, organic substances present on the exposed surface of the active layer 22 are removed. This removal of organic matter is very effective in suppressing the presence of fixed charges on the surface of the active layer 22. Fixed charges resulting from the presence of organic substances hinder the operation of the device and cause instability of characteristics, and it is very useful to reduce the presence thereof.

After removal of the organic matter, thermal oxidation was performed in an oxygen atmosphere at a temperature of 640 ° C. to form a 100 angstrom thermal oxide film 19. This thermal oxide film has high interface characteristics with the semiconductor layer, and will later constitute a part of the gate insulating film. In this way, the state shown in FIG. Thereafter, a silicon oxynitride film 23 constituting a gate insulating film was formed to a thickness of 1000 angstroms. As a film forming method, a plasma CVD method using a mixed gas of oxygen, silane, and N ₂ O, or a plasma CVD method using a mixed gas of TEOS and N ₂ O can be used. Was used. The silicon oxynitride film 23 functions as a gate insulating film together with the thermal oxide film 19.

  In addition, it is effective to include a halogen element in the silicon oxynitride film 23. That is, by fixing the nickel element by the action of the halogen element, the gate insulating film is insulated by the influence of the nickel element existing in the active layer 22 (the same applies to other metal elements that promote crystallization of silicon). It can prevent that the function as a film | membrane falls. The silicon oxynitride film has a significance that it is difficult for a metal element to enter the gate insulating film due to its dense film quality. When a metal element penetrates into the gate insulating film, the function as the insulating film is lowered, which causes instability and variations in characteristics of the thin film transistor. Note that a commonly used silicon oxide film can also be used as the gate insulating film.

  After forming a silicon oxynitride film 23 that functions as a gate insulating film, an aluminum film (not shown) that functions as a gate electrode later is formed by sputtering. This aluminum film contained 0.2% by weight of scandium. The reason why scandium is contained in the aluminum film is to suppress generation of hillocks and whiskers in the subsequent process. Here, hillocks and whiskers mean that when heating is performed, abnormal growth of aluminum occurs and needle-like or stab-like protrusions are formed.

  After forming the aluminum film, a dense anodic oxide film (not shown) was formed. This anodic oxide film was formed by using an ethylene glycol solution containing 3% by weight of tartaric acid as an electrolytic solution. In this electrolytic solution, anodization is performed using the aluminum film as an anode and platinum as a cathode, whereby an anodized film having a dense film quality is formed on the surface of the aluminum film. The film thickness of the anodic oxide film having a dense film quality (not shown) is about 100 angstroms. This anodic oxide film has a role of improving adhesion with a resist mask to be formed later. The film thickness of the anodic oxide film can be controlled by the applied voltage during anodic oxidation.

  Next, a resist mask 25 was formed, and the aluminum film was patterned into a pattern indicated by 24. In this way, the state shown in FIG. Here, anodic oxidation is performed again. Here, a 3% by weight oxalic acid aqueous solution was used as the electrolytic solution. In this electrolytic solution, a porous anodic oxide film indicated by reference numeral 27 is formed by performing anodization using the aluminum pattern 26 as an anode. In this step, the anodic oxide film 27 is selectively formed on the side surface of the aluminum pattern because the resist mask 25 having high adhesion exists on the upper portion.

  This anodic oxide film can be grown to a thickness of several μm. Here, the film thickness was set to 6000 angstroms. The growth distance can be controlled by the anodic oxidation time. Next, the resist mask 25 was removed, and a dense anodic oxide film was formed again. That is, the anodic oxidation using the ethylene glycol solution containing 3% by weight of tartaric acid as an electrolytic solution was performed again. Then, an anodic oxide film having a dense film quality was formed as indicated by reference numeral 28 because the electrolytic solution entered the porous anodic oxide film 27.

  The film thickness of the dense anodic oxide film 28 was 1000 angstroms. The film thickness was controlled by adjusting the applied voltage. The exposed silicon oxynitride film 23 and thermal oxide film 19 were etched. Dry etching was used for this etching. Then, the porous anodic oxide film 27 was removed using a mixed acid obtained by mixing acetic acid, nitric acid and phosphoric acid. In this way, the state shown in FIG.

  After obtaining the state shown in FIG. 24D, impurity ions were implanted. Here, in order to fabricate an N-channel thin film transistor, P (phosphorus) ions are implanted by a plasma doping method. In this step, regions (30 and 34) to be heavily doped and regions (31 and 33) to be lightly doped are formed. This is because a part of the remaining silicon oxide film 29 functions as a semi-transmissive mask and a part of the implanted ions is shielded there.

  Next, the region into which the impurity ions were implanted was activated by laser light irradiation. In addition, it can replace with a laser beam and can also perform by irradiation of a strong light. Thus, the source region 30, the channel forming region 32, the drain region 34, and the low concentration impurity regions 31 and 33 are formed in a self-aligned manner. Here, what is indicated by reference numeral 33 in FIG. 24D is a region referred to as an LDD (lightly doped drain) region. When the film thickness of the dense anodic oxide film 28 is increased to 2000 angstroms or more, an offset gate region can be formed outside the channel formation region 32 depending on the film thickness.

  Also in this embodiment, the offset gate region is formed, but since its size is small, the contribution due to its existence is small, and the drawing becomes complicated, so it is not shown in FIG. . Next, a silicon oxide film, a silicon nitride film, or a stacked film thereof is formed as the interlayer insulating film 35. Here, a silicon oxide film was used. Note that the interlayer insulating film may be formed by forming a layer made of a resin material over a silicon oxide film or a silicon nitride film. Next, contact holes were formed, and a source electrode 36 and a drain electrode 37 were formed. Thus, the thin film transistor shown in FIG. 24E was completed.

Example 11
The eleventh embodiment relates to a method for forming the gate insulating film 23 in the configuration shown in the tenth embodiment. When a quartz substrate or a glass substrate with high heat resistance is used as the substrate, a thermal oxidation method can be applied as a method for forming the gate insulating film. The thermal oxidation method can make the film quality dense and is useful in obtaining a thin film transistor having stable characteristics. In other words, an oxide film formed by a thermal oxidation method is dense as an insulating film and can reduce the movable charges existing therein, and thus is one of the optimum gate insulating films.

In this embodiment, as a method for forming the thermal oxide film, heat treatment was performed in an oxidizing atmosphere at a temperature of 950 ° C. At this time, it is effective to mix HCl or the like in the oxidizing atmosphere. By doing in this way, the metal element which exists in an active layer can be fixed simultaneously with formation of a thermal oxide film. It is also effective to mix a N ₂ O gas in an oxidizing atmosphere to form a thermal oxide film containing a nitrogen component. Here, if the mixing ratio of N ₂ O gas is optimized, it is possible to obtain a silicon oxynitride film by a thermal oxidation method. In the case of this embodiment, it is not necessary to form the thermal oxide film 19 in particular, and the thermal oxide film 19 is not formed in this embodiment.

Example 12
Example 12 is an example in which a thin film transistor was manufactured by a process different from the processes shown in Examples 10 to 11. FIG. 25 is a diagram showing a manufacturing process of this example. First, a crystalline silicon film is formed on a glass substrate by the process shown in Example 4 or Example 5. Here, the crystalline silicon film was formed according to the process of Example 4. Next, by patterning it, the state shown in FIG. 25 (A) was obtained.

  Thereafter, plasma treatment was performed in a mixed reduced pressure atmosphere of oxygen and hydrogen. In the state shown in FIG. 25A, 39 is a glass substrate, 40 is a base film, and 41 is an active layer composed of a crystalline silicon film. Reference numeral 38 denotes a thermal oxide film formed again after removing the thermal oxide film for gettering. After obtaining the state shown in FIG. 25A, a silicon oxynitride film 42 constituting a gate insulating film was formed to a thickness of 1000 angstroms.

As a film formation method, a plasma CVD method using a mixed gas of oxygen, silane, and N ₂ O, or a plasma CVD method using a mixed gas of TEOS and N ₂ O can be applied. A mixed gas with N ₂ O was used. The silicon oxynitride film 42 and the thermal oxide film 38 constitute a gate insulating film. Note that a silicon oxide film can be used instead of the silicon oxynitride film. After forming the silicon oxynitride film 42 that functions as a gate insulating film, an aluminum film (not shown) that functions as a gate electrode later was formed by sputtering. This aluminum film contained 0.2% by weight of scandium.

  After forming the aluminum film, a dense anodic oxide film (not shown) was formed. This anodic oxide film was formed using an ethylene glycol solution containing 3% by weight of tartaric acid as an electrolytic solution. That is, in this electrolytic solution, an anodic oxidation film having a dense film quality is formed on the surface of the aluminum film by performing anodization using the aluminum film as an anode and platinum as a cathode. The film thickness of this anodic oxide film having a dense film quality is about 100 angstroms. This anodic oxide film has a role of improving adhesion with a resist mask to be formed later. The film thickness of the anodic oxide film can be controlled by adjusting the applied voltage during anodic oxidation.

  Next, a resist mask 43 was formed, and the aluminum film was patterned into a pattern indicated by 44. Next, anodic oxidation was performed again here. In this anodic oxidation, a 3% by weight oxalic acid aqueous solution was used as an electrolytic solution. In this electrolytic solution, a porous anodic oxide film denoted by reference numeral 45 is formed by performing anodization using the aluminum pattern 44 as an anode.

  In this step, the anodic oxide film 45 is selectively formed on the side surface of the aluminum pattern because the resist mask 43 having high adhesion exists on the upper portion. This anodic oxide film can be grown to a thickness of several μm. Here, the film thickness was set to 6000 angstroms. The growth distance can be controlled by adjusting the anodic oxidation time.

  Next, after removing the resist mask 43, a dense anodic oxide film was formed again. That is, the anodic oxidation using the ethylene glycol solution containing 3% by weight of tartaric acid as an electrolytic solution was performed again. Then, from the relationship that the electrolytic solution enters (invades) into the porous anodic oxide film 45, an anodic oxide film having a dense film quality is formed as indicated by reference numeral 46 in FIG.

  Here, the first impurity ions were implanted. This step may be performed at that time after the resist mask 43 is removed. By this impurity ion implantation, a source region 47 and a drain region 49 are formed. Impurity ions are not implanted into the 48 region. Next, the porous anodic oxide film 45 was removed using a mixed acid obtained by mixing acetic acid, nitric acid and phosphoric acid. Thus, the state shown in FIG.

  After obtaining the state shown in FIG. 25D, impurity ions were implanted again. This impurity ion is performed under the condition of light doping rather than the initial impurity ion implantation condition. In this step, lightly doped regions (50 and 51) are formed, and a region indicated by reference numeral 52 in FIG. 25D is a channel formation region. Next, the region into which the impurity ions were implanted was activated by irradiating intense light with an ultraviolet lamp. Note that laser light may be used instead of strong light. Thus, the source region 47, the channel formation region 52, the drain region 49, and the low concentration impurity regions 50 and 51 are formed in a self-aligned manner.

  Here, the region denoted by reference numeral 51 in FIG. 25D is a region called an LDD (lightly doped drain) region. Next, a silicon oxide film, a silicon nitride film, or a laminated film thereof is formed as the interlayer insulating film 53. Here, a silicon nitride film is used. Note that the interlayer insulating film may be formed by forming a layer made of a resin material over a silicon oxide film or a silicon nitride film. Thereafter, contact holes were formed, and a source electrode 54 and a drain electrode 55 were formed. Thus, the thin film transistor shown in FIG. 25E was completed.

Example 13
Example 13 is an example in which an N-channel thin film transistor and a P-channel thin film transistor are configured to be complementary. The structure shown in this embodiment can be used for various thin film integrated circuits integrated on an insulating surface, for example, and can be used for a peripheral drive circuit of an active matrix liquid crystal display device, for example.

  FIG. 26 is a diagram showing manufacturing steps of Example 13. First, as shown in FIG. 26A, a silicon oxide film or a silicon oxynitride film is formed as a base film 58 over a glass substrate 57. Of these, a silicon oxynitride film is preferably used, but a silicon oxynitride film is used here. Next, an amorphous silicon film (not shown) is formed by a plasma CVD method, a low pressure thermal CVD method, or the like. Here, the amorphous silicon film is formed by a low pressure thermal CVD method.

  Further, the amorphous silicon film was transformed into a crystalline silicon film by the same method as shown in Example 4, and then nickel element gettering was performed by forming a thermal oxide film. Next, plasma treatment was performed in a mixed atmosphere of oxygen and hydrogen, and the obtained crystalline silicon film was patterned to obtain active layers (59 and 60). Further, a thermal oxide film 56 constituting a gate insulating film was formed.

  After obtaining the state shown in FIG. 26A, a silicon oxynitride film 61 was formed. When quartz is used as the substrate, it is desirable to form the gate insulating film with only the thermal oxide film using the above-described thermal oxidation method. Next, an aluminum film (not shown) for forming the gate electrode was formed to a thickness of 4000 angstroms. As the film other than the aluminum film, a metal that can be anodized, such as tantalum, can be used. After forming the aluminum film, an extremely thin dense anodic oxide film was formed on the surface by the method described above.

  Next, after placing a resist mask (not shown) on the aluminum film and patterning the aluminum film, anodization was performed using the obtained aluminum pattern as an anode to form porous anodic oxide films (64 and 65). Formed. The thickness of the porous anodic oxide film was 5000 angstroms. Further, anodic oxidation was performed again under the conditions for forming a dense anodic oxide film to form dense anodic oxide films (66 and 67). Here, the dense anodic oxide films 66 and 67 have a thickness of 800 angstroms. In this way, the state shown in FIG.

  Further, the exposed silicon oxide film 61 and the thermal oxide film 56 were removed by dry etching to obtain the state shown in FIG. Thereafter, the porous anodic oxide films 64 and 65 were removed using a mixed acid obtained by mixing acetic acid, nitric acid and phosphoric acid. In this way, the state shown in FIG. Here, resist masks were alternately arranged, and P (phosphorus) ions were implanted into the left thin film transistor and B (boron) ions were implanted into the right thin film transistor.

  By implantation of these impurity ions, a source region 70 and a drain region 73 having a high concentration N-type were formed in a self-aligned manner. Further, a weak N-type region 71 doped with P ions at a low concentration was formed at the same time, and a channel forming region 72 was formed at the same time. The reason why the weak N-type region indicated by reference numeral 71 is formed is that the remaining gate insulating film 68 exists. That is, P ions that have passed through the gate insulating film 68 are partially shielded by the gate insulating film 68.

  Further, by the same principle and method, the source region 77 and the drain region 74 having strong P-type are formed in a self-alignment manner, the low-concentration impurity region 76 is simultaneously formed, and the channel formation region 75 is simultaneously formed. . If the dense anodic oxide films 66 and 67 are as thick as 2000 angstroms, for example, the offset gate region can be formed in contact with the channel formation region with that thickness.

  In the case of the present embodiment, since the dense anodic oxide films 66 and 67 are as thin as 1000 angstroms or less, their presence can be ignored. Then, laser light or strong light irradiation is performed to anneal the region into which the impurity ions are implanted. Here, irradiation is performed with an infrared lamp. Next, as shown in FIG. 26E, a silicon nitride film 78 and a silicon oxide film 79 were formed as interlayer insulating films, and the respective film thicknesses were set to 1000 angstroms. In this case, the silicon oxide film 79 may not be formed.

  Here, the thin film transistor is covered with the silicon nitride film. Since the silicon nitride film is dense and has good interface characteristics, the reliability of the thin film transistor can be improved with such a structure. Further, an interlayer insulating film 80 made of a resin material is formed by a spin coating method. Here, the thickness of the interlayer insulating film 80 is 1 μm. Next, contact holes were formed to form a source electrode 81 and a drain electrode 82 of the left N-channel thin film transistor. At the same time, a source electrode 83 and a drain electrode 82 of the right thin film transistor were formed. Here, the drain electrodes 82 are arranged in common. In this way, the state shown in FIG.

  As described above, a thin film transistor circuit having a complementary CMOS structure can be formed. In the structure shown in this example, a structure in which the thin film transistor was covered with a nitride film and further covered with a resin material was obtained. This configuration can be made highly durable such that mobile ions and moisture do not easily enter. Further, when a multilayer wiring is formed, it is possible to prevent a capacitor from being formed between the thin film transistor and the wiring.

Example 14
This Example 14 relates to a structure in which a region that can be regarded as a single crystal or substantially a single crystal is formed by further irradiating the crystalline silicon film obtained in Example 4 or Example 5 with laser light. It is an example.

  First, as shown in Example 4, a crystalline silicon film was obtained by utilizing the action of nickel element. Next, the film was irradiated with a KrF excimer laser to further promote its crystallinity. At this time, a heat treatment at a temperature of 450 ° C. or higher was used in combination, and the laser light irradiation conditions were further optimized, thereby forming a region that can be regarded as a single crystal or substantially a single crystal.

The film that greatly promotes crystallization by such a method has an electron spin density measured by ESR of 3 × 10 ¹⁷ cm ⁻³ or less, and the nickel element concentration is 3 × as the lowest value measured by SIMS. It has 10 ¹⁷ cm ⁻³ or less, and further has a region that can be regarded as a single crystal. In addition, there is substantially no grain boundary in this region, and high electrical characteristics comparable to those of a single crystal silicon wafer can be obtained.

In addition, the region that can be regarded as a single crystal contains hydrogen at 5 atomic% or less to about 1 × 10 ¹⁵ cm ⁻³ . This value was clarified by measurement by SIMS (secondary ion analysis method). By manufacturing a thin film transistor using such a single crystal or a region that can be regarded as a single crystal, a semiconductor device comparable to a MOS transistor manufactured using a single crystal wafer can be obtained.

Example 15
Example 15 shows an example in which nickel element is directly introduced into the surface of the base film in the step shown in Example 4. In this case, the nickel element is held in contact with the lower surface of the amorphous silicon film. In this embodiment, the nickel element is introduced after the formation of the base film, and the nickel element (the metal element) is first held in contact with the surface of the base film. As a method for introducing the nickel element, in addition to a method using a solution, a sputtering method, a CVD method, or an adsorption method can be used.

Example 16
In Example 16, a crystalline silicon film was obtained on a glass substrate using nickel element. In this embodiment, a crystalline silicon film having high crystallinity was first formed by the action of nickel element. Next, an oxide film containing a halogen element was formed on the crystalline silicon film by a thermal oxidation method. At this time, nickel element remaining in the obtained crystalline silicon film is gettered into the thermal oxide film by the action of oxygen and halogen elements.

  Next, as a result of the gettering, the thermal oxide film containing nickel element at a high concentration was removed. By doing so, a crystalline silicon film having a high crystallinity and a low nickel element concentration can be obtained on the glass substrate. FIG. 27 is a diagram showing a manufacturing process in this example.

First, a silicon oxynitride film 85 having a thickness of 3000 angstroms was formed as a base film on a Corning 1737 glass substrate (strain point 667 ° C.) 84. The silicon oxynitride film was formed by a plasma CVD method using silane, N ₂ O gas, and oxygen as source gases. This film formation may be performed using, for example, a plasma CVD method using TEOS gas and N ₂ O gas.

  The silicon oxynitride film has a function of suppressing diffusion of impurities from the glass substrate (a large amount of impurities are contained in the glass substrate as viewed from the manufacturing level of the semiconductor) in a later step. In order to obtain the maximum function of suppressing the diffusion of impurities, a silicon nitride film is optimal. However, since the silicon nitride film is peeled off from the glass substrate due to stress, It is not practical in some cases. A silicon oxide film can also be used as the base film.

  Here, it is important to make the base film 85 as hard as possible. This is concluded from the fact that in the durability test of the finally obtained thin film transistor, the harder the base film is harder (that is, the lower the etching rate), the higher the reliability. Note that the reason is considered to be due to the shielding effect of impurities from the glass substrate during the manufacturing process of the thin film transistor.

  In addition, it is effective to add a trace amount of a halogen element typified by chlorine in the base film 85. In this manner, a metal element that promotes crystallization of silicon present in the semiconductor layer can be gettered with a halogen element in a later step. In addition, it is effective to add a hydrogen plasma treatment after forming the base film. In addition, it is effective to perform plasma treatment in an atmosphere in which oxygen and hydrogen are mixed. This is effective in removing the carbon component adsorbed on the surface of the base film and improving the interface characteristics with the semiconductor film to be formed later.

  Next, an amorphous silicon film 86, which later becomes a crystalline silicon film, was formed to a thickness of 500 angstrom by a low pressure thermal CVD method. The reason why the low pressure thermal CVD method is used is that the crystalline silicon film obtained later is superior in film quality, and specifically, the film quality is dense. As a method other than the low pressure thermal CVD method, a plasma CVD method or the like can be used.

The amorphous silicon film produced here preferably has an oxygen concentration in the film of 5 × 10 ¹⁷ cm ⁻³ to 2 × 10 ¹⁹ cm ⁻³ . This is because oxygen plays an important role in the process of later gettering a metal element that promotes crystallization of silicon. However, when the oxygen concentration is higher than the above concentration range, care must be taken because crystallization of the amorphous silicon film is inhibited. Further, other impurity concentrations, for example, nitrogen and carbon impurity concentrations should be as low as possible. Specifically, the concentration needs to be 2 × 10 ¹⁹ cm ⁻³ or less.

  In this embodiment, the amorphous silicon film 86 has a thickness of 1600 angstroms. As will be described later, this film thickness needs to be larger than the film thickness that is finally required. When the amorphous silicon film 86 is crystallized only by heating, the film thickness of the starting film (amorphous silicon film) 86 is set to 800 Å to 5000 μm, preferably 1500 to 3000 Å. If it is thicker than this film thickness range, the film formation time becomes longer, which is uneconomical in terms of production cost. On the other hand, when the thickness is smaller than this range, crystallization becomes non-uniform or process reproducibility becomes poor. In this way, the state shown in FIG.

  Next, nickel element was introduced to crystallize the amorphous silicon film 86. Here, nickel element was introduced by applying a nickel acetate aqueous solution containing 10 ppm (weight conversion) of nickel to the surface of the amorphous silicon film 86. As a method for introducing nickel element, in addition to the method using the above solution, sputtering method, CVD method, plasma treatment or adsorption method can be used. Among these, the method using the above solution is useful in that it is simple and the concentration of the metal element can be easily adjusted.

  By applying the nickel acetate aqueous solution, a water film (liquid film) 87 is formed as shown in FIG. In this state, excess solution was blown off using a spin coater (not shown). Thus, the nickel element was held in contact with the surface of the amorphous silicon film 86. In view of residual impurities in the subsequent heating step, for example, nickel sulfate is preferably used instead of nickel acetate. This is because the nickel acetate salt contains carbon, which is feared to carbonize and remain in the film in the subsequent heating step. The amount of nickel element introduced can be adjusted by adjusting the concentration of nickel salt in the solution.

  Next, in the state shown in FIG. 27C, heat treatment is performed at a temperature of 450 ° C. to 650 ° C. for crystallization. This heat treatment is performed in a reducing atmosphere. Here, heat treatment was performed at a temperature of 620 ° C. for 4 hours in a nitrogen atmosphere containing 3% by volume of hydrogen. Thus, the amorphous silicon film 86 was crystallized to obtain a crystalline silicon film 88.

The reason why the atmosphere is reduced in the crystallization step by the heat treatment is to prevent the formation of oxides during the heat treatment step. More specifically, the reaction with nickel and oxygen, because the NiO _X is prevented from undesirably formed on the surface of the film or within the film.

  Oxygen combines with nickel in a later gettering step and contributes greatly to nickel gettering. However, it has been found that the combination of oxygen and nickel in the crystallization stage inhibits crystallization. Therefore, in the crystallization process by heating, it is important to suppress the formation of oxides as much as possible.

  Here, the oxygen concentration in the atmosphere in which the heat treatment for crystallization is performed needs to be on the order of ppm, preferably 1 ppm or less. Further, as a gas occupying most of the atmosphere in which the heat treatment for crystallization is performed, not limited to nitrogen, an inert gas such as argon or a mixed gas thereof can be used. The lower limit of the heat treatment temperature for crystallization is preferably 450 ° C. or higher in view of the effect and reproducibility. Further, the upper limit is preferably set to be equal to or lower than the strain point of the glass substrate to be used. When a Corning 1737 glass substrate having a strain point of 667 ° C. is used as in this embodiment, the upper limit is approximately Set to 650 ° C.

  In this regard, when a material having higher heat resistance such as a quartz substrate is used as the substrate, the substrate can be formed at a temperature of up to about 1100 ° C. (preferably up to about 1050 ° C.). In this case, a crystalline silicon film having higher crystallinity can be obtained, and a crystalline silicon film can be obtained in a shorter time. Thus, a crystalline silicon film 88 was formed as shown in FIG.

  After obtaining the crystalline silicon film 88, the heat treatment was performed again. This heat treatment is performed to form a thermal oxide film containing a halogen element. Here, this heat treatment was performed in an atmosphere containing a halogen element. This step is a step for removing nickel element intentionally mixed in the initial stage for crystallization from the crystalline silicon film 88.

  This heat treatment is preferably performed at a higher temperature than the heat treatment performed for the above-described crystallization. This is an important condition for effectively performing gettering of nickel element. Note that this heat treatment may be performed at the same temperature as the heat treatment performed for crystallization, but is more effective at a higher temperature, and higher quality crystals can be obtained.

  This heat treatment is performed at a temperature of 550 to 1100 ° C., preferably about 700 to 1050 ° C., more preferably 800 to 980 ° C. after satisfying the above conditions. This is because the effect is small when the temperature is lower than 600 ° C., and the temperature exceeding 1050 ° C. is because a jig made of quartz is distorted or a load is applied to the apparatus (in this sense, 980 ° C. or lower). It is preferable, but in the case of using a more heat-resistant jig, it can be carried out even at about 1100 ° C.). Further, the upper limit of the heat treatment temperature is also limited by the strain point of the substrate used. Care must be taken because the substrate is deformed if heat treatment is performed at a temperature equal to or higher than the strain point of the substrate to be used.

  Here, since a Corning 1737 glass substrate having a strain point of 667 ° C. is used, the heating temperature is set to 650 ° C. The atmosphere for the second heat treatment was an atmosphere containing 5% by volume of HCl in oxygen. HCl is preferably mixed at a ratio of 0.5 to 10% (volume%) with respect to oxygen. It should be noted that if the concentration is higher than this concentration, the surface of the film is roughened to the same degree of unevenness as the film thickness.

  By performing the heat treatment under such conditions, a thermal oxide film 89 containing chlorine is formed as shown in FIG. In this embodiment, a heat treatment for 12 hours was performed to form a thermal oxide film 89 having a thickness of 200 angstroms. By forming the thermal oxide film 89, the thickness of the crystalline silicon film 86 is about 1500 angstroms.

  In this heat treatment, when the heating temperature is 600 ° C. to 750 ° C., the treatment time (heating time) is 10 hours to 48 hours, typically 24 hours. When the heating temperature is 750 ° C. to 900 ° C., the treatment time is 5 hours to 24 hours, typically 12 hours. When the heating temperature is 900 ° C. to 1050 ° C., the treatment time is 1 hour to 12 hours, typically 6 hours. Of course, these processing times are appropriately set depending on the thickness of the oxide film to be obtained.

  In this step, nickel element is gettered out of the crystalline silicon film by the action of oxygen and the action of halogen element, particularly the action of halogen element. Here, nickel element is gettered in the natural oxide film 89 formed by the action of chlorine. In this gettering, oxygen present in the crystalline silicon film plays an important role. That is, gettering effect by chlorine acts on nickel oxide formed by combining oxygen and nickel, and gettering of nickel element proceeds effectively.

As described above, when the concentration of oxygen is excessive, it becomes an element that inhibits the crystallization of the amorphous silicon film 86 in the crystallization step shown in FIG. However, as mentioned above, its presence plays an important role in the nickel gettering process. Therefore, it is important to control the concentration of oxygen present in the amorphous silicon film as the starting film. In this embodiment, Cl is selected as the halogen element, and HCl is used as the introduction method. As the gas other than HCl, one kind or plural kinds of mixed gases selected from HF, HBr, Cl ₂ , F ₂ , and Br ₂ can be used. In addition to these, generally halogen hydrides can be used.

These gases have a content (capacity) in the atmosphere of 0.25 to 5% for HF, 1 to 15% for HBr, 0.25 to 5% for Cl ₂ , F ₂ 0.125 to 2.5% if it is preferable that 0.5 to 10% for Br _2. If the concentration is within the above range, a significant effect cannot be obtained. If the concentration exceeds the upper limit of the above range, the surface of the crystalline silicon film will be rough.

  Through this step, the nickel element concentration can be reduced to 1/10 or less of the initial concentration. This means that the nickel element can be reduced to 1/10 or less by the halogen element as compared with the case where no gettering by the halogen element is performed. This effect can be similarly obtained even when a metal element other than nickel that promotes crystallization of silicon is used. In the above process, since nickel element is gettered in the oxide film to be formed, the nickel concentration in the oxide film is naturally higher than that in other regions.

  Also, a tendency for the nickel element to increase near the interface between the crystalline silicon film 88 and the oxide film 89 is observed. It is considered that this is because the region where gettering is mainly performed is on the oxide film side in the vicinity of the interface between the crystalline silicon film and the oxide film. Further, it is considered that the gettering progresses in the vicinity of the interface between the two films due to the presence of stress and defects near the interface.

  Next, the oxide film 89 containing nickel at a high concentration was removed. The removal of the oxide film 89 can be performed by wet etching using buffer hydrofluoric acid or other hydrofluoric acid-based etchants or dry etching, but here, buffer hydrofluoric acid was used.

  Thus, as shown in FIG. 27E, a crystalline silicon film 90 with a reduced concentration of nickel contained was obtained. In this case, since the nickel element is contained in a relatively high concentration in the vicinity of the surface of the obtained crystalline silicon film 90, the etching is further advanced to slightly over-etch the surface of the crystalline silicon film 90. It is effective.

Example 17
In Example 17, in the structure shown in Example 16, after obtaining a crystalline silicon film by the heat treatment step shown in FIG. 27C, laser irradiation with a KrF excimer laser (wavelength 248 nm) was performed, This is an example in which the crystallinity is promoted. In this example, after the heat treatment step in FIG. 27C, laser beam irradiation is performed for annealing, and the other steps are the same as in Example 16 as shown in FIG. A crystalline silicon film 90 having a reduced nickel concentration was obtained.

  Necessary when the temperature of the heat treatment shown in FIG. 27C is low or the treatment time is short, that is, when the heating temperature is limited or the heating time is limited due to a manufacturing process. The crystallinity may not be obtained. In such a case, required high crystallinity can be obtained by performing annealing by laser light irradiation. In this case, the laser beam irradiation allows a wider range of allowable laser irradiation conditions and higher reproducibility than the case where the amorphous silicon film is directly crystallized. .

  The laser light irradiation is performed after the step shown in FIG. In addition, it is important that the amorphous silicon film 86 as a starting film formed in FIG. 27A has a thickness of 200 to 2000 angstroms. This is because the thinner the amorphous silicon film, the higher the annealing effect by laser light irradiation. The laser beam to be used is not particularly limited, but it is preferable to use an ultraviolet excimer laser. Specifically, for example, a KrF excimer laser (wavelength 248 nm) or a XeCl excimer laser (wavelength 308 nm) can be used. Also, annealing can be performed by irradiating strong light using, for example, an ultraviolet lamp instead of laser light.

Example 18
The eighteenth embodiment is an example in which an infrared lamp is used instead of the laser light in the seventeenth embodiment. In this example, after the heat treatment step of FIG. 27C, an infrared lamp was irradiated to perform annealing, and the other steps were performed in the same manner as in Example 16 as shown in FIG. A crystalline silicon film 90 having a reduced nickel concentration was obtained. When infrared rays are used, the silicon film can be selectively heated without heating the glass substrate so much. Therefore, an effective heat treatment can be performed without causing thermal damage to the glass substrate.

Example 19
Example 19 is an example in which Cu is used as the metal element for promoting crystallization of silicon in the configuration shown in Example 16. In this case, cupric acetate [Cu (CH ₃ COO) ₂ ], cupric chloride (CuCl ₂ 2H ₂ O), or the like may be used as a solution for introducing Cu. Copper [Cu (CH ₃ COO) ₂ ] was used. Other steps were performed in the same manner as in Example 16 to obtain a crystalline silicon film 90 with a reduced nickel concentration as shown in FIG.

Example 20
The present embodiment 20 is an example in which a quartz substrate is used as the substrate 84 in the configuration shown in the embodiment 16. In this embodiment, the thickness of the amorphous silicon film 86 serving as a starting film is 2000 angstroms. In addition, the heating temperature at the time of forming the thermal oxide film by the heat treatment shown in FIG. In this case, the formation of the oxide film is fast, and the effect of gettering cannot be obtained sufficiently, so the oxygen concentration in the atmosphere is lowered. Specifically, heat oxidation was performed in an atmosphere in which the oxygen concentration in the nitrogen atmosphere was 10% by volume and the HCl concentration relative to oxygen was 3% by volume.

  The processing time was 300 minutes. Under such conditions, a thermal oxide film having a film thickness of about 500 angstroms can be obtained. At the same time, the time required for gettering can be earned. If heat treatment is performed at 950 ° C. in an atmosphere containing 97% oxygen and 3% HCl, a thermal oxide film having a thickness of 500 Å can be obtained in about 30 minutes.

  In the above case, nickel gettering cannot be performed sufficiently, so that nickel element remains in the crystalline silicon film 90 at a relatively high concentration. Therefore, it is preferable to form the thermal oxide film by adjusting the oxygen concentration as in this embodiment, and taking time to obtain a sufficient gettering effect. By using this method, the time required for gettering can be set by adjusting the oxygen concentration of the atmosphere when the thickness and the formation temperature of the thermal oxide film are changed.

<< Example 21 >>
The present Example 21 is an example in which crystal growth of a form different from that of the Example 16 was performed. The present embodiment relates to a method of performing crystal growth in a direction parallel to a substrate, called lateral growth, using a metal element that promotes crystallization of silicon. FIG. 28 is a view showing a manufacturing process of the present Example 21.

  First, a silicon oxynitride film having a thickness of 3000 angstroms was formed as a base film 92 on a Corning 1737 glass substrate 91. The substrate may be a quartz substrate or the like. Next, an amorphous silicon film 93 serving as a starting film for the crystalline silicon film was formed to a thickness of 2000 angstroms by low pressure thermal CVD. As described above, the thickness of the amorphous silicon film is preferably 2000 angstroms or less. Note that a plasma CVD method may be used instead of the low pressure thermal CVD method.

  Next, a silicon oxide film (not shown) was formed to a thickness of 1500 angstroms and patterned to form a mask indicated by reference numeral 94. This mask has an opening formed in a region indicated by reference numeral 95. In the region where the opening 95 is formed, the amorphous silicon film 93 is exposed. The opening 95 has an elongated rectangular shape from the depth of the drawing to the front side (longitudinal direction). The width of the opening 95 is suitably 20 μm or more, and the length in the longitudinal direction may be arbitrarily determined. In this embodiment, the width of the opening 95 is 30 μm and the length in the longitudinal direction is 200 μm. .

  Next, in the same manner as in Example 16 described above, a nickel acetate solution containing 10 ppm of nickel element in terms of weight was applied. Furthermore, spin drying was performed using a spinner (not shown) to remove excess solution. Thus, a state in which the nickel acetate solution was held in contact with the exposed surface of the amorphous silicon film 93 was realized as indicated by a dotted line 96 in FIG.

  Next, heat treatment was performed at a temperature of 640 ° C. for 4 hours in a nitrogen atmosphere containing 3% by volume of hydrogen and containing as little oxygen as possible. Then, crystal growth proceeded in a direction parallel to the substrate as indicated by 97 in FIG. This crystal growth proceeds from the region of the opening 95 into which nickel element is introduced toward the periphery. This crystal growth in a direction parallel to the substrate is referred to as lateral growth or lateral growth in this specification.

  Under the conditions as shown in this embodiment, this lateral growth can be performed over 100 μm or more. Thus, a silicon film 98 having a laterally grown region was obtained. In the region where the opening 95 is formed, crystal growth in the vertical direction called vertical growth proceeds from the surface of the silicon film toward the base interface. Next, the mask 94 made of a silicon oxide film for selectively introducing nickel element was removed. In this way, the state shown in FIG. In this state, the silicon film 98 includes a vertical growth region, a lateral growth region, and a region where the crystal growth does not reach (amorphous state).

  In the above state, heat treatment at a temperature of 650 ° C. was performed for 12 hours in an oxygen atmosphere containing 3% by volume of HCl. In this step, an oxide film 99 containing nickel element at a high concentration is formed. At the same time, the nickel element concentration in the silicon film 98 can be relatively reduced. Here, a thermal oxide film denoted by reference numeral 99 was formed to a thickness of 200 angstroms. This thermal oxide film contains a high concentration of nickel element gettered by the action of oxygen and the action of chlorine, particularly the action of chlorine. In addition, by forming the thermal oxide film 99, the crystalline silicon film 98 has a thickness of about 1900 angstroms.

  Next, the thermal oxide film 99 containing nickel element at a high concentration was removed. The crystalline silicon film in this state has a concentration distribution such that nickel element exists at a high concentration toward the surface of the crystalline silicon film. Therefore, after removing the thermal oxide film 99, it is useful to further etch the surface of the crystalline silicon film to remove the region where the nickel element is present at a high concentration. That is, by etching the surface of the crystalline silicon film in which nickel element is present at a high concentration, a crystalline silicon film having a further reduced nickel element concentration can be obtained.

  Next, the pattern 100 which consists of a lateral growth area | region was formed by performing patterning. Here, it is important that the pattern 100 does not have a vertical growth region, an amorphous region, and a lateral growth tip region. This is because the concentration of nickel element is relatively high in the tip region of vertical growth and horizontal growth, and the amorphous region has poor electrical characteristics.

The concentration of the nickel element remaining in the pattern 100 composed of the laterally grown regions thus obtained can be made lower than that in the case shown in Example 16. This is also due to the fact that the concentration of the metal element contained in the lateral growth region is low in the first place. Specifically, the concentration of nickel element in the pattern 100 made of the lateral growth region can be easily set to the order of 10 ¹⁷ cm ⁻³ or less.

  Further, when the thin film transistor is formed by using the lateral growth region, it is higher than that in the case of using the vertical growth region (in the case of Example 16, the entire surface grows vertically) as shown in Example 16. A semiconductor device having mobility can be obtained. Note that it is useful to remove the nickel element existing on the pattern surface by further performing an etching process after the pattern shown in FIG.

  On the other hand, after patterning the crystalline silicon film into an island shape, it is not useful to perform thermal oxidation in an oxidizing atmosphere containing a halogen element and then remove the thermal oxide film. In this configuration, the gettering effect by the thermal oxide film can be surely obtained, but since the etching of the base film also proceeds when the thermal oxide film is removed, the etching is performed under the crystalline silicon film formed in the island shape. It is because it progresses so that it may go out.

  Such a state later becomes a cause of disconnection of wirings and malfunction of elements in the semiconductor device. Next, a thermal oxide film 101 was formed on the pattern 100 formed as described above. The thermal oxide film 101 becomes a part of the gate insulating film later when a thin film transistor is formed.

<< Example 22 >>
Example 22 is an example in which a thin film transistor disposed in a pixel region of an active matrix liquid crystal display device or an active matrix EL display device is manufactured using the crystalline silicon film according to the present invention. FIG. 29 is a diagram showing a manufacturing process of this example.

  First, a crystalline silicon film was formed on a glass substrate by the steps shown in Example 16 and Example 21, respectively. A thin film transistor was produced in the same manner based on each of them. Hereinafter, the case where the crystalline silicon film having the structure shown in the embodiment 16 is used will be described. However, the same applies to the case where the crystalline silicon film having the structure shown in the embodiment 21 is used. By patterning the crystalline silicon film, the state shown in FIG. 27A was obtained. In the state shown in FIG. 29A, 103 is a glass substrate, 104 is a base film, and 105 is an active layer made of a crystalline silicon film.

  Next, plasma treatment was performed in a reduced pressure atmosphere in which oxygen and hydrogen were mixed. This plasma was generated by high frequency discharge. By this plasma treatment, organic substances present on the exposed surface of the active layer 105 are removed. Precisely, the organic substance adsorbed on the surface of the active layer is oxidized by oxygen plasma, and the oxidized organic substance is reduced and vaporized by hydrogen plasma. In this way, organic substances present on the exposed surface of the active layer 105 were removed. This removal of organic substances is very effective in suppressing the presence of fixed charges on the surface of the active layer 105.

  Since the fixed charge resulting from the presence of the organic matter hinders the operation of the device or causes the instability of the characteristics, it is very useful to reduce the presence thereof. Next, after removing the organic matter, thermal oxidation was performed in an oxygen atmosphere at a temperature of 640 ° C. to form a 100 angstrom thermal oxide film 102. This thermal oxide film has high interface characteristics with the semiconductor layer (active layer), and will later constitute a part of the gate insulating film. In this way, the state shown in FIG.

Thereafter, a silicon oxynitride film 106 constituting a gate insulating film was formed to a thickness of 1000 angstroms. As a film forming method, for example, a plasma CVD method using a mixed gas of silane and N ₂ O or a plasma CVD method using a mixed gas of TEOS and N ₂ O is used. Here, silane and N ₂ O are used. The latter was used as a mixed gas. This silicon oxynitride film 106 functions as a gate insulating film together with the thermal oxide film 102.

  In addition, it is effective to include a halogen element in the silicon oxynitride film. That is, by fixing the nickel element by the action of the halogen element, the function of the gate insulating film as an insulating film due to the influence of the nickel element existing in the active layer (other metal elements that promote crystallization of silicon) Can be prevented from decreasing.

  Such a silicon oxynitride film has a significance that it is difficult for a metal element to enter the gate insulating film because of its dense film quality. When a metal element enters the gate insulating film, the function as the insulating film is lowered, which causes instability and variations in characteristics of the thin film transistor. As the gate insulating film, a commonly used silicon oxide film can also be used.

  After forming the silicon oxynitride film 106 functioning as a gate insulating film, an aluminum film (not shown, which becomes a pattern 107 after patterning described later) functioning as a gate electrode later was formed by sputtering. This aluminum film contained 0.2% by weight of scandium. The reason why scandium is contained in the aluminum film is to suppress generation of hillocks and whiskers in the subsequent process. Here, hillocks and whiskers mean that abnormal heating of aluminum occurs when heating is performed, and needle-like or stab-like protrusions are formed.

  After forming the aluminum film, a dense anodic oxide film (not shown) was formed. This anodic oxide film was formed by using an ethylene glycol solution containing 3% by weight of tartaric acid as an electrolytic solution. That is, in this electrolytic solution, an anodic oxidation film having a dense film quality is formed on the surface of the aluminum film by performing anodization using the aluminum film as an anode and platinum as a cathode. The film thickness of the anodic oxide film having a dense film quality (not shown) is about 100 angstroms. This anodic oxide film has a role of improving adhesion with a resist mask to be formed later. The film thickness of the anodic oxide film can be controlled by adjusting the applied voltage during anodic oxidation.

  Next, a resist mask 108 was formed, and the aluminum film was patterned into a pattern indicated by reference numeral 107. In this way, the state shown in FIG. 29B was obtained. Here, anodic oxidation was performed again. Here, a 3 wt% oxalic acid aqueous solution was used as the electrolytic solution. In this electrolytic solution, a porous anodic oxide film denoted by reference numeral 110 is formed by performing anodization using the aluminum pattern 107 as an anode.

  In the above process, the anodic oxide film 110 is selectively formed on the side surface of the aluminum pattern because the resist mask 108 having high adhesion exists on the upper part. This anodic oxide film can be grown to a thickness of several μm. Here, the film thickness was set to 6000 angstroms. The growth distance can be controlled by the anodic oxidation time. Next, the resist mask 108 was removed.

  Further, a dense anodic oxide film was formed again. That is, the anodic oxidation using the ethylene glycol solution containing 3% by weight of tartaric acid as an electrolytic solution was performed again. As a result, an anodic oxide film having a dense film quality is formed as indicated by reference numeral 111 because the electrolytic solution enters (invades) into the porous anodic oxide film 110. The film thickness of the dense anodic oxide film 111 was 1000 angstroms. The film thickness was controlled by adjusting the applied voltage.

  Here, the exposed silicon oxynitride film 106 and thermal oxide film 102 were etched. Dry etching was used for this etching. Next, the porous anodic oxide film 110 was removed using a mixed acid obtained by mixing acetic acid, nitric acid and phosphoric acid. In this way, the state shown in FIG. 29D was obtained. Thereafter, impurity ions were implanted. Here, in order to fabricate an N-channel thin film transistor, P (phosphorus) ions were implanted by a plasma doping method.

  In this step, regions 113 and 117 to be heavily doped and regions 114 and 116 to be lightly doped are formed. This is because a part of the remaining silicon oxide film 112 functions as a semi-transmissive mask, and a part of the implanted ions is shielded there. Next, the region into which the impurity ions have been implanted is activated by irradiation with laser light or strong light. Here, laser light is used. Thus, the source region 113, the channel formation region 115, the drain region 117, and the low concentration impurity regions 114 and 116 are formed in a self-aligned manner.

  Here, what is indicated by reference numeral 116 is a region called an LDD (lightly doped drain) region. When the film thickness of the dense anodic oxide film 111 is increased to 2000 angstroms or more, an offset gate region can be formed outside the channel formation region 115 with the film thickness. In this embodiment, the offset gate region is formed, but since the size thereof is small, the contribution due to its existence is small, and the drawing becomes complicated, so it is not shown in the drawing.

  Next, a silicon oxide film, a silicon nitride film, or a stacked film thereof is formed as the interlayer insulating film 118. Here, a silicon nitride film is used. The interlayer insulating film may be formed by forming a layer made of a resin material on a silicon oxide film or a silicon nitride film. Next, contact holes were formed, and a source electrode 119 and a drain electrode 120 were formed. Thus, the thin film transistor shown in FIG. 29E was completed.

Example 23
This example 23 relates to a method of forming the gate insulating film 106 in the configuration shown in the example 22. When a quartz substrate or a glass substrate having high heat resistance is used as the substrate, a thermal oxidation method can be used as a method for forming the gate insulating film. The thermal oxidation method can make the film quality dense and is useful for obtaining a thin film transistor having stable characteristics. In other words, an oxide film formed by a thermal oxidation method is dense as an insulating film and can reduce the movable charges existing therein, and thus is one of the optimum gate insulating films.

In this embodiment, as a method for forming the thermal oxide film, heat treatment was performed in an oxidizing atmosphere at a temperature of 950 ° C. At this time, it is effective to mix HCl or the like in the oxidizing atmosphere. By doing in this way, the metal element which exists in an active layer can be fixed simultaneously with formation of a thermal oxide film. It is also effective to mix a N ₂ O gas in an oxidizing atmosphere to form a thermal oxide film containing a nitrogen component. Here, if the mixing ratio of N ₂ O gas is optimized, it is possible to obtain a silicon oxynitride film by a thermal oxidation method. In this embodiment, it is not necessary to form the thermal oxide film 102 in particular.

Example 24
This Example 24 is an example in which a thin film transistor is manufactured by a process different from the processes described in Examples 22-23. FIG. 30 shows a manufacturing process of this example. First, a crystalline silicon film was formed on a glass substrate by the process shown in Example 16 or Example 17. And the state shown to FIG. 30 (A) was obtained by patterning it.

  Next, plasma treatment was performed in a mixed reduced pressure atmosphere of oxygen and hydrogen. In the state shown in FIG. 30A, 122 is a glass substrate, 123 is a base film, and 124 is an active layer formed of a crystalline silicon film. A portion denoted by reference numeral 121 is a thermal oxide film formed again after removal of the thermal oxide film for gettering.

Next, a silicon oxynitride film 125 constituting a gate insulating film was formed to a thickness of 1000 angstroms. As a film forming method, a plasma CVD method using a mixed gas of oxygen, silane, and N ₂ O or a mixed gas of TEOS and N ₂ O is used. Here, the former is used. The silicon oxynitride film 125 forms a gate insulating film together with the thermal oxide film 121. Note that a silicon oxide film can be used instead of the silicon oxynitride film.

  Following the formation of the silicon oxynitride film 125 that functions as a gate insulating film, an aluminum film (not shown) that functions as a gate electrode later was formed by sputtering. This aluminum film contained 0.2% by weight of scandium. After forming the aluminum film, a dense anodic oxide film (not shown) was formed. This anodic oxide film was formed by using an ethylene glycol solution containing 3% by weight of tartaric acid as an electrolytic solution. That is, in this electrolytic solution, anodization is performed using an aluminum film as an anode and platinum as a cathode, whereby an anodized film having a dense film quality is formed on the surface of the aluminum film.

  The film thickness of the anodic oxide film having a dense film quality (not shown) is about 100 angstroms. This anodic oxide film has a role of improving adhesion with a resist mask to be formed later. The film thickness of the anodic oxide film can be controlled by the applied voltage during anodic oxidation. Next, a resist mask 126 was formed, and the aluminum film was patterned into a pattern indicated by 127.

  Here, anodic oxidation was performed again. Here, a 3 wt% oxalic acid aqueous solution was used as the electrolytic solution. In this electrolytic solution, a porous anodic oxide film denoted by reference numeral 128 is formed by performing anodic oxidation using the aluminum pattern 127 as an anode. In this step, the anodic oxide film 128 is selectively formed on the side surface of the aluminum pattern because the resist mask 126 having high adhesion exists on the upper portion.

  This anodic oxide film can be grown to a thickness of several μm. Here, the film thickness was set to 6000 angstroms. Note that the growth distance can be controlled by adjusting the anodic oxidation time. Next, after removing the resist mask 126, a dense anodic oxide film was formed again. That is, the anodic oxidation using the ethylene glycol solution containing 3% by weight of tartaric acid as an electrolytic solution was performed again. Then, an anodic oxide film having a dense film quality is formed as indicated by reference numeral 129 because the electrolytic solution enters (penetrates) into the porous anodic oxide film 128.

  Next, the first impurity ions were implanted. This step may be performed after removing the resist mask 126. By this impurity ion implantation, a source region 130 and a drain region 132 are formed. Note that impurity ions are not implanted into the region denoted by reference numeral 131. Next, the porous anodic oxide film 128 was removed using a mixed acid obtained by mixing acetic acid, nitric acid and phosphoric acid. In this way, the state shown in FIG.

  Thereafter, impurity ions were implanted again. This impurity ion was performed under light doping conditions rather than the initial impurity ion implantation conditions. In this step, lightly doped regions 133 and 134 are formed, and a region denoted by reference numeral 135 becomes a channel forming region. Next, the region into which the impurity ions were implanted was activated by irradiation with intense light using an infrared lamp. Note that laser light may be used instead of the strong light. Thus, the source region 130, the channel formation region 135, the drain region 132, and the low concentration impurity regions 133 and 134 were formed in a self-aligned manner.

  Here, what is indicated by reference numeral 134 is a region called an LDD (lightly doped drain) region. Next, a silicon oxide film, a silicon nitride film, or a stacked film thereof is formed as the interlayer insulating film 136. Here, a silicon nitride film is formed. The interlayer insulating film may be formed by forming a layer made of a resin material on a silicon oxide film or a silicon nitride film. Next, contact holes were formed, and a source electrode 137 and a drain electrode 138 were formed. Thus, the thin film transistor shown in FIG. 30E was completed.

Example 25
Example 25 is an example in which an N-channel thin film transistor and a P-channel thin film transistor are configured to be complementary. FIG. 31 shows a manufacturing process of the twenty-fifth embodiment. The configuration shown in this embodiment can be used for various thin film integrated circuits integrated on an insulating surface, for example. For example, it can be used for a peripheral drive circuit of an active matrix liquid crystal display device.

  First, as shown in FIG. 31A, a silicon oxide film or a silicon oxynitride film was formed as a base film 141 over a glass substrate 140. A silicon oxynitride film is preferably used, which is used here. Further, an amorphous silicon film (not shown) is formed by a plasma CVD method or a low pressure thermal CVD method. Here, the low pressure thermal CVD method is used. Further, this amorphous silicon film was transformed into a crystalline silicon film by the method shown in Example 16.

  Next, plasma treatment was performed in a mixed atmosphere of oxygen and hydrogen, and the obtained crystalline silicon film was patterned to obtain active layers 142 and 143. In this way, the state shown in FIG. Here, in order to suppress the influence of carriers moving on the side surface of the active layer, in the state shown in FIG. 31A, in a nitrogen atmosphere containing 3% by volume of HCl, the temperature is 650 ° C. for 10 hours. Heat treatment was performed.

  If the trap level due to the presence of the metal element is present on the side surface of the active layer, the OFF current characteristics are deteriorated. Therefore, it is necessary to reduce the density of the level on the side surface of the active layer by performing the above treatment. Useful. Further, a thermal oxide film 139 silicon oxynitride film 144 constituting a gate insulating film was formed. Here, when quartz is used as the substrate, it is desirable to form the gate insulating film only by the thermal oxide film using the above-described thermal oxidation method.

  Next, an aluminum film (not shown) for forming a gate electrode later was formed to a thickness of 4000 angstroms. In addition to the aluminum film, an anodizable metal (for example, tantalum) can be used. After forming the aluminum film, an extremely thin dense anodic oxide film was formed on the surface by the method described above. Next, a resist mask (not shown) was placed on the aluminum film, and the aluminum film was patterned. Then, anodization was performed using the obtained aluminum pattern as an anode, and porous anodic oxide films 147 and 148 were formed.

  The thickness of the porous anodic oxide film was 5000 angstroms. Further, anodic oxidation was performed again under the conditions for forming a dense anodic oxide film, and dense anodic oxide films 149 and 150 were formed. Here, the dense anodic oxide films 149 and 150 have a thickness of 800 angstroms. In this way, the state shown in FIG. Further, the exposed silicon oxide film 144 and thermal oxide film 139 were removed by dry etching to obtain the state shown in FIG.

  After obtaining the state shown in FIG. 31C, the porous anodic oxide films 147 and 148 were removed using a mixed acid obtained by mixing acetic acid, nitric acid and phosphoric acid. In this way, the state shown in FIG. Here, resist masks are alternately arranged so that P (phosphorus) ions are implanted into the left thin film transistor and B (boron) ions are implanted into the right thin film transistor. By this impurity ion implantation, a source region 153 and a drain region 156 having a high concentration N-type are formed in a self-aligned manner.

  In addition, a weak N-type region 154 doped with P ions at a low concentration is formed at the same time, and a channel formation region 155 is formed at the same time. The reason why the weak N-type region indicated by reference numeral 154 is formed is that the remaining gate insulating film 151 exists. That is, P ions that have passed through the gate insulating film 151 are partially shielded by the gate insulating film 151.

  Further, the source region 160 and the drain region 157 having strong P-type are formed in a self-aligned manner by the same principle and method. At the same time, a low concentration impurity region 159 is formed, and a channel formation region 158 is formed at the same time. If the dense anodic oxide films 149 and 150 are thick, for example, 2000 angstroms, the offset gate region can be formed in contact with the channel formation region with that thickness.

  In the present embodiment, since the dense anodic oxide films 149 and 150 are as thin as 1000 angstroms or less, their presence can be ignored. Next, laser light was irradiated to anneal the region into which impurity ions were implanted. Note that strong light can be used instead of laser light. Subsequently, as shown in FIG. 31E, a silicon nitride film 161 and a silicon oxide film 162 were formed as interlayer insulating films. Each film thickness was 1000 angstroms. Note that the silicon oxide film 162 is not necessarily formed.

  Here, the thin film transistor is covered with the silicon nitride film. Since the silicon nitride film is dense and has good interface characteristics, the reliability of the thin film transistor can be improved with such a structure. Further, an interlayer insulating film 163 made of a resin material was formed by using a spin coating method, and the thickness of the interlayer insulating film 163 here was 1 μm.

  Next, contact holes are formed, and a source electrode 164 and a drain electrode 165 of the left N-channel thin film transistor are formed. At the same time, a source electrode 166 and a drain electrode 165 of the right thin film transistor are formed, and FIG. The configuration shown was obtained. Here, the drain electrodes 165 are arranged in common. In this way, a thin film transistor circuit having a complementary CMOS structure can be formed.

  In the structure shown in this embodiment, a structure in which the thin film transistor is covered with a nitride film and further covered with a resin material can be obtained. With this configuration, it is possible to provide a highly durable material that is difficult for mobile ions and moisture to enter. Further, when a multilayer wiring is formed, it is possible to prevent a capacitance from being formed between the thin film transistor and the wiring.

Example 26
Example 26 is an example in which a region that can be regarded as a single crystal or substantially a single crystal is formed by further irradiating the crystalline silicon film obtained in Example 16 or Example 17 with laser light. is there.

  First, as shown in Example 16, a crystalline silicon film was obtained by utilizing the action of nickel element. Next, the crystallinity was further promoted by irradiating the film with laser light. As the laser beam here, a KrF excimer laser was used. At that time, a region that can be regarded as a single crystal or substantially a single crystal can be formed by using a heat treatment at a temperature of 450 ° C. or higher and further optimizing the irradiation condition of the laser beam.

The film that greatly promotes crystallization by such a method has an electron spin density measured by ESR of 3 × 10 ¹⁷ cm ⁻³ or less, and the nickel element concentration is 3 × as the lowest value measured by SIMS. It has 10 ¹⁷ cm ⁻³ or less and further has a region that can be regarded as a single crystal. In this region, there is substantially no grain boundary, and high electrical characteristics comparable to a single crystal silicon wafer can be obtained.

The region that can be regarded as a single crystal contains hydrogen at 5 atomic% or less to about 1 × 10 ¹⁵ cm ⁻³ . This value was clarified by measurement by SIMS (secondary ion analysis method). By manufacturing a thin film transistor using such a single crystal or a region that can be regarded as a single crystal, a semiconductor device comparable to a MOS transistor manufactured using a single crystal wafer can be obtained.

Example 27
Example 27 is an example in which nickel element was directly introduced into the surface of the base film in the step shown in Example 16. In this case, the nickel element is held in contact with the lower surface of the amorphous silicon film. In this example, nickel element was introduced by applying a nickel acetate aqueous solution after the formation of the base film, and the nickel element (the metal element) was first held in contact with the surface of the base film. Other steps were the same as in Example 16, and a thin film transistor similar to that shown in FIG. 27E was completed. As a method for introducing the nickel element, a sputtering method, a CVD method, and an adsorption method can be used in addition to a method using a solution.

Example 28
In Example 28, a crystalline silicon film is obtained on a glass substrate using nickel element. In this embodiment, first, a crystalline silicon film having high crystallinity is obtained by the action of nickel element, and then laser light irradiation is performed to increase the crystallinity of the film and to be locally concentrated. Nickel element was diffused in the film. That is, the nickel mass disappeared.

  Next, an oxide film containing a halogen element was formed on the crystalline silicon film by a thermal oxidation method. At this time, the nickel element remaining in the crystalline silicon film is gettered into the thermal oxide film by the action of oxygen and halogen elements. At the same time, since the nickel element is dispersed by the previous laser beam irradiation, gettering proceeds effectively. Next, as a result of gettering, the thermal oxide film containing nickel element at a high concentration was removed. By doing so, a crystalline silicon film having a low nickel element concentration can be obtained while having high crystallinity on the glass substrate.

FIG. 32 is a diagram showing a manufacturing process of this example. First, a silicon oxynitride film 168 as a base film was formed on a Corning 1737 glass substrate (strain point 667 ° C.) 167 to a thickness of 3000 Å. The silicon oxynitride film was formed by a plasma CVD method using a mixed gas of silane, N ₂ O gas, and oxygen as a source gas. As the source gas, a mixed gas of TEOS gas and N ₂ O gas may be used.

  The silicon oxynitride film has a function of suppressing diffusion of impurities from a glass substrate (a large amount of impurities are included in the glass substrate as viewed from the semiconductor manufacturing level) in a later step. . In order to obtain the maximum function of suppressing the diffusion of impurities, a silicon nitride film is optimal. However, the silicon nitride film is not practical because it peels from the glass substrate due to stress. Note that a silicon oxide film can also be used as the base film.

  Further, it is important that the base film 168 has as high a hardness as possible. This is concluded from the fact that in the durability test of the finally obtained thin film transistor, the harder the base film is harder (that is, the lower the etching rate), the higher the reliability. Note that the reason is considered to be due to the shielding effect of impurities from the glass substrate during the manufacturing process of the thin film transistor.

  In addition, it is effective that the base film 168 contains a trace amount of a halogen element typified by chlorine. In this manner, a metal element that promotes crystallization of silicon present in the semiconductor layer can be gettered with a halogen element in a later step. It is also effective to add a hydrogen plasma treatment after forming the base film. In addition, it is effective to perform plasma treatment in an atmosphere in which oxygen and hydrogen are mixed. This is effective in removing the carbon component adsorbed on the surface of the base film and improving the interface characteristics with the semiconductor film to be formed later.

Next, an amorphous silicon film 169, which later becomes a crystalline silicon film, was formed to a thickness of 500 angstrom by a low pressure thermal CVD method. The reason why the low pressure thermal CVD method is used is that the film quality of the crystalline silicon film obtained later is superior, and specifically, the film quality is dense. As a method other than the low pressure thermal CVD method, a plasma CVD method or the like can be used. The amorphous silicon film produced here preferably has an oxygen concentration in the film of 5 × 10 ¹⁷ cm ⁻³ to 2 × 10 ¹⁹ cm ⁻³ . This is because oxygen plays an important role in the subsequent gettering step of a metal element (metal element that promotes crystallization of silicon). However, it should be noted that when the oxygen concentration is higher than the above concentration range, crystallization of the amorphous silicon film is inhibited.

Also, other impurity concentrations, such as nitrogen and carbon impurity concentrations, should be as low as possible. Specifically, the concentration needs to be 2 × 10 ¹⁹ cm ⁻³ or less. The upper limit of the thickness of the amorphous silicon film is about 2000 angstroms. This is because it is disadvantageous that the film is too thick in order to obtain the effect of the subsequent laser light irradiation. The disadvantage of the thick film is that most of the laser light applied to the silicon film is absorbed on the surface of the film. Note that the lower limit of the film thickness of the amorphous silicon film 169 is practically about 200 Å although it depends on the film forming method.

  Next, nickel element was introduced to crystallize the amorphous silicon film 169. Here, nickel element was introduced by applying an aqueous solution of nickel acetate containing nickel of 10 ppm (weight conversion) on the surface of the amorphous silicon film 169. As a method for introducing nickel element, in addition to the method using the above solution, sputtering method, CVD method, plasma treatment or adsorption method can be used.

  Among them, the method using the above solution is useful in that it is simple and the concentration of the metal element can be easily adjusted. By applying the nickel acetate aqueous solution, a water film of the nickel acetate solution is formed as indicated by reference numeral 170 in FIG. After obtaining this state, excess solution was blown off using a spinner (not shown). In this way, the nickel element was held in contact with the surface of the amorphous silicon film 169.

  In view of residual impurities in the subsequent heating step, for example, nickel sulfate is preferably used instead of using the nickel acetate aqueous solution. This is because the nickel acetate aqueous solution contains carbon, which is feared to carbonize and remain in the film in the subsequent heating step. The amount of nickel element introduced can be adjusted by adjusting the concentration of nickel salt in the solution.

  Next, in the state shown in FIG. 32B, heat treatment is performed at a temperature of 550 ° C. to 650 ° C. to crystallize the amorphous silicon film 169 to form a crystalline silicon film 171. It is preferable to perform the process temperature at the temperature below the strain point of a glass substrate. Since the strain point of the Corning 1737 glass substrate used here is 667 ° C., the upper limit is preferably set to about 650 ° C. with a margin. This heat treatment is performed in a reducing atmosphere. In this example, the heat treatment atmosphere was a nitrogen atmosphere containing 3% by volume of hydrogen, the heating temperature was 620 ° C., and the heating time was 4 hours.

The reason why the atmosphere is reduced in the crystallization process by the heat treatment is to prevent oxides from being formed during the heat treatment process. Specifically, this is to prevent nickel and oxygen from reacting to form NiO _x on the film surface or in the film. Oxygen is combined with nickel in a later gettering step and contributes greatly to the gettering of nickel.

  However, it has been found that the combination of oxygen and nickel at this crystallization stage inhibits crystallization. Therefore, in the crystallization process by heating, it is important to suppress the formation of oxide as much as possible. For this reason, the oxygen concentration in the atmosphere in which the heat treatment for crystallization is performed needs to be on the order of ppm, preferably 1 ppm or less.

  In addition to nitrogen, an inert gas such as argon or a mixed gas thereof can be used as a gas that occupies most of the atmosphere in which the heat treatment for crystallization is performed. After the crystallization step by the heat treatment, nickel element remains in a certain amount of mass. This was confirmed by observation with a TEM (transmission electron microscope). The cause for the fact that nickel is present in a certain amount of mass is not clear, but is believed to be related to some crystallization mechanism.

  Next, laser light irradiation is performed as shown in FIG. Here, a method of using a KrF excimer laser (wavelength 248 nm) and irradiating while scanning a linear laser beam shape was adopted. By this laser light irradiation, nickel elements that have been locally concentrated as a result of the crystallization by the heat treatment described above are dispersed in the film 171 to some extent. In other words, the mass of nickel element can be eliminated by laser irradiation, and the nickel element can be dispersed.

  Next, heat treatment was performed again in the process illustrated in FIG. This heat treatment is performed to form a thermal oxide film for gettering the nickel element. Here, the heat treatment was performed in an atmosphere containing a halogen element. Specifically, heat treatment was performed in an oxygen atmosphere containing 5% by volume of HCl. This step is for removing nickel element intentionally mixed in the initial stage for crystallization (the same applies to other metal elements that promote crystallization of silicon) from the crystalline silicon film 171. It is a process.

  The heat treatment is performed at a temperature higher than the heat treatment performed for performing the above-described crystallization. This is an important condition for effectively performing gettering of nickel element. Note that although it can be performed at a temperature equal to or lower than the heat treatment temperature performed for crystallization, the effect is small.

  This heat treatment is performed at a temperature of 600 ° C. to 750 ° C. after satisfying the above conditions. The nickel element gettering effect in this step can be remarkably obtained when the temperature is higher than 600 ° C., but in this embodiment, the gettering effect was performed at a temperature of 650 ° C. In this step, the nickel element dispersed by the laser beam irradiation is effectively gettered into the oxide film. Moreover, the upper limit of this heat processing temperature is restrict | limited by the strain point of the glass substrate to be used. Note that if the heat treatment is performed at a temperature equal to or higher than the strain point of the glass substrate to be used, care must be taken because the substrate is deformed.

  HCl is preferably mixed at a ratio of 0.5 to 10% by volume with respect to oxygen. It should be noted that when HCl is mixed at a concentration higher than this, the surface of the film is roughened to the same degree of unevenness as the film thickness. When heat treatment is performed under such conditions, a thermal oxide film 172 containing chlorine is formed as shown in FIG. In this embodiment, the heat treatment time is 12 hours, and the thickness of the thermal oxide film 172 is 100 angstroms.

  By forming the thermal oxide film 172, the thickness of the crystalline silicon film 169 becomes about 450 angstroms. In this heat treatment, when the heating temperature is 600 ° C. to 750 ° C., the treatment time (heating time) is 10 hours to 48 hours, typically 24 hours. Of course, this processing time may be set as appropriate depending on the thickness of the oxide film to be obtained. In this step, nickel element is gettered out of the silicon film by the action of oxygen and the action of halogen element. Here, nickel element is gettered in the thermal oxide film 172 formed by the action of chlorine.

  Oxygen is also involved in the gettering. In this gettering, oxygen present in the crystalline silicon film plays an important role. That is, gettering effect by chlorine acts on nickel oxide formed by combining oxygen and nickel, and gettering of nickel element effectively proceeds. As described above, when the concentration of oxygen is excessive, it becomes an element that inhibits crystallization of the amorphous silicon film 169 in the crystallization step shown in FIG. However, as described above, its presence plays an important role in the nickel gettering process. Therefore, it is important to control the concentration of oxygen present in the amorphous silicon film as the starting film.

In this embodiment, Cl is selected as the halogen element, and HCl is used as the introduction method. As the gas other than HCl, one or plural kinds of gases selected from HF, HBr, Cl ₂ , F ₂ , and Br ₂ can be used. In general, a hydride of halogen can be used. These gases, the content in the atmosphere (volume) to as long as HF 0.25 to 5%, if HBr 1 to 15%, if the Cl ₂ 0.25 to 5%, by F ₂ If it is 0.125 to 2.5%, Br ₂ is preferably 0.5 to 10%.

  If the concentration is lower than the above range, a significant effect cannot be obtained. Conversely, if the concentration is higher than the above range, the surface of the silicon film is roughened. Through this step, the nickel element concentration can be reduced to 1/10 or less of the initial concentration. This means that the nickel element can be reduced to 1/10 or less as compared with the case where no gettering with a halogen element is performed. This effect can be similarly obtained even when other metal elements are used. In the above process, since nickel element is gettered in the oxide film to be formed, the nickel concentration in the oxide film is naturally higher than in other regions.

  Further, a tendency for the nickel element to increase near the interface between the crystalline silicon film 171 and the thermal oxide film 172 is observed. It is considered that this is because the region where gettering is mainly performed is on the oxide film side in the vicinity of the interface between the crystalline silicon film and the oxide film. Moreover, it is considered that the gettering progresses in the vicinity of the interface between the two due to the presence of stress and defects in the vicinity of the interface.

  Next, the oxide film 172 containing nickel at a high concentration was removed. The removal of the oxide film 172 is performed by wet etching using buffered hydrofluoric acid (other hydrofluoric acid-based etchants) or dry etching. In this embodiment, wet etching using buffered hydrofluoric acid was performed.

  Thus, as shown in FIG. 32E, a crystalline silicon film 173 with a reduced concentration of nickel contained was obtained. Further, since the nickel element is relatively contained in the vicinity of the surface of the obtained crystalline silicon film 173, the etching of the oxide film 172 is further advanced, and the surface of the crystalline silicon film 173 is slightly over-etched. It is effective to do.

  It is effective to further promote the crystallinity of the obtained crystalline silicon film 173 by irradiating the laser beam again after removing the thermal oxide film 172. That is, it is effective to perform laser beam irradiation again after gettering of the nickel element. In this embodiment, an example is shown in which a KrF excimer laser (wavelength 248 nm) is used as the laser light to be used. However, a XeCl excimer laser (wavelength 308 nm) or other types of lasers can also be used. Moreover, it is good also as a structure which irradiates with an ultraviolet-ray and infrared rays instead of a laser beam.

Example 29
Example 29 is an example in which Cu is used as the metal element for promoting crystallization of silicon in the configuration shown in Example 28. In this case, cupric acetate [Cu (CH ₃ COO) ₂ ], cupric chloride (CuCl ₂ 2H ₂ O), or the like may be used as a solution for introducing Cu. Using dicopper (CuCl ₂ 2H ₂ O), the other steps were performed in the same manner as in Example 28 to obtain the state shown in FIG.

Example 30
Example 30 is an example in which crystal growth of a form different from Example 28 is performed. This embodiment relates to a method of performing crystal growth in a direction parallel to the substrate, called lateral growth, using a metal element that promotes crystallization of silicon. FIG. 33 is a diagram showing a manufacturing process of this example.

  First, a silicon oxynitride film having a thickness of 3000 angstroms was formed as a base film 175 on a Corning 1737 glass substrate 174. Note that a quartz substrate may be used instead of the glass substrate. Next, an amorphous silicon film 176 serving as a starting film for the crystalline silicon film was formed to a thickness of 600 angstroms by low pressure thermal CVD. As described above, the thickness of the amorphous silicon film is preferably 2000 angstroms or less. A plasma CVD method may be used instead of the low pressure thermal CVD method.

  Next, a silicon oxide film (not shown) was formed to a thickness of 1500 angstroms and patterned to form a mask indicated by reference numeral 177. This mask has an opening formed in a region indicated by 178. In the region where the opening 178 is formed, the amorphous silicon film 176 is exposed. The opening 178 has a long and narrow rectangle in the front direction (longitudinal direction) from the depth of the drawing. The width of the opening 178 is suitably 20 μm or more, and the length in the longitudinal direction may be a required length. In this embodiment, the width is 30 μm and the length is 4 cm.

  Next, in the same manner as shown in Example 28, a nickel acetate aqueous solution containing 10 ppm of nickel element in terms of weight was applied, and spin drying was performed using a spinner (not shown) to remove excess solution. In this manner, a state where the nickel element was held in contact with the exposed surface of the amorphous silicon film 176 was realized as indicated by a dotted line 179 in FIG.

  Next, heat treatment was performed at a temperature of 640 ° C. for 4 hours in a nitrogen atmosphere containing 3% by volume of hydrogen and containing as little oxygen as possible. Then, crystal growth progressed in a direction parallel to the substrate 174 as indicated by 180 in FIG. This crystal growth proceeds from the region of the opening 178 into which nickel element is introduced toward the periphery. This crystal growth in a direction parallel to the substrate is referred to as lateral growth or lateral growth in this specification.

  Under the conditions as shown in Example 30, this lateral growth can be performed over 100 μm or more. Thus, a crystalline silicon film 181 having a laterally grown region was obtained. In the region where the opening 178 is formed, crystal growth in the vertical direction called vertical growth proceeds from the surface of the silicon film toward the base interface.

  Next, the mask 177 made of a silicon oxide film for selectively introducing nickel element was removed to obtain the state shown in FIG. In this state, the silicon film 181 includes a vertical growth region, a lateral growth region, and a region where the crystal growth does not reach (amorphous state). In this state, nickel element is present in the film. It is unevenly distributed. In particular, the nickel element is present at a relatively high concentration in the region where the opening 178 was formed and the tip portion in the crystal growth direction indicated by reference numeral 180.

  Next, laser light irradiation is performed. Here, irradiation with KrF excimer laser was performed in the same manner as in Example 28. The nickel element unevenly distributed in this step is diffused, and a state in which gettering can be easily performed in the subsequent gettering step is obtained. After the completion of the laser light irradiation, heat treatment at a temperature of 650 ° C. was performed for 12 hours in an oxygen atmosphere containing 3% by volume of HCl. In this step, an oxide film 182 containing nickel element at a high concentration is formed, and at the same time, the nickel element concentration in the silicon film 181 is relatively reduced.

  Here, a thermal oxide film indicated by 182 was formed to a thickness of 100 angstroms. This thermal oxide film contains a high concentration of nickel element gettered by the action of oxygen and the action of chlorine, particularly the action of chlorine. Further, since the thermal oxide film 182 is formed, the crystalline silicon film 181 has a thickness of about 500 angstroms. Next, the thermal oxide film 182 containing nickel element at a high concentration was removed.

  The crystalline silicon film in this state has a concentration distribution such that nickel element exists at a high concentration toward the surface of the crystalline silicon film. This state is attributed to nickel element gettering in the thermal oxide film when the thermal oxide film 182 is formed. Therefore, after removing the thermal oxide film 182, it is useful to further etch the surface of the crystalline silicon film to remove the region where the nickel element is present at a high concentration. That is, by etching the surface of the crystalline silicon film in which nickel element is present at a high concentration, a crystalline silicon film having a further reduced nickel element concentration can be obtained. However, in this case, it is necessary to consider the film thickness of the finally obtained silicon film.

Next, patterning was performed to form a pattern 183 composed of a laterally grown region. The concentration of the nickel element remaining in the pattern 183 composed of the laterally grown regions thus obtained can be made lower than that shown in Example 28. This is also due to the fact that the concentration of the metal element contained in the lateral growth region is low in the first place. Specifically, the concentration of nickel element in the pattern 183 formed of the lateral growth region can be easily set to an order of 10 ¹⁷ cm ⁻³ or less.

  Further, when the thin film transistor is formed by using the lateral growth region, it is higher than that in the case of using the vertical growth region as shown in Example 28 (in the case of Example 28, the entire surface grows vertically). A semiconductor device having mobility can be obtained. Note that it is useful to remove the nickel element existing on the pattern surface by further performing an etching process after forming the pattern shown in FIG.

  Next, a thermal oxide film 184 was formed on the pattern 183. The thermal oxide film was formed to a thickness of 200 angstroms by performing a heat treatment in an oxygen atmosphere at a temperature of 650 ° C. for 12 hours. This thermal oxide film becomes a part of the gate insulating film later when a thin film transistor is formed. Thereafter, if a thin film transistor is to be manufactured, a silicon oxide film is formed by plasma CVD or the like to cover the thermal oxide film 184, and a gate insulating film is formed.

Example 31
Example 31 is an example in which a thin film transistor disposed in a pixel region of an active matrix liquid crystal display device or an active matrix EL display device is manufactured. FIG. 34 shows a manufacturing process of this example. First, in this example, a crystalline silicon film was formed on a glass substrate by the steps shown in Example 28 and Example 30, respectively.

  In the following description, the description will focus on the case of the process shown in Example 28, but the same applies to the case of the process shown in Example 30. After obtaining a crystalline silicon film with the structure shown in Example 28, it was patterned to obtain the state shown in FIG. In the state shown in FIG. 34A, reference numeral 186 is a glass substrate, 187 is a base film, and 188 is an active layer formed of a crystalline silicon film. After obtaining the state shown in FIG. 34A, plasma treatment was performed in a reduced-pressure atmosphere in which oxygen and hydrogen were mixed. This plasma was generated by high frequency discharge.

  By the plasma treatment, organic substances present on the exposed surface of the active layer 188 are removed. Precisely, the organic substance adsorbed on the surface of the active layer is oxidized by the oxygen plasma, and the oxidized organic substance is reduced and vaporized by the hydrogen plasma. In this way, organic substances present on the exposed surface of the active layer 188 are removed. This removal of organic matter is very effective in suppressing the presence of fixed charges on the surface of the active layer 188. Fixed charges resulting from the presence of organic substances hinder the operation of the device and cause instability of characteristics, and it is very useful to reduce the presence thereof.

After removing the organic matter, thermal oxidation was performed in an oxygen atmosphere at a temperature of 640 ° C. to form a 100 Å thermal oxide film 185. This thermal oxide film has high interface characteristics with the semiconductor layer, and will later constitute a part of the gate insulating film. Thus, the state shown in FIG. Thereafter, a silicon oxynitride film 189 constituting a gate insulating film was formed to a thickness of 1000 angstroms. As a film forming method, a plasma CVD method using a mixed gas of oxygen, silane, and N ₂ O was used. Note that a plasma CVD method using a mixed gas of TEOS and N ₂ O can also be used.

  This silicon oxynitride film 189 functions as a gate insulating film together with the thermal oxide film 185. In addition, it is effective to include a halogen element in the silicon oxynitride film. That is, by fixing the nickel element by the action of the halogen element, the gate insulating film is affected by the nickel element existing in the active layer (the same applies when other metal elements that promote crystallization of silicon are used). It is possible to prevent the function as an insulating film from deteriorating.

  The use of the silicon oxynitride film as described above has the significance that it is difficult for the metal element to enter the gate insulating film due to its dense film quality. When a metal element enters the gate insulating film, the function as the insulating film is lowered, which causes instability and variations in characteristics of the thin film transistor. Note that a commonly used silicon oxide film can also be used as the gate insulating film.

  After forming a silicon oxynitride film 189 that functions as a gate insulating film, an aluminum film (not shown) that functions as a gate electrode later was formed by sputtering. This aluminum film contained 0.2% by weight of scandium. The reason why scandium is contained in the aluminum film is to suppress generation of hillocks and whiskers in the subsequent process. Here, hillocks and whiskers mean that abnormal heating of aluminum occurs when heating is performed, and needle-like or stab-like protrusions are formed.

  After the aluminum film was formed, a dense anodic oxide film (not shown) was formed. This anodic oxide film was formed by using an ethylene glycol solution containing 3% by weight of tartaric acid as an electrolytic solution. That is, in this electrolytic solution, an anodic oxidation film having a dense film quality is formed on the surface of the aluminum film by performing anodization using the aluminum film as an anode and platinum as a cathode. The film thickness of the anodic oxide film having a dense film quality (not shown) is about 100 angstroms. This anodic oxide film has a role of improving adhesion with a resist mask to be formed later. The film thickness of the anodic oxide film can be controlled by the applied voltage during anodic oxidation.

  Next, a resist mask 191 was formed. Then, the aluminum film was patterned into a pattern indicated by reference numeral 190, thus obtaining the state shown in FIG. Here, anodic oxidation was performed again. Here, a 3 wt% oxalic acid aqueous solution was used as the electrolytic solution. In this electrolytic solution, a porous anodic oxide film indicated by reference numeral 193 is formed by performing anodization using the aluminum pattern 190 as an anode.

  In the above process, the anodic oxide film 193 is selectively formed on the side surface of the aluminum pattern because the resist mask 191 having high adhesion exists on the upper part. The anodic oxide film 193 can be grown to a thickness of several μm, but here the thickness is set to 6000 Å. The growth distance can be controlled by the anodic oxidation time.

  Next, after removing the resist mask 191, a dense anodic oxide film was formed again. That is, the anodic oxidation using the ethylene glycol solution containing 3% by weight of tartaric acid as an electrolytic solution was performed again. As a result, an anodic oxide film having a dense film quality is formed as indicated by reference numeral 194 because the electrolytic solution enters (invades) into the porous anodic oxide film 193. The film thickness of this dense anodic oxide film 194 was 1000 angstroms. This film thickness was controlled by the applied voltage.

  Next, the exposed silicon oxynitride film 189 and thermal oxide film 185 were etched. Dry etching was used for this etching. Further, the porous anodic oxide film 193 was removed using a mixed acid obtained by mixing acetic acid, nitric acid and phosphoric acid. In this way, the state shown in FIG. Thereafter, impurity ions were implanted.

  Here, in order to fabricate an N-channel thin film transistor, P (phosphorus) ions are implanted by a plasma doping method. In this step, regions 196 and 200 that are heavily doped and regions 197 and 199 that are lightly doped are formed. This is because part of the remaining silicon oxide film 195 functions as a semi-transmissive mask and part of the implanted ions is shielded there.

  Next, the region into which the impurity ions were implanted was activated by irradiation with laser light or strong light. Here, it was carried out by irradiation with strong light from an ultraviolet lamp. Thus, the source region 196, the channel formation region 198, the drain region 200, and the low-concentration impurity regions 197 and 199 are formed in a self-aligned manner. Here, what is indicated by reference numeral 199 is a region called an LDD (lightly doped drain) region.

  When the film thickness of the dense anodic oxide film 194 is increased to 2000 angstroms or more, an offset gate region can be formed outside the channel formation region 198 with the film thickness. The off-gate region is also formed in this embodiment, but since its size is small, the contribution due to its existence is small, and the drawing becomes complicated, so it is not shown in the drawing.

  Next, a silicon oxide film, a silicon nitride film, or a stacked film thereof is formed as the interlayer insulating film 201. Here, a silicon nitride film was used. The interlayer insulating film may be formed by forming a layer made of a resin material on a silicon oxide film or a silicon nitride film. Further, contact holes were formed, and a source electrode 202 and a drain electrode 203 were formed. Thus, the thin film transistor shown in FIG. 34E was completed.

<< Example 32 >>
The present embodiment 32 is an example relating to a method of forming the gate insulating film 189 in the configuration shown in the actual example 31 (FIG. 34). When a quartz substrate or a glass substrate having high heat resistance is used as the substrate, a thermal oxidation method can be used as a method for forming the gate insulating film. The thermal oxidation method can make the film quality dense and is useful for obtaining a thin film transistor having stable characteristics.

  That is, an oxide film formed by a thermal oxidation method is dense as an insulating film and can reduce the movable charges existing therein, so that it becomes one of the optimum gate insulating films. In this example, heat treatment was performed in an oxidizing atmosphere at a temperature of 950 ° C. The other steps were the same as in Example 31 to complete the thin film transistor as shown in FIG. At this time, it is effective to mix HCl or the like in an oxidizing atmosphere.

By doing in this way, the metal element which exists in an active layer can be fixed simultaneously with formation of a thermal oxide film. It is also effective to form a thermal oxide film containing a nitrogen component by mixing N ₂ O gas in an oxidizing atmosphere. Here, if the mixing ratio of N ₂ O gas is optimized, it is possible to obtain a silicon oxynitride film by a thermal oxidation method. In this embodiment, it is not necessary to form the thermal oxide film 185 in particular.

Example 33
Example 33 is an example in which a thin film transistor was manufactured by a process different from the process of Example 31 (FIG. 34). FIG. 35 shows a manufacturing process of this example. First, crystalline silicon films were formed on a glass substrate by the steps shown in Example 28 and Example 30, respectively. Subsequently, the state shown in FIG. 35A was obtained by patterning them. In the following description, the description will focus on the case of the process shown in Example 30, but the same applies to the case of the process shown in Example 28.

After obtaining the state shown in FIG. 35A, plasma treatment was performed in a mixed reduced pressure atmosphere of oxygen and hydrogen. In the state shown in FIG. 35A, 205 is a glass substrate, 206 is a base film, and 207 is an active layer formed of a crystalline silicon film. Reference numeral 204 denotes a thermal oxide film formed again after removing the thermal oxide film for gettering. Thereafter, a silicon oxynitride film 208 constituting a gate insulating film was formed to a thickness of 1000 angstroms. This film formation was performed by a plasma CVD method using a mixed gas of oxygen, silane, and N ₂ O. As a film formation method, a plasma CVD method using a mixed gas of TEOS and N ₂ O may be used.

  The silicon oxynitride film 208 and the thermal oxide film 204 constitute a gate insulating film. Note that a silicon oxide film can be used instead of the silicon oxynitride film. After forming a silicon oxynitride film 208 that functions as a gate insulating film, an aluminum film (not shown) that functions as a gate electrode later is formed by sputtering. This aluminum film contained 0.2% by weight of scandium.

  Next, a dense anodic oxide film (not shown) was formed. This anodic oxide film was formed by using an ethylene glycol solution containing 3% by weight of tartaric acid as an electrolytic solution. That is, in this electrolytic solution, an anodic oxidation film having a dense film quality is formed on the surface of the aluminum film by performing anodization using the aluminum film as an anode and platinum as a cathode. The film thickness of the anodic oxide film having a dense film quality (not shown) is about 100 angstroms. This anodic oxide film has a role of improving adhesion with a resist mask to be formed later. The film thickness of the anodic oxide film can be controlled by the applied voltage during anodic oxidation.

  Next, a resist mask 209 was formed. The aluminum film was patterned into a pattern indicated by reference numeral 210. Here, anodic oxidation is performed again. Here, a 3 wt% oxalic acid aqueous solution was used as the electrolytic solution. In this electrolytic solution, a porous anodic oxide film denoted by reference numeral 211 is formed by performing anodization using the aluminum pattern 210 as an anode.

  In this step, the anodic oxide film 211 is selectively formed on the side surface of the aluminum pattern because the resist mask 209 having high adhesion exists on the upper portion. The anodic oxide film 211 can be grown to a thickness of several μm, but here the thickness is set to 6000 angstroms. The growth distance can be controlled by the anodic oxidation time.

  Next, after removing the resist mask 209, a dense anodic oxide film was formed again. That is, the anodic oxidation using the ethylene glycol solution containing 3% by weight of tartaric acid as an electrolytic solution was performed again. As a result, an anodic oxide film having a dense film quality is formed as indicated by reference numeral 212 because the electrolytic solution enters (invades) into the porous anodic oxide film 211. Although the first impurity ion implantation is performed here, this step may be performed after the resist mask 209 is removed. A source region 213 and a drain region 215 were formed by this impurity ion implantation. Note that impurity ions are not implanted into the region denoted by reference numeral 214.

  Next, the porous anodic oxide film 211 was removed using a mixed acid obtained by mixing acetic acid, nitric acid and phosphoric acid. In this way, the state shown in FIG. Thereafter, impurity ions were implanted again. This impurity ion was performed under the condition of light doping rather than the initial impurity ion implantation condition. In this step, lightly doped regions 216 and 217 are formed. A region indicated by reference numeral 218 becomes a channel formation region.

  Next, the region into which the impurity ions have been implanted is activated by irradiating with laser light or strong light. Here, laser light is used. Thus, the source region 213, the channel formation region 218, the drain region 215, and the low concentration impurity regions 216 and 217 were formed in a self-aligned manner. Here, what is indicated by reference numeral 217 is a region called an LDD (lightly doped drain) region.

  Next, a silicon oxide film, a silicon nitride film, or a stacked film thereof is formed as the interlayer insulating film 219. Here, a stacked film of a silicon oxide film and a silicon nitride film is formed. Note that the interlayer insulating film may be formed by forming a layer made of a resin material over a silicon oxide film or a silicon nitride film. Then, contact holes were formed, and a source electrode 220 and a drain electrode 221 were formed. Thus, the thin film transistor shown in FIG. 35E was completed.

<< Example 34 >>
The present embodiment 34 is an example in which an N-channel type thin film transistor and a P-channel type thin film transistor are configured to be complementary. The configuration shown in this embodiment can be used for various thin film integrated circuits integrated on an insulating surface, for example. For example, it can be used for a peripheral drive circuit of an active matrix liquid crystal display device. FIG. 36 shows a manufacturing process of this example.

  First, as illustrated in FIG. 36A, a silicon oxide film or a silicon oxynitride film is formed as a base film 224 over a glass substrate 223. Of these, a silicon oxynitride film is preferably used, but this is used here. Next, an amorphous silicon film (not shown) was formed by a plasma CVD method. In addition, you may form into a film by low pressure thermal CVD method. Further, this amorphous silicon film was transformed into a crystalline silicon film by the method shown in Example 28.

  Next, plasma treatment was performed in a mixed atmosphere of oxygen and hydrogen, and the obtained crystalline silicon film was patterned to obtain active layers 225 and 226. In this way, the state shown in FIG. Further, here, in order to suppress the influence of carriers moving on the side surface of the active layer, in the state shown in FIG. 36A, in a nitrogen atmosphere containing 3% by volume of HCl, the temperature is 650 ° C. for 10 hours. The heat treatment was performed.

  If the trap level due to the presence of the metal element is present on the side surface of the active layer, the OFF current characteristics are deteriorated. Therefore, it is necessary to reduce the density of the level on the side surface of the active layer by performing the above treatment. Useful. Further, a thermal oxide film 222 and a silicon oxynitride film 227 constituting a gate insulating film were formed. Here, when quartz is used as the substrate, it is desirable that the gate insulating film is constituted only by the thermal oxide film using the above-described thermal oxidation method.

  Next, an aluminum film (not shown) for forming a gate electrode later was formed to a thickness of 4000 angstroms. As the metal other than aluminum, an anodizable metal (for example, tantalum) can be used. After forming the aluminum film, an extremely thin dense anodic oxide film was formed on the surface by the method described above. Next, a resist mask (not shown) was placed on the aluminum film, and the aluminum film was patterned.

  Subsequently, anodization was performed using the aluminum pattern obtained above as an anode to form porous anodic oxide films 230 and 231. The thickness of the porous anodic oxide film was 5000 angstroms. Further, anodic oxidation was performed again under the conditions for forming dense anodic oxide films, and dense anodic oxide films 232 and 233 were formed. Here, the dense anodic oxide films 232 and 233 have a thickness of 800 angstroms. In this way, the state shown in FIG.

  Further, the exposed silicon oxide film 227 and the thermal oxide film 222 were removed by dry etching to obtain the state shown in FIG. Thereafter, the porous anodic oxide films 230 and 231 were removed using a mixed acid obtained by mixing acetic acid, nitric acid and phosphoric acid. In this way, the state shown in FIG. Here, resist masks are alternately arranged so that P (phosphorus) ions are implanted into the left thin film transistor and B (boron) ions are implanted into the right thin film transistor.

  By the implantation of the impurity ions, a source region 236 and a drain region 239 having a high concentration N type are formed in a self-aligned manner. At the same time, a weak N-type region 237 doped with P ions at a low concentration was formed, and a channel formation region 238 was simultaneously formed. The reason why the weak N-type region indicated by reference numeral 237 is formed is that the remaining gate insulating film 234 exists. That is, P ions that have passed through the gate insulating film 234 are partially shielded by the gate insulating film 234.

  The source region 243 and the drain region 240 having a strong P-type are formed in a self-aligned manner by the same principle and method as described above. At the same time, a low concentration impurity region 242 is formed at the same time, and a channel formation region 241 is formed at the same time. When the dense anodic oxide films 232 and 233 are as thick as 2000 angstroms, the offset gate region can be formed in contact with the channel formation region with that thickness.

  In the case of this embodiment, since the dense anodic oxide films 232 and 233 are as thin as 1000 angstroms or less, their presence can be ignored. Next, the region into which the impurity ions were implanted was annealed by laser light irradiation. In addition, it can replace with a laser beam and can also carry out by irradiation of a strong light. Next, as shown in FIG. 36E, a silicon nitride film 244 and a silicon oxide film 245 are formed as interlayer insulating films. Each film thickness was 1000 angstroms. Note that the silicon oxide film 245 is not necessarily formed.

  Here, the thin film transistor is covered with the silicon nitride film. Since the silicon nitride film is dense and has good interface characteristics, the reliability of the thin film transistor can be improved with such a structure. Further, an interlayer insulating film 246 made of a resin material is formed by using a spin coating method. Here, the thickness of the interlayer insulating film 246 is 1 μm.

  Then, contact holes were formed, and a source electrode 247 and a drain electrode 248 of the left N-channel thin film transistor were formed. At the same time, a source electrode 249 and a drain electrode 248 of the right thin film transistor were formed (the drain electrode 248 was disposed in common), and the thin film transistor shown in FIG. 36F was completed. In this way, a thin film transistor circuit having a complementary CMOS structure can be formed.

  In the structure shown in this embodiment 34, a structure in which the thin film transistor is covered with a nitride film and further covered with a resin material can be obtained. This configuration can be made highly durable such that mobile ions and moisture do not easily enter. Further, when a multilayer wiring is formed, it is possible to prevent a capacitance from being formed between the thin film transistor and the wiring.

Example 35
Example 35 is an example in which nickel element was directly introduced into the surface of the base film in the step shown in Example 28. In this case, the nickel element is held in contact with the lower surface of the amorphous silicon film. In this embodiment, after the base film is formed, nickel element is introduced, and the nickel element is first held in contact with the surface of the base film.

  In this example, nickel element was introduced by applying an aqueous solution of nickel acetate containing nickel of 10 ppm (weight conversion) to the surface of the base film, and an amorphous silicon film was formed on this surface. Other steps were performed in the same manner as in Example 28, and as shown in FIG. 32E, a crystalline silicon film 173 with a reduced nickel content was obtained. As a method for introducing a metal element that promotes crystallization of silicon, a sputtering method, a CVD method, a plasma treatment, and an adsorption method can be used in addition to the method using the above solution.

Example 36
In this Example 36, an island shape made of a crystalline silicon film obtained by irradiating laser light in the state of FIG. 33 (E), FIG. 34 (A), or FIG. 35 (A). This is an example in which the crystallinity of the pattern is improved. In this embodiment, a predetermined annealing effect can be obtained with a relatively low irradiation energy density by irradiating laser light in the states of FIGS. 33 (E), 34 (A), and 35 (A). I was able to. This effect is considered to be because energy efficiency used for annealing is increased because laser energy is irradiated to a small area.

Example 37
In this example 37, the patterning of the active layer of the thin film transistor was devised in order to enhance the annealing effect by laser light irradiation. FIG. 37 shows a manufacturing process of a thin film transistor in this example.

  First, a silicon oxide film or a silicon oxynitride film 251 was formed as a base film on a Corning 1737 glass substrate 250. Next, an amorphous silicon film was formed to a thickness of 500 angstroms. A low pressure thermal CVD method was used for this film formation. This amorphous silicon film becomes a crystalline silicon film 252 through the following crystallization process.

  Next, the amorphous silicon film was crystallized by the methods shown in Example 28 (see FIG. 32) and Example 29 (see FIG. 33), respectively, to obtain a crystalline silicon film. In this way, the state shown in FIG. Then, according to the process shown in Example 28 and Example 29, the crystalline silicon film 252 was formed on the glass substrate, respectively. That is, the amorphous silicon film was crystallized by heat treatment using nickel element, and a crystalline silicon film 252 was obtained. This treatment was performed by heat treatment at a temperature of 620 ° C. for 4 hours. The subsequent steps are the same for the crystalline silicon film formed by any of the steps of Example 28 and Example 29.

  After obtaining the crystalline silicon film, a pattern 253 for forming an active layer of the thin film transistor was formed. In this case, the cross-sectional shape of this pattern was a shape as indicated by 254 in FIG. The reason why the pattern 253 is formed in such a shape 254 is to prevent the shape of the pattern from being deformed in a subsequent process step by laser light irradiation.

  In general, when a laser beam is applied to a pattern 258 made of a normal island-shaped silicon film formed on a base 257 as shown in FIG. 38A, a laser beam as shown in FIG. The convex part 260 will be formed in the edge part of the pattern 259 after light irradiation. This is considered to occur because the energy of the irradiated laser beam is concentrated on the edge portion of the pattern where there is no heat escape.

  The above phenomenon becomes a cause of a defect in wiring that later constitutes the thin film transistor and a malfunction of the thin film transistor. Therefore, in the configuration shown in this example, the active layer pattern 253 has a cross-sectional shape as shown in FIG. With such a structure, the pattern of the silicon film can be prevented from having a shape as illustrated in FIG.

  Here, it is preferable that the angle of the portion indicated by reference numeral 254 is 20 ° to 50 ° with respect to the surface of the base film 251. It is not preferable to set the angle of the portion indicated by reference numeral 254 to be less than 20 ° because an increase in the area occupied by the active layer and difficulty in formation are increased. In addition, if the angle of the portion indicated by reference numeral 254 exceeds 50 °, the effect of suppressing the formation of the shape shown in FIG.

  A pattern as indicated by reference numeral 253 can be realized by utilizing isotropic dry etching at the time of patterning and controlling the dry etching conditions. Next, after obtaining a pattern having a shape indicated by 253 in FIG. 37B (which will later become an active layer), irradiation with laser light was performed as shown in FIG. In this step, the nickel element that is locally solidified in the pattern 253 can be diffused. Further, the crystallinity can be promoted.

  After the laser light irradiation, heat treatment was performed in an oxygen atmosphere containing 3% by volume of HCl to form a thermal oxide film 255. Here, a thermal oxide film of 100 angstroms was formed by performing a heat treatment for 12 hours in an oxygen atmosphere containing 3% by volume of HCl at a temperature of 650 ° C. This thermal oxide film is gettered with the nickel element contained in the pattern 253 by the action of chlorine. At this time, since the mass of the nickel element is destroyed and diffused by the laser beam irradiation in the previous step, gettering of the nickel element is effectively performed.

  Further, when the configuration shown in this embodiment is adopted, gettering from the side surface of the pattern 253 is also performed. This is useful in improving the OFF current characteristics and reliability of the finally completed thin film transistor. This is because the presence of a metal element that promotes crystallization of silicon represented by nickel element present on the side surface of the active layer is greatly related to an increase in OFF current and instability of characteristics.

  After the gettering thermal oxide film 255 shown in FIG. 37D was formed, the thermal oxide film 255 was removed. In this way, the state shown in FIG. Note that, when a silicon oxide film is employed as the base film 251, there is a concern that the silicon oxide film 251 is etched in the removal process of the thermal oxide film 255. However, when the thickness of the thermal oxide film 255 is as thin as about 100 Å as shown in this embodiment, this is not a big problem.

  After obtaining the state shown in FIG. 37E, a new thermal oxide film 256 was formed. This thermal oxide film was formed by heat treatment in an atmosphere of 100% oxygen. Here, the thermal oxide film 256 is formed to a thickness of 100 Å by heat treatment in the oxygen atmosphere at a temperature of 650 ° C. This thermal oxide film 256 is effective in suppressing the surface of the pattern 253 from becoming rough during subsequent laser light irradiation. The thermal oxide film 256 later constitutes a part of the gate insulating film.

  Since the thermal oxide film 256 has very good interface characteristics with the crystalline silicon film 253, it is useful to use it as a part of the gate insulating film. Note that after the thermal oxide film 256 is formed, laser light irradiation may be performed again. In this way, the concentration of nickel element was reduced, and a crystalline silicon film 253 having high crystallinity was obtained. Thereafter, a thin film transistor is manufactured through a process as shown in FIG.

Example 38
The present Example 38 is an example about the device in the case of applying heat treatment at a temperature equal to or higher than the strain point of the glass substrate. In the present invention, the metal element gettering step for promoting crystallization of silicon is preferably performed at a temperature as high as possible.

  For example, when a Corning 1737 glass substrate (strain point 667 ° C.) is used, the temperature at which nickel element is gettered by forming a thermal oxide film is higher at 650 ° C. than at 650 ° C. Obtainable. However, when the Corning 1737 glass substrate is used and the heating temperature for forming the thermal oxide film is set to 700 ° C., the glass substrate is deformed.

  The present embodiment is an example in which this problem is solved. In other words, in the configuration shown in this example, the glass substrate was placed on a surface plate made of quartz with guaranteed flatness, and heat treatment was performed in this state. In this way, the flatness of the softened glass substrate was also maintained by the flatness of the surface plate. In addition, it is important to perform cooling in a state where a glass substrate is placed on a surface plate. By adopting such a configuration, heat treatment can be performed even at a temperature equal to or higher than the strain point of the glass substrate.

Example 39
In Example 39, a crystalline silicon film was obtained on a glass substrate using nickel element. In this embodiment, first, a crystalline silicon film having high crystallinity is obtained by the action of nickel element, and then laser light irradiation is performed. By irradiating this laser light, the crystallinity of the film is enhanced and nickel elements present locally concentrated in the film are diffused in the film. That is, the nickel mass disappears.

  Then, an oxide film was formed on the crystalline silicon film by a thermal oxidation method. At this time, the nickel element remaining in the crystalline silicon film is gettered in the thermal oxide film. However, since the nickel element is dispersed by the irradiation of the laser beam, gettering proceeds effectively. To do. Next, as a result of the gettering, the thermal oxide film containing nickel element at a high concentration was removed. By doing so, a crystalline silicon film having high crystallinity on the glass substrate and having a low nickel element concentration was obtained.

FIG. 39 is a diagram showing a manufacturing process of this example. First, a silicon oxynitride film 262 as a base film was formed to a thickness of 3000 angstrom on a Corning 1737 glass substrate (strain point 667 ° C.) 261. The silicon oxynitride film was formed using a plasma CVD method using silane, N ₂ O gas, and oxygen as source gases. Instead of this, a plasma CVD method using TEOS gas and N ₂ O gas may be used.

  The silicon oxynitride film has a function of suppressing diffusion of impurities from a glass substrate (a large amount of impurities are included in the glass substrate as viewed from the semiconductor manufacturing level) in a later step. . In order to obtain the maximum function of suppressing the diffusion of impurities, a silicon nitride film is optimal. However, the silicon nitride film is not practical because it peels off the glass substrate due to stress. A silicon oxide film can also be used as the base film.

  In addition, it is important that the base film 262 have as high a hardness as possible. This is concluded in the durability test of the thin film transistor finally obtained because the harder the base film is harder (that is, the lower the etching rate), the higher the reliability. The reason is considered to be due to the shielding effect of impurities from the glass substrate during the manufacturing process of the thin film transistor.

  In addition, it is effective to add a trace amount of a halogen element typified by chlorine in the base film 262. In this manner, in a later step, a metal element that promotes crystallization of silicon existing in the semiconductor layer can be gettered with a halogen element. It is also effective to add a hydrogen plasma treatment after forming the base film. Furthermore, it is effective to perform plasma treatment in an atmosphere in which oxygen and hydrogen are mixed. This is effective in removing the carbon component adsorbed on the surface of the base film and improving the interface characteristics with the semiconductor film to be formed later.

  Next, an amorphous silicon film 263, which later becomes a crystalline silicon film, was formed to a thickness of 500 angstrom by low pressure thermal CVD. The reason why the low pressure thermal CVD method is used is that the crystalline silicon film obtained later is superior in film quality. Specifically, the film quality is dense. As a method other than the low pressure thermal CVD method, a plasma CVD method can be used.

The amorphous silicon film produced here preferably has an oxygen concentration in the film of 5 × 10 ¹⁷ cm ⁻³ to 2 × 10 ¹⁹ cm ⁻³ . This is because oxygen plays an important role in the subsequent gettering process of the metal element that promotes the crystallization of silicon. However, when the oxygen concentration is higher than the above concentration range, care must be taken because crystallization of the amorphous silicon film is inhibited. Further, other impurity concentrations, for example, nitrogen and carbon impurity concentrations are preferably as low as possible. Specifically, the concentration needs to be 2 × 10 ¹⁹ cm ⁻³ or less.

  The upper limit of the thickness of the amorphous silicon film 265 is about 2000 angstroms. This is because a film that is too thick is disadvantageous in order to obtain the effect of subsequent laser light irradiation. The disadvantage of the thick film is that most of the laser light applied to the silicon film is absorbed on the surface of the film. Note that the lower limit of the thickness of the amorphous silicon film 263 is practically about 200 Å, although it depends on the film forming method.

  Next, nickel element was introduced to crystallize the amorphous silicon film 263. Here, nickel element was introduced by applying a nickel acetate aqueous solution containing 10 ppm (weight conversion) of nickel to the surface of the amorphous silicon film 263. As a method for introducing nickel element, in addition to the method using the above solution, a sputtering method, a CVD method, a plasma treatment or an adsorption method can be used. Of these, the method using the above solution is useful in that it is simple and the concentration of the metal element can be easily adjusted.

  By applying the nickel acetate aqueous solution as described above, a water film of the nickel acetate aqueous solution was formed as indicated by 264 in FIG. Thereafter, excess solution was blown off using a spinner (not shown). Thus, the nickel element was held in contact with the surface of the amorphous silicon film 263. In view of residual impurities in the subsequent heating step, for example, nickel sulfate is preferably used instead of the nickel acetate salt solution. This is because the nickel acetate salt solution contains carbon, which is feared to carbonize and remain in the film in the subsequent heating step. The amount of nickel element introduced can be adjusted by adjusting the concentration of nickel element in the solution.

  Then, in the state shown in FIG. 39B, heat treatment is performed at a temperature of 550 ° C. to 650 ° C. to crystallize the amorphous silicon film 263, so that a crystalline silicon film 265 is obtained. This heat treatment was performed in a reducing atmosphere. The temperature of the heat treatment is preferably performed at a temperature below the strain point of the glass substrate. Since the strain point of the Corning 1737 glass substrate is 667 ° C., the upper limit of the heating temperature in this case is preferably about 650 ° C. with a margin.

In this example, the reducing atmosphere was a nitrogen atmosphere containing 3% by volume of hydrogen, the heating temperature was 620 ° C., and the heating time was 4 hours. In the crystallization process by the heat treatment, the atmosphere is reduced to prevent an oxide from being formed during the heat treatment process. More specifically, the reaction with nickel and oxygen, because the NiO _X is prevented from undesirably formed on the surface of the film or within the film.

  Note that oxygen is combined with nickel in a later gettering step and contributes greatly to the gettering of nickel. However, it has been found that the combination of oxygen and nickel in the crystallization stage inhibits crystallization. Therefore, in the crystallization process by heating, it is important to suppress the formation of oxide as much as possible.

  Therefore, the oxygen concentration in the atmosphere in which the heat treatment for crystallization is performed needs to be on the order of ppm, preferably 1 ppm or less. Moreover, as gas which occupies most of the atmosphere which performs the heat processing for said crystallization, inert gas, such as argon other than nitrogen, or those mixed gas can be utilized.

  After the crystallization step by the heat treatment, nickel element remains in a certain amount of mass. This was confirmed by observation with a TEM (transmission electron microscope). The cause of the fact that the nickel is present in a certain amount of mass is not clear, but is thought to be related to some crystallization mechanism.

  Next, laser light irradiation was performed as shown in FIG. Here, a method of using a KrF excimer laser (wavelength 248 nm) and irradiating while scanning a linear laser beam shape was adopted. By this laser light irradiation, nickel elements that have been locally concentrated in the film 265 are dispersed to some extent as a result of the crystallization by the heat treatment described above. That is, the mass of nickel element can be eliminated and the nickel element can be dispersed in the film 265.

  Next, heat treatment was performed again as illustrated in FIG. This heat treatment is performed to form a thermal oxide film for gettering the nickel element. Here, heat treatment at a temperature of 640 ° C. was performed in a 100% oxygen atmosphere for 12 hours. As a result of this step, a thermal oxide film was formed to a thickness of 100 Å.

  This step is a step for removing nickel element intentionally mixed in the initial stage for crystallization (the same applies to other metal elements that promote crystallization of silicon) from the crystalline silicon film 265. It is. This heat treatment is performed at a temperature higher than that of the heat treatment performed for the above-described crystallization, which is an important condition for effectively performing gettering of nickel element. Note that although it can be performed at a temperature equal to or lower than the heat treatment temperature performed for crystallization, the effect is small.

  This heat treatment is performed at a temperature of 600 ° C. to 750 ° C. after satisfying the above conditions. The gettering effect of nickel element in this step can be remarkably obtained when the temperature is higher than 600 ° C. In this step, the nickel element dispersed by the laser beam irradiation is effectively gettered into the oxide film. In addition, the upper limit of this heat processing temperature is restrict | limited by the strain point of the glass substrate to be used.

  When heat treatment is performed at a temperature equal to or higher than the strain point of the glass substrate to be used, care must be taken because the substrate is deformed. In this regard, as described in the section << Example 38 >>, the glass substrate is placed on a surface plate made of quartz, for example, which is guaranteed flatness, and heat treatment is performed in this state. Thus, heat treatment can be performed at a temperature equal to or higher than the strain point of the glass substrate used.

  By forming the thermal oxide film 266, the thickness of the crystalline silicon film 263 becomes about 450 angstroms. In this heat treatment, when the heating temperature is 600 ° C. to 750 ° C., the treatment time (heating time) is 10 hours to 48 hours, typically 24 hours. Of course, this processing time may be set as appropriate depending on the thickness of the oxide film to be obtained. In this gettering, oxygen present in the crystalline silicon film plays an important role. That is, gettering of nickel element proceeds in the form of nickel oxide formed by combining oxygen and nickel.

  As described above, when the concentration of oxygen is excessive, it becomes a factor that inhibits crystallization of the amorphous silicon film 263 in the crystallization step shown in FIG. However, as mentioned above, its presence plays an important role in the nickel gettering process. Therefore, it is important to control the concentration of oxygen present in the amorphous silicon film as the starting film. In the above process, since nickel element is gettered in the oxide film to be formed, the nickel concentration in the oxide film is naturally higher than that in other regions.

  Further, a tendency for nickel element to increase was observed in the vicinity of the interface between the silicon film 265 and the thermal oxide film 266 on the thermal oxide film 266 side. This is considered to be because the region where gettering is mainly performed is on the oxide film side in the vicinity of the interface between the silicon film and the oxide film. In addition, it is considered that the gettering progresses in the vicinity of the interface due to the presence of stress and defects near the interface.

  Next, the oxide film 266 containing nickel at a high concentration was removed. The removal of the oxide film 266 is performed by wet etching using buffer hydrofluoric acid (other hydrofluoric acid-based etchants) or dry etching. Here, wet etching using buffer hydrofluoric acid is performed. Thus, as shown in FIG. 39E, a crystalline silicon film 267 with a reduced concentration of nickel contained was obtained.

  In addition, since the nickel element is contained in a relatively high concentration near the surface of the obtained crystalline silicon film 267, the etching of the oxide film 266 is further advanced to slightly exceed the surface of the crystalline silicon film 267. Etching is effective. It is also effective to further promote the crystallinity of the obtained crystalline silicon film 267 by irradiating the laser beam again after removing the thermal oxide film 266.

  That is, it is effective to perform laser light irradiation again after gettering of the nickel element. Therefore, in this example, a KrF excimer laser (wavelength 248 nm) was used as the laser light. As the laser light, a XeCl excimer laser (wavelength 308 nm) or other types of excimer lasers may be used. Moreover, it is good also as a structure which irradiates with an ultraviolet-ray and infrared rays instead of a laser beam.

<< Example 40 >>
This Example 40 is an example in which Cu is used as the metal element for promoting crystallization of silicon in the configuration shown in Example 39. In this case, cupric acetate [Cu (CH ₃ COO) ₂ ], cupric chloride (CuCl ₂ 2H ₂ O), or the like may be used as a solution for introducing Cu. In this embodiment, cupric chloride (CuCl ₂ 2H ₂ O) is used, and the others are the same as in Embodiment 39, as shown in FIG. 267 could be obtained.

<< Example 41 >>
Example 41 is an example in which crystal growth of a form different from Example 39 was performed. This embodiment relates to a method of performing crystal growth in a direction parallel to the substrate, called lateral growth, using a metal element that promotes crystallization of silicon. FIG. 40 shows a manufacturing process of this example.

  First, a silicon oxynitride film having a thickness of 3000 angstroms was formed as a base film 269 on a Corning 1737 glass substrate 268. Note that a quartz substrate or the like may be used instead of the glass substrate. Next, an amorphous silicon film 270 serving as a starting film for the crystalline silicon film was formed to a thickness of 600 angstroms by low pressure thermal CVD. As described above, the thickness of the amorphous silicon film is preferably 2000 angstroms or less. Note that a plasma CVD method may be used instead of the low pressure thermal CVD method.

  Next, a silicon oxide film (not shown) was formed to a thickness of 1500 angstroms and patterned to form a mask indicated by reference numeral 271. This mask has an opening in a region indicated by reference numeral 272. In the region where the opening 272 is formed, the amorphous silicon film 270 is exposed. The opening 272 has an elongated rectangular shape in the longitudinal direction from the depth of the drawing toward the front. The width of the opening 272 is suitably 20 μm or more, and the length in the longitudinal direction may be formed as required. In this embodiment, the width is 35 μm and the length is 2 cm.

  Next, as shown in Example 40, a nickel acetate aqueous solution containing 10 ppm of nickel element in terms of weight was applied. Then, spin drying was performed using a spinner (not shown) to remove excess solution. Thus, a state in which the nickel element was held in contact with the exposed surface of the amorphous silicon film 270 was realized as indicated by a dotted line 273 in FIG.

  Next, heat treatment was performed at a temperature of 640 ° C. for 4 hours in a nitrogen atmosphere containing 3% by volume of hydrogen and containing as little oxygen as possible. Then, crystal growth proceeded in a direction parallel to the substrate 268 as indicated by 274 in FIG. This crystal growth proceeds from the region of the opening 272 into which nickel element is introduced toward the periphery. The crystal growth in the direction parallel to the substrate is referred to as lateral growth or lateral growth in this specification.

  Under the conditions as shown in this embodiment, this lateral growth can be performed over 100 μm or more. Thus, a silicon film 275 having a laterally grown region was obtained. In the region where the opening 272 is formed, crystal growth in a vertical direction called vertical growth proceeds from the surface of the silicon film toward the base interface.

  Next, the mask 271 made of a silicon oxide film for selectively introducing nickel element was removed to obtain the state shown in FIG. In this state, the silicon film 275 includes a vertical growth region, a lateral growth region, and a region (amorphous state) where crystal growth has not been achieved. In this state, nickel element is unevenly distributed in the film. In particular, the nickel element is present at a relatively high concentration in the region where the opening 272 is formed and the tip portion of the crystal growth indicated by 274.

  Next, laser light irradiation was performed. Here, in the same manner as in Example 39, irradiation with KrF excimer laser was performed to diffuse the unevenly distributed nickel element so that gettering can be easily performed in the subsequent gettering step. After the laser light irradiation was completed, heat treatment at a temperature of 650 ° C. was performed for 12 hours in an atmosphere of 100% oxygen.

  In this step, an oxide film 276 containing nickel element at a high concentration is formed, and at the same time, the nickel element concentration in the crystalline silicon film 275 can be relatively reduced. In this embodiment, a thermal oxide film indicated by reference numeral 276 is formed to a thickness of 100 angstroms. The thermal oxide film contains a high concentration of nickel element gettered by the film formation.

  Further, since the thermal oxide film 276 is formed, the crystalline silicon film 275 has a thickness of about 500 angstroms. Next, the thermal oxide film 276 containing nickel element at a high concentration was removed. The crystalline silicon film in this state has a concentration distribution such that nickel element exists at a high concentration toward the surface of the crystalline silicon film. This state is due to the fact that nickel element is gettered into the thermal oxide film when the thermal oxide film 276 is formed.

  Therefore, after removing the thermal oxide film 276, it is useful to further etch the surface of the crystalline silicon film to remove the region where the nickel element is present at a high concentration. That is, by etching the surface of the crystalline silicon film in which nickel element is present at a high concentration, a crystalline silicon film having a further reduced nickel element concentration can be obtained. However, in this case, it is necessary to consider the film thickness of the finally obtained crystalline silicon film.

Next, by patterning, a pattern 277 composed of a lateral growth region was formed. In this manner, the concentration of nickel element remaining in the pattern 277 made of the lateral growth region can be made lower than that in the case of the embodiment 39. This is also caused by the fact that the concentration of the metal element contained in the lateral growth region is low in the first place. Specifically, the concentration of nickel element in the pattern 277 made of the lateral growth region can be easily set to an order of 10 ¹⁷ cm ⁻³ or less.

  Further, when the thin film transistor is formed by using the lateral growth region, it is higher than that in the case of using the vertical growth region as shown in Example 39 (in the case of Example 39, the entire surface grows vertically). A semiconductor device having mobility can be obtained. Note that it is useful to remove the nickel element existing on the pattern surface by further performing an etching process after forming the pattern shown in FIG.

  After forming the pattern 277 as described above, a thermal oxide film 278 was formed. The thermal oxide film 278 was formed to a thickness of 100 Å by performing heat treatment in an oxygen atmosphere at a temperature of 650 ° C. for 12 hours. If this thermal oxide film constitutes a thin film transistor, it becomes a part of the gate insulating film later. Then, if a thin film transistor is to be manufactured, a silicon oxide film is formed by plasma CVD or the like so as to cover the thermal oxide film 278, and a gate insulating film is formed together with the thermal oxide film 278.

<< Example 42 >>
This embodiment 42 is an example of manufacturing a thin film transistor disposed in a pixel region of an active matrix liquid crystal display device or an active matrix EL display device. FIG. 41 is a diagram showing a manufacturing process of this example.

  First, a crystalline silicon film was formed on a glass substrate by the steps shown in Example 39 and Example 41. Since the subsequent steps are the same for both, a case where a crystalline silicon film is obtained with the structure shown in Example 39 will be described below. The crystalline silicon film was patterned to obtain the state shown in FIG. In this state, 280 is a glass substrate, 281 is a base film, and 282 is an active layer composed of a crystalline silicon film. After obtaining the state shown in FIG. 41A, plasma treatment was performed in a reduced pressure atmosphere in which oxygen and hydrogen were mixed. This plasma was generated by high frequency discharge.

  By this plasma treatment, organic substances present on the exposed surface of the active layer 282 are removed. Precisely, the organic substance adsorbed on the surface of the active layer is oxidized by oxygen plasma, and the oxidized organic substance is reduced and vaporized by hydrogen plasma. In this way, organic substances present on the exposed surface of the active layer 282 are removed. This removal of organic substances is very effective in suppressing the presence of fixed charges on the surface of the active layer 282. Fixed charges resulting from the presence of organic substances hinder the operation of the device and cause instability of characteristics, and it is very useful to reduce the presence thereof.

After removing the organic matter, thermal oxidation was performed in an oxygen atmosphere at a temperature of 640 ° C. to form a thermal oxide film 279 having a thickness of 100 Å. This thermal oxide film has high interface characteristics with the semiconductor layer, and will later constitute a part of the gate insulating film. In this way, the state shown in FIG. Thereafter, a silicon oxynitride film 283 constituting a gate insulating film was formed to a thickness of 1000 angstroms. As a film forming method, a plasma CVD method using a mixed gas of oxygen, silane, and N ₂ O, a plasma CVD method using a mixed gas of TEOS and N ₂ O, or the like is used. A mixed gas of silane and N ₂ O was used.

  This silicon oxynitride film 283 functions as a gate insulating film together with the thermal oxide film 279. In addition, it is effective to include a halogen element in the silicon oxynitride film. That is, by fixing the nickel element by the action of the halogen element, the insulating film of the gate insulating film is affected by the nickel element existing in the active layer (the same applies to other metal elements that promote crystallization of silicon). It is possible to prevent the function as a deterioration.

  The use of a silicon oxynitride film as the above film has a significance that a metal element hardly enters the gate insulating film because of its dense film quality. When a metal element enters (penetrates) into the gate insulating film, the function as the insulating film is reduced, which causes instability and variations in characteristics of the thin film transistor. Note that a commonly used silicon oxide film can also be used as the gate insulating film.

  After forming the silicon oxynitride film 283 that functions as a gate insulating film, an aluminum film that functions as a gate electrode later was formed by a sputtering method. In this aluminum film (not shown, the pattern 284 is formed after patterning described later), 0.2% by weight of scandium was contained. The reason why scandium is contained in the aluminum film is to suppress generation of hillocks and whiskers in the subsequent process. Here, hillocks and whiskers mean that abnormal heating of aluminum occurs when heating is performed, and needle-like or stab-like protrusions are formed.

  After the aluminum film was formed, a dense anodic oxide film (not shown) was formed. This anodic oxide film was formed by using an ethylene glycol solution containing 3% by weight of tartaric acid as an electrolytic solution. That is, in this electrolytic solution, an anodic oxidation film having a dense film quality is formed on the surface of the aluminum film by performing anodization using the aluminum film as an anode and platinum as a cathode. The film thickness of the anodic oxide film having a dense film quality (not shown) is about 100 angstroms. This anodic oxide film has a role of improving adhesion with a resist mask to be formed later. The film thickness of the anodic oxide film can be controlled by the applied voltage during anodic oxidation.

  Next, after a resist mask 285 was formed, the aluminum film was patterned into a pattern indicated by 284. In this way, the state shown in FIG. Here, anodic oxidation was performed again. In this example, a 3% by weight oxalic acid aqueous solution was used as the electrolytic solution. In this electrolytic solution, a porous anodic oxide film denoted by reference numeral 287 is formed by performing anodization using the aluminum pattern 284 as an anode.

  In this step, an anodic oxide film 287 is selectively formed on the side surface of the aluminum pattern 284 because the resist mask 285 having high adhesion exists on the upper portion. This anodic oxide film can be grown to a thickness of several μm. Here, the film thickness was set to 6000 angstroms. The growth distance can be controlled by the anodic oxidation time.

  Next, after removing the resist mask 285, a dense anodic oxide film was formed again. That is, the anodic oxidation using the ethylene glycol solution containing 3% by weight of tartaric acid as an electrolytic solution was performed again. As a result, an anodic oxide film having a dense film quality is formed as indicated by reference numeral 288 because the electrolytic solution enters the porous anodic oxide film 287. The film thickness of this dense anodic oxide film 288 was 1000 angstroms. The film thickness was controlled by adjusting the applied voltage.

  Here, the exposed silicon oxynitride film 283 and the thermal oxide film 279 were etched. Dry etching was used for this etching. Next, the porous anodic oxide film 287 was removed using a mixed acid solution in which acetic acid, nitric acid and phosphoric acid were mixed. After obtaining the state shown in FIG. 41D in this way, impurity ions were implanted. Here, in order to manufacture an N-channel thin film transistor, P (phosphorus) ions are implanted by a plasma doping method. In this step, regions 290 and 294 that are heavily doped and regions 291 and 293 that are lightly doped are formed. The reason why it is formed in this way is that a part of the remaining silicon oxide film 289 functions as a semi-transmissive mask, and a part of the implanted ions is shielded there.

  Next, the region into which the impurity ions have been implanted is activated by irradiating laser light or strong light. Here, an infrared lamp is used. Thus, the source region 290, the channel formation region 292, the drain region 294, and the low-concentration impurity regions 291 and 293 are formed in a self-aligned manner. Here, what is denoted by reference numeral 293 is a region called an LDD (lightly doped drain) region.

  When the film thickness of the dense anodic oxide film 288 is increased to 2000 angstroms or more, an offset gate region can be formed outside the channel formation region 292 with the film thickness. In this embodiment, the offset gate region is formed, but since the size thereof is small, the contribution due to its existence is small, and the drawing becomes complicated, so it is not shown in the drawing.

  Next, a silicon oxide film, a silicon nitride film, or a stacked film thereof is formed as the interlayer insulating film 295. Here, a silicon nitride film was formed. The interlayer insulating film 295 may be formed by forming a layer made of a resin material on a silicon oxide film or a silicon nitride film. Further, contact holes were formed, and a source electrode 296 and a drain electrode 297 were formed. Thus, the thin film transistor shown in FIG. 39E was completed.

Example 43
This example 43 relates to a method of forming the gate insulating film 283 in the configuration shown in the actual example 42. When a quartz substrate or a glass substrate having high heat resistance is used as the substrate, a thermal oxidation method can be used as a method for forming the gate insulating film. In this example, a thermal oxidation method was used to form the gate insulating film 283, and the other steps were performed in the same manner as in Example 42 to obtain a thin film transistor having the structure shown in FIG.

  The thermal oxidation method can make the film quality dense and is useful for obtaining a thin film transistor having stable characteristics. In other words, an oxide film formed by a thermal oxidation method is dense as an insulating film and can reduce the movable charges existing therein, and thus is one of the optimum gate insulating films.

<< Example 44 >>
Example 44 is an example in which a thin film transistor was manufactured through a process different from that shown in FIG. FIG. 42 is a diagram showing a manufacturing process of this example. First, a crystalline silicon film was formed on a glass substrate by the steps described in Example 39 (FIG. 38) and Example 41 (FIG. 40), respectively. The following steps are the same for both. Next, by patterning it, the state shown in FIG. 42 (A) was obtained.

After obtaining the state shown in FIG. 42A, plasma treatment was performed in a mixed reduced pressure atmosphere of oxygen and hydrogen. In the state shown in FIG. 42A, 299 is a glass substrate, 300 is a base film, and 301 is an active layer composed of a crystalline silicon film. Reference numeral 298 denotes a thermal oxide film formed again after removal of the thermal oxide film for gettering. After obtaining the state shown in FIG. 42A, a silicon oxynitride film 302 constituting a gate insulating film was formed to a thickness of 1000 angstroms. For the film formation, a plasma CVD method using a mixed gas of oxygen, silane, and N ₂ O or a plasma CVD method using a mixed gas of TEOS and N ₂ O is used. A mixed gas with N ₂ O was used.

  The silicon oxynitride film 302 forms a gate insulating film together with the thermal oxide film 298. Note that a silicon oxide film can be used in addition to the silicon oxynitride film. After forming the silicon oxynitride film 302 functioning as a gate insulating film, an aluminum film (not shown, which becomes a pattern 304 after patterning described later) functioning as a gate electrode later was formed by sputtering. This aluminum film contained 0.2% by weight of scandium.

  After forming the aluminum film, a dense anodic oxide film (not shown) was formed. This anodic oxide film was implemented by using an ethylene glycol solution containing 3% by weight of tartaric acid as an electrolytic solution. That is, in this electrolytic solution, an anodic oxidation film having a dense film quality is formed on the surface of the aluminum film by performing anodization using the aluminum film as an anode and platinum as a cathode. The film thickness of the anodic oxide film having a dense film quality (not shown) is about 100 angstroms. This anodic oxide film has a role of improving adhesion with a resist mask to be formed later. The film thickness of the anodic oxide film can be controlled by adjusting the applied voltage during anodic oxidation.

  Next, a resist mask 303 was formed. The aluminum film was patterned into a pattern indicated by 304, and then anodized again. Here, a 3% by weight oxalic acid aqueous solution was used as the electrolytic solution. In this electrolytic solution, a porous anodic oxide film denoted by reference numeral 305 is formed by anodizing using the aluminum pattern 304 as an anode.

  In this step, the anodic oxide film 305 is selectively formed on the side surface of the aluminum pattern because the resist mask 303 having high adhesion exists on the upper portion. This anodic oxide film 305 can be grown to a thickness of several μm. Here, the film thickness was set to 6000 angstroms. The growth distance can be controlled by the anodic oxidation time.

  Next, after removing the resist mask 303, a dense anodic oxide film was formed again. That is, the anodic oxidation using the ethylene glycol solution containing 3% by weight of tartaric acid as an electrolytic solution was performed again. Then, an anodic oxide film having a dense film quality is formed as indicated by reference numeral 306 because the electrolytic solution enters the porous anodic oxide film 305. Here, the first impurity ions were implanted. Note that this step may be performed after the resist mask 303 is removed. By this impurity ion implantation, a source region 307 and a drain region 309 are formed. At this time, impurity ions are not implanted into the region indicated by reference numeral 308.

  Next, the porous anodic oxide film 305 was removed using a mixed acid obtained by mixing acetic acid, nitric acid and phosphoric acid. In this way, the state shown in FIG. Thereafter, impurity ions are implanted again. The impurity ions are implanted under the light doping conditions from the first impurity ion implantation conditions. In this step, lightly doped regions 310 and 311 are formed, and a region indicated by 312 becomes a channel forming region.

  Next, the region into which the impurity ions have been implanted is activated by irradiation with laser light or strong light. Here, laser light is used. Thus, the source region 307, the channel formation region 312, the drain region 309, and the low concentration impurity regions 310 and 311 are formed in a self-aligned manner. Here, a region denoted by reference numeral 311 is a region called an LDD (lightly doped drain) region.

  Next, a silicon oxide film, a silicon nitride film, or a stacked film thereof is formed as the interlayer insulating film 313. Here, both laminated films were formed. The interlayer insulating film may be formed by forming a layer made of a resin material on a silicon oxide film or a silicon nitride film. Then, contact holes were formed, and a source electrode 314 and a drain electrode 315 were formed. Thus, the thin film transistor shown in FIG. 42E was completed.

Example 45
The present embodiment 45 is an example in which an N channel type thin film transistor and a P channel type thin film transistor are configured in a complementary manner. FIG. 43 is a diagram showing a process of this example. The configuration shown in this embodiment can be used for various thin film integrated circuits integrated on an insulating surface, for example. For example, it can be used for a peripheral drive circuit of an active matrix liquid crystal display device.

  First, a silicon oxide film or a silicon oxynitride film was formed as a base film 318 over a glass substrate 317 as illustrated in FIG. Of these, a silicon oxynitride film is preferably used, but this was used in this embodiment. Next, an amorphous silicon film (not shown) is formed by a plasma CVD method or a low pressure thermal CVD method. Here, the low pressure thermal CVD method is used. Further, this amorphous silicon film was transformed into a crystalline silicon film by the method shown in Example 39.

  Next, plasma treatment was performed in a mixed atmosphere of oxygen and hydrogen, and the obtained crystalline silicon film was patterned to obtain active layers 319 and 320. In this way, the state shown in FIG. Here, in order to suppress the influence of carriers moving on the side surface of the active layer, heating is performed at a temperature of 650 ° C. for 10 hours in a nitrogen atmosphere containing 3% by volume of HCl in the state shown in FIG. Processed.

  The presence of a trap level due to the presence of a metal element on the side surface of the active layer leads to deterioration of the OFF current characteristics. Therefore, the processing shown here should be performed to reduce the level density on the side surface of the active layer. Is useful. Next, a thermal oxide film 316 and a silicon oxynitride film 321 constituting a gate insulating film were formed. Here, when quartz is used as the substrate, it is desirable to form the gate insulating film only with the thermal oxide film by using the thermal oxidation method described above.

  Next, an aluminum film (not shown, which is to be a pattern after patterning) (not shown) for forming a gate electrode later was formed to a thickness of 4000 angstroms. In addition to an aluminum film, an anodizable metal (for example, tantalum) can be used. After forming the aluminum film, an extremely thin dense anodic oxide film was formed on the surface by the method described above.

  Next, a resist mask (not shown) was placed on the aluminum film, and the aluminum film was patterned. Further, anodization was performed using the obtained aluminum pattern as an anode to form porous anodic oxide films 324 and 325. The thickness of the porous anodic oxide film was 5000 angstroms.

  Here, anodization was performed again under the conditions for forming a dense anodized film, and dense anodized films 326 and 327 were formed. Here, the dense anodic oxide films 326 and 327 have a thickness of 800 angstroms. In this way, the state shown in FIG. Next, the exposed silicon oxide film 321 and the thermal oxide film 316 were removed by dry etching to obtain the state shown in FIG.

  Thereafter, the porous anodic oxide films 324 and 325 were removed using a mixed acid solution in which acetic acid, nitric acid and phosphoric acid were mixed. In this way, the state shown in FIG. Next, resist masks were alternately arranged, and P (phosphorus) ions were implanted into the left thin film transistor, and B (boron) ions were implanted into the right thin film transistor. By this impurity ion implantation, a source region 330 and a drain region 333 having a high concentration N-type were formed in a self-aligned manner.

  At the same time, a weak N-type region 331 doped with P ions at a low concentration is formed at the same time, and a channel formation region 332 is formed at the same time. The reason why the weak N-type region indicated by reference numeral 331 is formed is that the remaining gate insulating film 328 exists. That is, P ions that have passed through the gate insulating film 328 are partially shielded by the gate insulating film 328.

  Further, by the same principle and method as described above, the source region 337 and the drain region 334 having strong P-type are formed in a self-aligned manner, the low concentration impurity region 336 is formed at the same time, and the channel forming region 335 is formed at the same time. The If the dense anodic oxide films 326 and 327 are as thick as 2000 angstroms, an offset gate region can be formed in contact with the channel formation region with that thickness.

  In the present embodiment, since the dense anodic oxide films 326 and 327 are as thin as 1000 angstroms or less, their presence can be ignored. Next, laser light was irradiated to anneal the region into which impurity ions were implanted. Note that intense light irradiation may be performed instead of laser light. Then, as shown in FIG. 43E, a silicon nitride film 338 and a silicon oxide film 339 are formed as interlayer insulating films, and the thicknesses thereof are each 1000 angstroms. Note that in this case, the silicon oxide film 339 is not necessarily formed.

  Here, the thin film transistor is covered with the silicon nitride film. Since the silicon nitride film is dense and has good interface characteristics, the reliability of the thin film transistor can be improved with such a structure. Further, an interlayer insulating film 340 made of a resin material was formed using a spin coat method. Here, the thickness of the interlayer insulating film 340 is set to 1 μm.

  Then, contact holes were formed to form a source electrode 341 and a drain electrode 342 of the left N-channel thin film transistor, and at the same time, a source electrode 343 and a drain electrode 342 of the right thin film transistor were formed. Here, the drain electrode 342 is arranged in common for both. Thus, a thin film transistor circuit having a complementary CMOS structure was formed.

  In the structure shown in this embodiment, a structure in which the thin film transistor is covered with a silicon nitride film and further covered with a resin material can be obtained. This configuration can be made highly durable such that mobile ions and moisture do not easily enter. Further, when a multilayer wiring is formed, it is possible to prevent a capacitance from being formed between the thin film transistor and the wiring.

Example 46
Example 46 is an example in which nickel element was directly introduced into the surface of the base film in the step shown in Example 39. In this case, the nickel element is held in contact with the lower surface of the amorphous silicon film. In this embodiment, after the base film is formed, nickel element is introduced using a nickel acetate aqueous solution, and the nickel element is first held in contact with the surface of the base film.

  With respect to the other steps, as in the case of Example 39, as shown in FIG. 39E, a crystalline silicon film 267 with a reduced concentration of nickel contained was obtained. As a method for introducing nickel element, in addition to a method using a solution as in this embodiment, a sputtering method, a CVD method, and an adsorption method can be used. In addition, when a metal element that promotes crystallization of silicon other than nickel is used, a crystalline silicon film in which the concentration of the metal is similarly reduced can be obtained.

Example 47
In this example 47, an island made of a crystalline silicon film obtained by irradiating laser light in the state of FIG. 40E, FIG. 41A, or FIG. This is an example in which the crystallinity of the pattern is improved. When laser light is irradiated in the state of FIG. 40E, FIG. 41A, or FIG. 42A, a predetermined annealing effect can be obtained with a relatively low irradiation energy density. This is considered to be because the energy efficiency used for annealing increases because laser energy is irradiated to a small area.

Example 48
The present embodiment 48 is an example in which the device is devised for patterning the active layer of the thin film transistor in order to enhance the annealing effect by the laser light irradiation. FIG. 44 is a diagram showing a manufacturing process of a thin film transistor in this example. First, a silicon oxide film 345 was formed as a base film on a Corning 1737 glass substrate 344. A silicon oxynitride film can also be used as the base film.

  Next, an amorphous silicon film (not shown) was formed to a thickness of 500 angstroms. A low pressure thermal CVD method was used for film formation. This amorphous silicon film later becomes a crystalline silicon film 346 through a crystallization step. Next, an amorphous silicon film (not shown) was crystallized by the methods shown in Example 39 (see FIG. 39) and Example 41 (see FIG. 40) to obtain a crystalline silicon film.

  In this way, the state shown in FIG. Hereinafter, the case according to Example 39 will be mainly described, but the same applies to the case according to Example 41. After obtaining the state shown in FIG. 44A, a crystalline silicon film 346 was formed on the glass substrate in accordance with the manufacturing process of Example 39 (FIG. 39). That is, the amorphous silicon film was crystallized by a heat treatment using nickel element, and a crystalline silicon film 346 was obtained. The heat treatment conditions here were a temperature of 620 ° C. and heating for 4 hours.

  After obtaining the crystalline silicon film, a pattern for forming an active layer of the thin film transistor was formed. In this case, the cross-sectional shape of this pattern is a shape as indicated by 347 in FIG. In this manner, the pattern 347 as illustrated in FIG. 44B is formed in order to suppress the deformation of the pattern shape in the subsequent processing step by laser light irradiation.

  As described above, when laser light is applied to the pattern 258 made of a normal island-like silicon film formed on the base 257 as shown in FIG. 38A, as shown in FIG. 38B. The convex part 260 will be formed in the edge part of the pattern 259 after irradiation of a laser beam. This is considered to occur because the energy of the irradiated laser beam is concentrated on the edge portion of the pattern where there is no heat escape.

  The convex portion 260 formed by this phenomenon causes a defect in wiring that later constitutes the thin film transistor and a malfunction of the thin film transistor. Therefore, in the structure shown in this embodiment, the active layer pattern 347 has a cross-sectional shape as shown in FIG. With such a structure, it is possible to prevent the silicon film pattern from having a shape as illustrated in FIG. A pattern as indicated by reference numeral 347 can be realized by utilizing isotropic dry etching at the time of patterning and controlling the dry etching conditions.

  Here, it is preferable that the angle of the portion indicated by reference numeral 348 with respect to the surface of the base film 345 is 20 ° to 50 °. Setting the angle of the portion indicated by reference numeral 348 to be less than 20 ° is not preferable because an increase in the area occupied by the active layer and difficulty in forming the active layer increase. Also, setting the angle indicated by the reference numeral 348 to an angle exceeding 50 ° is also not preferable because the effect of suppressing the formation of the convex portion 260 as shown in FIG. 38B is reduced. .

  After obtaining a pattern having a shape indicated by reference numeral 347 in FIG. 44B (to be an active layer later), laser light irradiation was performed as shown in FIG. By this step, nickel element which is locally solidified in the pattern 347 can be diffused and its crystallinity can be promoted. Next, after the laser light irradiation was completed, heat treatment was performed in an oxygen atmosphere, so that a thermal oxide film 349 was formed. Here, a thermal oxide film 349 having a thickness of 100 Å is formed by performing a heat treatment at a temperature of 650 ° C. for 12 hours in an atmosphere of 100% oxygen.

  The thermal oxide film 349 is gettered with the nickel element contained in the pattern 347 by the action of oxygen. At this time, since the mass of the nickel element is destroyed by the laser beam irradiation in the previous step, gettering of the nickel element is effectively performed. In addition, when halogen is contained as an atmosphere for the heat treatment, gettering of nickel element can be performed more effectively.

  Further, when the configuration shown in this embodiment is employed, gettering from the side surface of the pattern 347 is also performed. This is useful in improving the OFF current characteristics and reliability of the finally completed thin film transistor. This is because the presence of nickel element (the same applies to other metal elements that promote crystallization of silicon) present on the side surface of the active layer is greatly related to an increase in OFF current and instability of characteristics.

  After the gettering thermal oxide film 349 shown in FIG. 44D was formed, the thermal oxide film 349 was removed. In this way, the state shown in FIG. When a silicon oxide film is employed as the base film 345 as in this embodiment, there is a concern that the silicon oxide film 345 is etched in the step of removing the thermal oxide film 349. However, as shown in this embodiment, when the thickness of the thermal oxide film 349 is as thin as about 100 angstrom, this is not a big problem.

  After obtaining the state shown in FIG. 44E, a new thermal oxide film 350 was formed. This thermal oxide film 350 was formed by heat treatment in an atmosphere of 100% oxygen. Here, the thermal oxide film 350 is formed to a thickness of 100 Å by heat treatment in an oxygen atmosphere at a temperature of 650 ° C. for 4 hours. The thermal oxide film 350 is effective in suppressing the surface of the pattern 347 from becoming rough when the laser beam is irradiated later, and constitutes a part of the gate insulating film later.

  Since the thermal oxide film 350 has very good interface characteristics with the crystalline silicon film, it is useful to use it as a part of the gate insulating film. Note that after the thermal oxide film 350 is formed, laser light irradiation may be performed again. Thus, the concentration of nickel element was reduced, and a crystalline silicon film 347 having high crystallinity was obtained. Thereafter, a thin film transistor is manufactured through steps as shown in FIGS.

Example 49
The present Example 49 is an example about the device in the case of applying heat treatment at a temperature equal to or higher than the strain point of the glass substrate. In the present invention, after crystallizing amorphous silicon using a metal element that promotes crystallization of silicon, the metal element is gettered. This gettering step is preferably performed at a temperature as high as possible. .

  For example, even when Corning 1737 glass (strain point 667 ° C.) is used as a substrate, the temperature at which nickel element gettering is performed by forming a thermal oxide film is 700 ° C. rather than 650 ° C., for example. Higher gettering action can be obtained. However, in this case, if the heating temperature for forming the thermal oxide film is 700 ° C., the glass substrate is deformed.

  The present embodiment is an example in which this problem is solved. That is, in the configuration shown in this example, the glass substrate was placed on a surface plate made of quartz with guaranteed flatness, and heat treatment was performed in this state. In this way, the flatness of the softened glass substrate is also maintained by the flatness of the surface plate. In this case, it is important to perform cooling in a state where the glass substrate is disposed on the surface plate. By adopting such a configuration, heat treatment can be performed even at a temperature equal to or higher than the strain point of the glass substrate.

Example 50
Example 50 is an example in which a crystalline silicon film is obtained on a quartz substrate using nickel element. In this example, first, the amorphous silicon film formed on the quartz substrate was transformed into a crystalline silicon film having high crystallinity by the action of nickel element.

  Next, heat treatment was performed in an oxidizing atmosphere to which HCl was added to form a thermal oxide film. At this time, nickel element remaining in the crystalline silicon film is gettered by the action of chlorine (Cl) in the obtained crystalline silicon film. After the gettering, the thermal oxide film containing nickel element at a high concentration was removed. Thus, a crystalline silicon film having a low nickel element concentration while having high crystallinity on the quartz substrate was obtained.

  FIG. 45 is a diagram showing a manufacturing process of this example. First, a silicon oxynitride film 352 having a thickness of 5000 angstroms was formed as a base film on a quartz glass substrate 351. The base film 352 is preferably about 5000 angstroms or more in order to have a function of reducing a difference in thermal expansion coefficient between the quartz glass substrate 351 and a silicon film to be formed later.

The silicon oxynitride film 352 was formed by a plasma CVD method using silane, N ₂ O gas, and oxygen as source gases. Instead of this, a plasma CVD method using TEOS gas and N ₂ O gas may be used. It is effective to add a trace amount of a halogen element typified by chlorine in the base film 352. In this manner, a metal element that promotes crystallization of silicon existing in the semiconductor layer can be gettered by the halogen element in a later step.

  It is also effective to add a hydrogen plasma treatment after forming the base film. In addition, it is effective to perform plasma treatment in an atmosphere in which oxygen and hydrogen are mixed. This is effective in removing the carbon component adsorbed on the surface of the base film and improving the interface characteristics with the semiconductor film to be formed later. Next, an amorphous silicon film 353 to be a crystalline silicon film later was formed to a thickness of 1500 angstrom by low pressure thermal CVD. The reason why the low pressure thermal CVD method is used is that the crystalline silicon film obtained later is superior in film quality, specifically, the film quality is dense. As a method other than the low pressure thermal CVD method, a plasma CVD method can be used.

The amorphous silicon film produced here preferably has an oxygen concentration in the film of 5 × 10 ¹⁷ cm ⁻³ to 2 × 10 ¹⁹ cm ⁻³ . This is because oxygen plays an important role in the subsequent gettering step of a metal element (metal element that promotes crystallization of silicon). However, when the oxygen concentration is higher than the above concentration range, care must be taken because crystallization of the amorphous silicon film is inhibited. Further, other impurity concentrations, for example, nitrogen and carbon impurity concentrations should be as low as possible. Specifically, it is necessary to set them to a concentration of 2 × 10 ¹⁹ cm ⁻³ or less.

  The thickness of the amorphous silicon film can be selected from a range of about 1000 to 5000 angstroms. Next, nickel element was introduced to crystallize the amorphous silicon film 353. Here, nickel element was introduced by applying a nickel acetate aqueous solution containing 10 ppm (weight conversion) nickel on the surface of the amorphous silicon film 353. As a method for introducing nickel element, in addition to the above method using a solution, a sputtering method, a CVD method, a plasma treatment or an adsorption method can be used. Of these, the method using the above solution is useful in that it is simple and the concentration of the metal element can be easily adjusted.

  By applying the nickel acetate solution, a water film of an aqueous nickel acetate solution is formed as indicated by 354 in FIG. After obtaining this state, excess solution was blown off using a spinner (not shown). In this manner, the nickel element was held in contact with the surface of the amorphous silicon film 353.

  In view of residual impurities in the subsequent heating step, for example, nickel sulfate is preferably used instead of the nickel acetate salt solution. This is because the nickel acetate salt solution contains carbon, which is feared to carbonize and remain in the film in the subsequent heating step. The amount of nickel element introduced can be adjusted by adjusting the concentration of nickel element in the solution.

Next, in the state shown in FIG. 45B, heat treatment is performed at a temperature of 750 ° C. to 1100 ° C., and the amorphous silicon film 353 is crystallized, so that a crystalline silicon film 355 is obtained. Here, the heat treatment at 900 ° C. for 4 hours was performed in a nitrogen atmosphere (in a reducing atmosphere) in which 2% by volume of hydrogen was mixed. The reason why the atmosphere is reduced in this crystallization process by heat treatment is to prevent the formation of oxide during the heat treatment process. Specifically, this is to prevent nickel and oxygen from reacting to form NiO _x on the film surface or in the film.

  Oxygen is combined with nickel in a later gettering step and contributes greatly to the gettering of nickel. However, it has been found that the combination of oxygen and nickel at this crystallization stage inhibits crystallization. Therefore, in the crystallization process by heating, it is important to suppress the formation of oxide as much as possible.

  The oxygen concentration in the atmosphere for performing the heat treatment for crystallization needs to be on the order of ppm, preferably 1 ppm or less. Moreover, as gas which occupies most of the atmosphere which performs the heat processing for the said crystallization, inert gas, such as argon, or those mixed gas containing nitrogen other than nitrogen can be used. After obtaining the crystalline silicon film 355, patterning was performed to form an island-shaped region 356 that later becomes an active layer of the thin film transistor.

  Next, heat treatment was performed again in the process illustrated in FIG. This heat treatment is performed to form a thermal oxide film for gettering the nickel element. Here, a heat treatment at a temperature of 950 ° C. was performed for 1 hour and 30 minutes in a nitrogen atmosphere containing 5% by volume of oxygen and 3% by volume of HCl with respect to this oxygen. As a result of this step, a thermal oxide film 357 was formed to a thickness of 200 angstroms.

  As described above, this step is a step for removing the nickel element intentionally introduced at an early stage for crystallization of silicon from the crystalline silicon film 356 formed in an island pattern. This heat treatment is performed at a temperature higher than the heat treatment performed for the above-described crystallization. This is an important condition for effectively performing gettering of nickel element. Note that although it can be performed at a temperature equal to or lower than the heat treatment temperature performed for crystallization, the effect is small. These points are the same when other metal elements that promote crystallization of silicon are used.

  By forming the thermal oxide film 357, the film thickness of the crystalline silicon film 356 formed in an island pattern is reduced by about 100 angstroms. In this gettering, oxygen present in the crystalline silicon film plays an important role. That is, nickel element gettering proceeds in a form in which chlorine element acts on nickel oxide formed by combining oxygen and nickel.

  As described above, if the concentration of oxygen is excessive, it becomes an element that inhibits crystallization of the amorphous silicon film 353 in the crystallization step shown in FIG. However, as mentioned above, its presence plays an important role in the nickel gettering process. Therefore, it is important to control the concentration of oxygen present in the amorphous silicon film serving as the starting film. In the above process, since nickel element is gettered in the oxide film to be formed, the nickel concentration in the oxide film is naturally higher than that in other regions.

  Further, a tendency for nickel element to increase was observed near the thermal oxide film 357 side at the interface between the crystalline silicon film 356 and the thermal oxide film 357. It is considered that this is because the region where gettering is mainly performed is on the oxide film side in the vicinity of the interface between the crystalline silicon film and the oxide film. Moreover, it is considered that the gettering progresses in the vicinity of the interface between the two due to the presence of stress and crystal defects in the vicinity of the interface.

In this embodiment, an example using chlorine (Cl) as a halogen element is shown, and an example using HCl as an introduction method thereof is shown. However, as the gas other than HCl, one type selected from HF, HBr, Cl ₂ , F ₂ and Br ₂ or a mixed gas of a plurality of types thereof can be used. In general, a hydride of halogen can be used. These gases are 0.25 to 5% if the content (volume content) in the atmosphere is HF, 1 to 15% if HBr, 0.25 to 5% if Cl ₂ , F ₂ is preferably 0.125 to 2.5%, and Br ₂ is preferably 0.5 to 10%.

  If the concentration is lower than the above range, a significant effect cannot be obtained. If the concentration exceeds the above range, the surface of the silicon film is roughened. Next, a thermal oxide film was formed by heat treatment in an oxidizing atmosphere containing a halogen element as described above, and then the thermal oxide film 357 containing nickel at a high concentration was removed. The thermal oxide film 357 is removed by wet etching or dry etching using buffer hydrofluoric acid (other hydrofluoric acid-based etchant). In this embodiment, wet etching using buffer hydrofluoric acid was used.

  Thus, as shown in FIG. 45E, an island-shaped pattern 356 made of a crystalline silicon film with a reduced concentration of nickel contained was obtained. Here, since the nickel element is contained at a relatively high concentration in the vicinity of the surface of the obtained crystalline silicon film 356, the etching of the oxide film 357 is further advanced to slightly exceed the surface of the crystalline silicon film 356. Etching is effective.

  It is also effective to further promote the crystallinity of the crystalline silicon film 356 by irradiating laser light or strong light after removing the thermal oxide film 357. That is, it is effective to perform laser light irradiation or strong light irradiation after nickel element gettering. As a laser beam to be used, a KrF excimer laser (wavelength 248 nm), a XeCl excimer laser (wavelength 308 nm), or other types of excimer lasers can be used. Moreover, as strong light, it can carry out by irradiation of an ultraviolet-ray or infrared rays, for example.

  In addition, it is effective to form a thermal oxide film (not shown) by heat treatment again after obtaining the state shown in FIG. This thermal oxide film functions as a part of the gate insulating film or as the gate insulating film when the thin film transistor is formed later. Since the thermal oxide film can improve the interface characteristics with the active layer made of crystalline silicon, the thermal oxide film is optimal for constituting the gate insulating film.

Example 51
This Example 51 is an example in which Cu is used as the metal element for promoting the crystallization of silicon in the configuration shown in the Example 50. In this case, cupric acetate [Cu (CH ₃ COO) ₂ ], cupric chloride (CuCl ₂ 2H ₂ O), or the like may be used as a solution for introducing Cu. In this example, cupric acetate [Cu (CH ₃ COO) ₂ ] was used, and the other steps were performed in the same manner as in Example 50 to obtain the state shown in FIG.

Example 52
The present Example 52 is an example in which crystal growth of a form different from that of the Example 50 was performed. This embodiment relates to a method of performing crystal growth in a direction parallel to the substrate, called lateral growth, using a metal element that promotes crystallization of silicon.

  FIG. 46 shows a manufacturing process of this example. First, a silicon oxynitride film having a thickness of 3000 angstroms was formed as a base film 359 on a quartz substrate 358. Next, an amorphous silicon film 360 serving as a starting film for the crystalline silicon film was formed to a thickness of 2000 angstrom by low pressure thermal CVD. Note that a plasma CVD method may be used instead of the low pressure thermal CVD method.

  Next, a silicon oxide film (not shown) was formed to a thickness of 1500 angstroms and patterned to form a mask indicated by reference numeral 361. The mask has an opening in a region indicated by reference numeral 362. In the region where the opening 362 is formed, the amorphous silicon film 360 is exposed. The opening 362 has a rectangular shape elongated in the longitudinal direction from the depth of the drawing to the front side. The width of the opening 362 is suitably 20 μm or more, and the length in the longitudinal direction may be formed with a required length. Here, the width was 20 μm and the length was 1 cm.

  Next, an aqueous nickel acetate solution containing 10 ppm of nickel element in terms of weight was applied to the mask 361 and the opening 362, and then spin drying was performed using a spinner (not shown) to remove excess solution. Thus, as indicated by a dotted line 363 in FIG. 46A, a state in which the nickel element is held in contact with the exposed surface of the amorphous silicon film 360 is realized.

  Next, heat treatment was performed at a temperature of 800 ° C. for 4 hours in a nitrogen atmosphere containing 2% by volume of hydrogen and containing as little oxygen as possible. Then, crystal growth in a direction parallel to the substrate 358 progressed as indicated by 364 in FIG. This crystal growth proceeds from the region of the opening 362 into which nickel element is introduced toward the periphery. Such crystal growth in a direction parallel to the substrate is referred to as lateral growth or lateral growth in this specification.

  Under the conditions as shown in this embodiment, this lateral growth can be performed over 100 μm or more. Thus, a silicon film having a laterally grown region was obtained. In the region where the opening 362 is formed, crystal growth in the vertical direction called vertical growth proceeds from the surface of the silicon film toward the base interface.

  Next, after removing the mask 361, further patterning is performed, and as shown in FIG. 46C, an island made of a crystalline silicon film that has grown in a direction parallel to the substrate (that is, laterally grown). A pattern 366 was formed. Thereafter, heat treatment was performed at a temperature of 950 ° C. for 1 hour and 30 minutes in a nitrogen atmosphere containing 10% by volume of oxygen and 3% by volume of HCl with respect to oxygen.

  As a result, a thermal oxide film denoted by reference numeral 367 was formed to a thickness of 200 angstroms. FIG. 46 (D) shows this state. In this step, an oxide film 367 containing nickel element at a high concentration (that is, gettering nickel element) is formed, and thereby the concentration of nickel element in the silicon film 367 is relatively reduced. .

  Therefore, the thermal oxide film 367 contains a high concentration of nickel element gettered according to the film formation. Further, by forming the thermal oxide film 367, the crystalline silicon film 366 has a thickness of about 500 angstroms. Next, the thermal oxide film 367 containing nickel element at a high concentration was removed. In this way, the state shown in FIG.

  In this state, the active layer (crystalline silicon film formed in an island shape) 366 has a concentration distribution in which the concentration of nickel element increases toward the surface of the crystalline silicon film. This state is due to nickel element gettering in the thermal oxide film 367 when the thermal oxide film 367 is formed. Therefore, after removing the thermal oxide film 367, it is useful to further etch the surface of the crystalline silicon film to remove the region having a high nickel element concentration.

The concentration of the nickel element remaining in the pattern 366 made of the lateral growth region thus obtained can be made lower than that shown in Example 50. This is also due to the fact that the concentration of the metal element contained in the lateral growth region is low in the first place. Thus, the nickel element concentration in the pattern 366 formed of the lateral growth region can be easily set to an order of 10 ¹⁷ cm ⁻³ or less.

  Further, when the thin film transistor is formed by utilizing the lateral growth region as in the present embodiment, the vertical growth region as shown in the embodiment 50 (in the case of the embodiment 50, the entire surface is vertically grown) is formed. A semiconductor device having higher mobility can be obtained as compared with the case where it is used. After obtaining the state shown in FIG. 46E, a thermal oxide film (not shown) was further formed on the surface of the active layer 366. The thermal oxide film can be formed to a thickness of 500 angstroms by performing a heat treatment for 30 minutes in an oxygen atmosphere at 950 ° C.

  Of course, the thickness of the thermal oxide film can be set to a desired and predetermined value by controlling the heating time, the heating temperature, and the oxygen concentration in the atmosphere. Thereafter, for example, when a thin film transistor is manufactured, a silicon oxide film is formed by plasma CVD or the like so as to cover the thermal oxide film, and a gate insulating film can be formed together with the thermal oxide film. . Further, the thermal oxide film may have a desired and predetermined film thickness and may be used as it is as a gate insulating film.

Example 53
Example 53 is an example in which a thin film transistor disposed in a pixel region of an active matrix liquid crystal display device or an active matrix EL display device is manufactured using the crystalline silicon film according to the present invention. FIG. 47 is a diagram showing a manufacturing process in this example.

  First, by the steps shown in Example 50 and Example 52, island-shaped semiconductor layers (layers made of a crystalline silicon film) patterned in the shape of an active layer were formed on a glass substrate, respectively. The following steps are the same for both. In the state shown in FIG. 47A, 369 is a glass substrate, 370 is a base film, and 371 is an active layer made of a crystalline silicon film.

  Next, before the thermal oxide film 368 was formed, plasma treatment was performed in a reduced pressure atmosphere in which oxygen and hydrogen were mixed. This plasma was generated by high frequency discharge. By this plasma treatment, organic substances present on the exposed surface of the active layer 371 were removed. Precisely, the organic substance adsorbed on the surface of the active layer is oxidized by the oxygen plasma, and the oxidized organic substance is reduced and vaporized by the hydrogen plasma.

  In this way, organic substances present on the exposed surface of the active layer 371 are removed. This removal of organic matter is very effective in suppressing the presence of fixed charges on the surface of the active layer 371. Fixed charges resulting from the presence of organic substances hinder the operation of the device and cause instability of characteristics, and it is very useful to reduce the presence thereof. Next, a thermal oxidation film 368 of 200 angstroms was formed on the surface by thermal oxidation, and the state shown in FIG. 47A was obtained.

Thereafter, a silicon oxynitride film 372 constituting a gate insulating film was formed to a thickness of 1000 angstroms. As a film forming method, a plasma CVD method using a mixed gas of oxygen, silane, and N ₂ O, a plasma CVD method using a mixed gas of TEOS and N ₂ O, and the like can be used. Here, TEOS and N ₂ are used. A mixed gas with ₂ O was used. This silicon oxynitride film 372 functions as a gate insulating film together with the thermal oxide film 368.

  When a metal element enters (penetrates) into the gate insulating film, the function as the insulating film is deteriorated, causing instability and variations in characteristics of the thin film transistor. In order to prevent them, the silicon oxynitride film It is effective to contain a halogen element. That is, by fixing the nickel element by the action of the halogen element, it is possible to prevent the function of the gate insulating film from being deteriorated due to the influence of the nickel element present in the active layer. In addition, the silicon oxynitride film has a significance that it is difficult for a metal element to enter the gate insulating film due to its dense film quality. Note that a commonly used silicon oxide film can also be used as the gate insulating film.

  After forming a silicon oxynitride film 372 functioning as a gate insulating film, an aluminum film (not shown) that functions as a gate electrode later was formed by a sputtering method. This aluminum film contained 0.2% by weight of scandium. The reason why scandium is contained in the aluminum film is to suppress generation of hillocks and whiskers in the subsequent process. Here, hillocks and whiskers mean that abnormal heating of aluminum occurs when heating is performed, and needle-like or stab-like protrusions are formed.

  After the aluminum film was formed, a dense anodic oxide film (not shown) was formed. This anodic oxide film was formed by using an ethylene glycol solution containing 3% by weight of tartaric acid as an electrolytic solution. That is, in this electrolytic solution, an anodic oxidation film having a dense film quality is formed on the surface of the aluminum film by performing anodization using the aluminum film as an anode and platinum as a cathode. The film thickness of the anodic oxide film having a dense film quality (not shown) is about 100 angstroms. This anodic oxide film has a role of improving adhesion with a resist mask to be formed later. The film thickness of the anodic oxide film can be controlled by the applied voltage during anodic oxidation.

  Next, a resist mask 374 was formed, and the aluminum film was patterned into a pattern indicated by 373. Thus, the state shown in FIG. 47B was obtained. Then, another anodic oxidation was performed. Here, a 3 wt% oxalic acid aqueous solution was used as the electrolytic solution. In this electrolytic solution, a porous anodic oxide film denoted by reference numeral 376 is formed by performing anodization using the aluminum pattern 373 as an anode.

  In this step, an anodic oxide film 376 is selectively formed on the side surface of the aluminum pattern because the resist mask 374 having high adhesion exists on the upper portion. This anodic oxide film can be grown to a thickness of several μm. Here, the film thickness was set to 6000 angstroms. The growth distance can be controlled by the anodic oxidation time.

  Next, after removing the resist mask 306, a dense anodic oxide film was formed again. That is, the anodic oxidation using the ethylene glycol solution containing 3% by weight of tartaric acid as an electrolytic solution was performed again. Then, an anodic oxide film having a dense film quality is formed as indicated by reference numeral 377 because the electrolyte solution enters the porous anodic oxide film 376.

  The dense anodic oxide film 377 has a thickness of 1000 angstroms. This film thickness was controlled by the applied voltage. Here, the exposed silicon oxynitride film 372 and the thermal oxide film 368 were etched. This etching utilized dry etching. Next, the porous anodic oxide film 376 was removed using a mixed acid obtained by mixing acetic acid, nitric acid and phosphoric acid. In this way, the state shown in FIG.

  Thereafter, impurity ions were implanted. Here, P (phosphorus) ions were implanted by plasma doping in order to fabricate an N-channel type thin film transistor. In this step, regions 379 and 383 that are heavily doped and regions 380 and 382 that are lightly doped are formed. This is because part of the remaining silicon oxide film 378 functions as a semi-transmissive mask, and part of the implanted ions is shielded there.

  Next, the region into which the impurity ions were implanted was activated by irradiating with ultraviolet rays. Infrared rays or laser light can be used instead of ultraviolet rays. Thus, the source region 379, the channel formation region 381, the drain region 383, and the low concentration impurity regions 380 and 382 are formed in a self-aligned manner. Here, what is indicated by reference numeral 382 is a region called an LDD (lightly doped drain) region.

  Note that when the thickness of the dense anodic oxide film 377 is increased to 2000 angstroms or more, an offset gate region can be formed outside the channel formation region 381 with the film thickness. In this embodiment, the offset gate region is formed, but since the size thereof is small, the contribution due to its existence is small, and the drawing becomes complicated, so it is not shown in the drawing.

  Next, a silicon oxide film, a silicon nitride film, or a stacked film thereof is formed as the interlayer insulating film 384. Here, a silicon oxide film is formed. The interlayer insulating film may be formed by forming a layer made of a resin material on a silicon oxide film or a silicon nitride film. Then, contact holes were formed, and a source electrode 385 and a drain electrode 386 were formed. Thus, the thin film transistor shown in FIG. 47E was completed.

Example 54
Example 54 is an example in which a thin film transistor was manufactured through a process different from that shown in Example 53 (FIG. 47). FIG. 48 shows a manufacturing process of this example. First, a crystalline silicon film was formed on a glass substrate by the steps shown in Example 50 or Example 52, respectively. Next, they were patterned, and further plasma treatment was performed in a mixed reduced pressure atmosphere of oxygen and hydrogen. The following steps are the same for both.

  Next, a thermal oxide film 387 was formed to a thickness of 200 angstroms to obtain the state shown in FIG. The thermal oxide film 387 was formed by performing a heat treatment for 30 minutes in an oxygen atmosphere at a temperature of 950 ° C. In the state shown in FIG. 48A, a portion indicated by reference numeral 388 is a glass substrate, 389 is a base film, and 390 is an active layer made of a crystalline silicon film. The thermal oxide film 387 is a thermal oxide film formed again after the removal of the thermal oxide film for gettering.

After obtaining the state shown in FIG. 48A, a silicon oxynitride film 391 constituting a gate insulating film was formed to a thickness of 1000 angstroms. This film formation was performed by a plasma CVD method using a mixed gas of oxygen, silane, and N ₂ O. Alternatively, a plasma CVD method using a mixed gas of TEOS and N ₂ O can be used. The silicon oxynitride film 391 forms a gate insulating film together with the thermal oxide film 387. Note that a silicon oxide film can be used instead of the silicon oxynitride film.

  Next, an aluminum film (not shown) that functions as a gate electrode later was formed by sputtering. This aluminum film contained 0.2% by weight of scandium. Thereafter, a dense anodic oxide film (not shown) was formed. This anodic oxide film was implemented by using an ethylene glycol solution containing 3% by weight of tartaric acid as an electrolytic solution. That is, in this electrolytic solution, an anodic oxidation film having a dense film quality was formed on the surface of the aluminum film by performing anodization using the aluminum film as an anode and platinum as a cathode.

  The film thickness of the anodic oxide film having a dense film quality (not shown) is about 100 angstroms. This anodic oxide film has a role of improving adhesion with a resist mask to be formed later. The film thickness of the anodic oxide film can be controlled by the applied voltage during anodic oxidation. Next, a resist mask 392 was formed, and the aluminum film was patterned into a pattern indicated by reference numeral 393.

  Next, anodic oxidation was performed again. Here, a 3 wt% oxalic acid aqueous solution was used as the electrolytic solution. In this electrolytic solution, a porous anodic oxide film denoted by reference numeral 394 is formed by performing anodization using the aluminum pattern 393 as an anode. In this step, an anodic oxide film 394 is selectively formed on the side surface of the aluminum pattern 393 because the resist mask 392 having high adhesion exists on the upper portion.

  The anodic oxide film can be grown to a thickness of several μm. Here, the film thickness was set to 6000 angstroms. The growth distance can be controlled by the anodic oxidation time. Next, after removing the resist mask 392, a dense anodic oxide film was formed again. That is, the anodic oxidation using the ethylene glycol solution containing 3% by weight of tartaric acid as an electrolytic solution was performed again. As a result, an anodic oxide film having a dense film quality was formed as indicated by reference numeral 395 because the electrolytic solution entered the porous anodic oxide film 394.

  Next, the first impurity ions were implanted. A source region 396 and a drain region 398 are formed by this impurity ion implantation. Note that impurity ions are not implanted into the region 397. Next, the porous anodic oxide film 394 was removed using a mixed acid solution in which acetic acid, nitric acid and phosphoric acid were mixed. Thus, the state shown in FIG. 48D was obtained. Thereafter, impurity ions were implanted again. This impurity ion was performed under the condition of light doping rather than the initial impurity ion implantation condition.

  Through the above steps, lightly doped regions indicated by reference numerals 399 and 400 were formed. A region denoted by reference numeral 401 is a channel formation region. Next, the region into which the impurity ions have been implanted is activated by irradiating with laser light or strong light. Here, the laser light irradiation is performed. Thus, the source region 396, the channel formation region 401, the drain region 398, and the low-concentration impurity regions 399 and 400 are formed in a self-aligned manner. Here, what is indicated by reference numeral 400 is a region called an LDD (lightly doped drain) region.

  Next, a silicon oxide film, a silicon nitride film, or a stacked film thereof is formed as the interlayer insulating film 402. Here, a silicon nitride film is formed. The interlayer insulating film may be formed by forming a layer made of a resin material on a silicon oxide film or a silicon nitride film. Next, contact holes were formed, and a source electrode 403 and a drain electrode 404 were formed. Thus, the thin film transistor shown in FIG. 48E was completed.

Example 55
The present embodiment 55 is an example in which an N channel type thin film transistor and a P channel type thin film transistor are configured in a complementary manner. The configuration shown in this embodiment can be used for various thin film integrated circuits integrated on an insulating surface, for example. For example, it can be used for a peripheral drive circuit of an active matrix liquid crystal display device. FIG. 49 is a diagram showing a manufacturing process of this example.

  First, as illustrated in FIG. 49A, a silicon oxide film or a silicon oxynitride film is formed as a base film 407 over a glass substrate 406. Although a silicon oxynitride film is preferably used, a silicon oxynitride film is formed here. Next, an amorphous silicon film (not shown) was formed by a plasma CVD method. Instead, a reduced pressure thermal CVD method may be used. Further, this amorphous silicon film was transformed into a crystalline silicon film by the method shown in Example 50.

  Next, after performing plasma treatment in a mixed atmosphere of oxygen and hydrogen, the obtained crystalline silicon film was patterned to form active layers 408 and 409. Thus, the state shown in FIG. Here, in order to suppress the influence of carriers moving on the side surface of the active layer, in the state shown in FIG. 49A, the temperature is 650 ° C. for 10 hours in a nitrogen atmosphere containing 3% by volume of HCl. Heat treatment was performed.

  If the trap level due to the presence of the metal element is present on the side surfaces of the active layers 408 and 409, the OFF current characteristics are deteriorated. Therefore, the above processing is performed to reduce the level density on the side surfaces of the active layer. It is useful to leave. Next, a thermal oxide film 405 and a silicon oxynitride film 410 constituting a gate insulating film were formed. Here, when quartz is used as the substrate, it is desirable to form the gate insulating film only by the thermal oxide film formed by the above-described thermal oxidation method.

  Next, an aluminum film (not shown) for forming a gate electrode later was formed to a thickness of 4000 angstroms. As the metal other than the aluminum film, an anodizable metal (for example, tantalum) can be used. After forming the aluminum film, an extremely thin dense anodic oxide film was formed on the surface by the method described above. Next, a resist mask (not shown) was placed on the aluminum film, and the aluminum film was patterned. Then, anodization was performed using the obtained aluminum pattern as an anode, and porous anodic oxide films 413 and 414 were formed. The thickness of the porous anodic oxide film was 5000 angstroms.

  Furthermore, anodization was performed again under the conditions for forming a dense anodic oxide film, and dense anodic oxide films 415 and 416 were formed. Here, the dense anodic oxide films 415 and 416 have a thickness of 800 angstroms. Thus, the state shown in FIG. 49B was obtained. Further, the exposed silicon oxide film 410 and the thermal oxide film 405 were removed by dry etching to obtain the state shown in FIG. Thereafter, the porous anodic oxide films 413 and 414 were removed using a mixed acid obtained by mixing acetic acid, nitric acid and phosphoric acid. Thus, the state shown in FIG.

  Here, resist masks are alternately arranged so that P (phosphorus) ions are implanted into the left thin film transistor and B (boron) ions are implanted into the right thin film transistor. By the implantation of impurity ions (P ions), a source region 419 and a drain region 422 having a high concentration N-type were formed in a self-aligned manner. In addition, a weak N-type region 420 doped with P ions at a low concentration was formed at the same time, and a channel formation region 421 was formed at the same time.

  The reason why the weak N-type region indicated by reference numeral 420 is formed is that the remaining gate insulating film 417 exists. That is, P ions that have passed through the gate insulating film 417 are partially shielded by the gate insulating film 417. Further, the source region 426 and the drain region 423 having strong P-type are formed in a self-aligned manner by the same principle and method. Further, a low concentration impurity region 425 is formed at the same time, and a channel formation region 424 is formed at the same time.

  If the dense anodic oxide films 415 and 416 are as thick as 2000 angstroms, the offset gate region can be formed in contact with the channel formation region with that thickness. In the case of this embodiment, since the dense anodic oxide films 415 and 416 are as thin as 1000 angstroms or less, their presence can be ignored. Next, laser light was irradiated to anneal the region into which impurity ions were implanted. Note that strong light can be used instead of laser light.

  Next, as shown in FIG. 49E, a silicon nitride film 427 and a silicon oxide film 428 were formed as interlayer insulating films. The thickness of each film was 1000 angstroms. Note that the silicon oxide film 428 is not necessarily formed. Thus, the thin film transistor is covered with the silicon nitride film. Since the silicon nitride film is dense and has good interface characteristics, the reliability of the thin film transistor can be improved with such a structure.

  Further, an interlayer insulating film 429 made of a resin material was formed using a spin coating method. Here, the thickness of the interlayer insulating film 429 is 1 μm. Then, contact holes were formed to form the source electrode 430 and the drain electrode 431 of the left N-channel thin film transistor, and at the same time, the source electrode 432 and the drain electrode 431 of the right thin film transistor were formed. Here, the drain electrodes 431 are arranged in common. In this manner, a thin film transistor in which the N-channel thin film transistor and the P-channel thin film transistor shown in FIG.

  As described above, a thin film transistor circuit having a complementary CMOS structure can be formed. In the structure shown in this embodiment, a structure in which the thin film transistor is covered with a silicon nitride film and further covered with a resin material can be obtained. With this configuration, it is possible to make the movable ion and moisture highly resistant to intrusion. Further, when a multilayer wiring is formed, it is possible to prevent a capacitance from being formed between the thin film transistor and the wiring.

Example 56
The present embodiment 56 is an example in which nickel element is directly introduced into the surface of the base film in the step shown in the embodiment 50. In this case, the nickel element is held in contact with the lower surface of the amorphous silicon film. In this case, nickel element is introduced after the formation of the base film, and the nickel element (the metal element) is first held in contact with the surface of the base film.

  In this embodiment, nickel element is directly introduced by applying an aqueous solution of nickel acetate to the surface of the base film, and the other steps are the same as in Embodiment 50, as shown in FIG. In addition, an island-shaped pattern 356 made of a crystalline silicon film with a reduced nickel content was obtained. As a method for introducing nickel element, in addition to a method using a solution, a sputtering method, a CVD method, an adsorption method, or the like can be used.

Example 57
The present embodiment 57 is irradiated with laser light in the state of FIG. 45 (E), the state of FIG. 46 (E), the state of FIG. 47 (A) and the state of FIG. 48 (A) corresponding to each of the above embodiments. This is an example in which the crystallinity of the island-shaped pattern made of the crystalline silicon film obtained is improved. In this embodiment, laser light was irradiated in each of these states to improve the crystallinity of the island-shaped pattern made of the crystalline silicon film.

  45E, 46E, 47A, and 48A, in the case of irradiating laser light, annealing is performed on the entire film before patterning. As compared with the above, a predetermined annealing effect can be obtained with a relatively low irradiation energy density. This is considered to be because the energy efficiency used for annealing increases because the laser energy is irradiated to a small area.

Example 58
Example 58 is an example in which a crystalline silicon film is obtained on a glass substrate using nickel element. In this example, first, a crystalline silicon film having high crystallinity was obtained by the action of nickel element. Laser irradiation was then performed. By irradiating this laser light, the crystallinity of the film is enhanced and nickel elements present locally are diffused in the film. That is, the mass of nickel was reduced or eliminated.

  Next, an oxide film containing F (fluorine) was formed on the crystalline silicon film by a thermal oxidation method. At this time, the nickel element remaining in the obtained crystalline silicon film is gettered into the thermal oxide film by the action of the F element. In this case, since the nickel element is dispersed by the previous laser beam irradiation, gettering proceeds effectively. Further, the thermal oxide film containing nickel element at a high concentration was removed by gettering as described above. By doing so, a crystalline silicon film having a high crystallinity on the glass substrate and a low nickel element concentration was obtained.

  FIG. 50 is a diagram showing a manufacturing process of this example. First, a silicon oxide film 434 having a thickness of 3000 angstroms was formed on a Corning 1737 glass substrate (strain point 667 ° C.) 433 as a base film. A sputtering method was used for this film formation. The silicon oxide film 434 has a function of preventing diffusion of impurities from the glass substrate in a later step. It also has a function of relieving stress acting between the glass substrate and a silicon film to be formed later.

  It is effective to contain a trace amount of halogen element in the base film 434. In this manner, in a later step, a metal element that promotes crystallization of silicon existing in the semiconductor layer can be gettered into the base film with a halogen element. It is also effective to add a hydrogen plasma treatment after forming the base film. This is because the carbide existing on the surface of the base film is removed, and there is an effect of suppressing the existence of fixed charge levels at the interface with the silicon film to be formed later. As an alternative to hydrogen plasma treatment, it is also effective to perform plasma treatment in an atmosphere in which oxygen and hydrogen are mixed.

Next, an amorphous silicon film 435 to be a crystalline silicon film later was formed to a thickness of 500 angstrom by a low pressure thermal CVD method. The reason why the low pressure thermal CVD method is used is that the crystalline silicon film obtained later is superior in film quality, specifically, the film quality is dense. As a method other than the low pressure thermal CVD method, a plasma CVD method can be used. The amorphous silicon film produced here preferably has an oxygen concentration in the film of 5 × 10 ¹⁷ cm ⁻³ to 2 × 10 ¹⁹ cm ⁻³ .

This is because oxygen plays an important role in a process of gettering a metal element (a metal element that promotes crystallization of silicon) later (in this embodiment, a nickel gettering process). However, when the oxygen concentration is higher than the above concentration range, care must be taken because crystallization of the amorphous silicon film is inhibited. Further, when the oxygen concentration is lower than the above concentration range, the contribution of the metal element to the gettering action is reduced. Also, other impurity concentrations, such as nitrogen and carbon impurity concentrations, should be as low as possible. Specifically, the concentration is preferably 2 × 10 ¹⁹ cm ⁻³ or less.

  The upper limit of the thickness of the amorphous silicon film is about 2000 angstroms. This is because it is disadvantageous that the film is too thick in order to obtain the effect of subsequent laser light irradiation. The disadvantage of the thick film is that most of the laser light applied to the silicon film is absorbed on the surface of the film. Note that the lower limit of the film thickness of the amorphous silicon film 435 is practically about 200 angstroms although it depends on the film forming method. If the thickness is less than that, a problem arises in the uniformity of the thickness.

  Next, a metal element for crystallizing the amorphous silicon film 435 was introduced. Here, a nickel element is used as a metal element for promoting crystallization of silicon, and a method using a solution is used as a method for introducing the nickel element. Here, nickel element was introduced by applying a nickel acetate aqueous solution containing 10 ppm (weight) of nickel to the surface of the amorphous silicon film 435. As a method for introducing nickel element, in addition to the method using the above solution, a sputtering method, a CVD method, a plasma treatment or an adsorption method can be used. Among these, the method using a solution is useful in that it is simple and the concentration of the metal element can be easily adjusted.

  By applying the nickel acetate aqueous solution, a water film of the nickel acetate aqueous solution indicated by 436 in FIG. 50 (A) was formed. After obtaining this state, excess solution was blown off using a spinner (not shown). In this way, nickel was held in contact with the surface of the amorphous silicon film 435. The amount of nickel element introduced into the amorphous silicon film 435 can also be adjusted by the retention time of the water film 436 and the removal conditions using a spinner.

  In view of residual impurities in the subsequent heating step, it is preferable to use, for example, nickel sulfate instead of the nickel acetate aqueous solution. This is because the nickel acetate salt solution contains carbon, which may be carbonized in a subsequent heating step and carbon components may remain in the film or on the surface of the film.

  Next, in the state shown in FIG. 50B, heat treatment was performed to crystallize the amorphous silicon film 435, so that a crystalline silicon film 437 was obtained. Here, heat treatment was performed in a nitrogen atmosphere at 640 ° C. containing 3% by volume of hydrogen, and the heating time was 4 hours. The heat treatment can be performed at a temperature in the range of 500 to 700 ° C., but is preferably performed at a temperature below the strain point of the glass substrate. Since the strain point of the Corning 1737 glass substrate used in this example is 667 ° C., the upper limit is preferably about 650 ° C. with a margin.

The reason why the atmosphere is reduced in the crystallization process by the heat treatment is to prevent oxides from being formed during the heat treatment process. More specifically, the reaction with nickel and oxygen, because the NiO _X is prevented from undesirably formed on the surface of the film or within the film. Oxygen combines with nickel in a later gettering step and contributes greatly to nickel gettering. However, it has been found that the combination of oxygen and nickel at this crystallization stage inhibits crystallization. Therefore, in the crystallization process by heating, it is important to suppress the formation of oxide as much as possible.

  In addition, the oxygen concentration in the atmosphere in which the heat treatment for crystallization is performed needs to be on the order of ppm, preferably 1 ppm or less. As a gas occupying most of the atmosphere in which the heat treatment for crystallization is performed, an inert gas such as argon or a mixed gas thereof can be used in addition to nitrogen. After the crystallization step by the heat treatment, nickel element remains as a certain amount of solid. This was confirmed by observation with a TEM (transmission electron microscope). The cause of the fact that nickel is present in a certain amount of mass is not clear, but it is thought to be related to some crystallization mechanism.

  Next, as shown in FIG. 50C), laser light was irradiated. Here, a method of using a KrF excimer laser (wavelength 248 nm) and irradiating while scanning a linear laser beam shape was adopted. By this laser light irradiation, nickel elements that have been locally concentrated as a result of the crystallization by the heat treatment described above are dispersed in the film 437 to some extent. That is, the nickel element mass can be eliminated or reduced, and the nickel element can be dispersed. As the laser light, an XeCl excimer laser (wavelength 308 nm) or other types of excimer lasers can be used. Moreover, it is good also as a structure which irradiates with an ultraviolet-ray and infrared rays instead of a laser beam.

Next, heat treatment was performed again in the process illustrated in FIG. This heat treatment is a treatment for forming a thermal oxide film for gettering nickel element. Here, the atmosphere is an oxygen atmosphere containing ₃ % by volume of hydrogen and 100 ppm (capacity) of ClF _3. Then, a heat treatment at a temperature of 640 ° C. was performed. In this step, a thermal oxide film was formed to a thickness of 200 angstroms.

  This step is a step for removing nickel element intentionally mixed in the initial stage for crystallization from the crystalline silicon film 437. This heat treatment is performed in a temperature range of about 500 to 700 ° C. when the substrate is an ordinary glass substrate. The upper limit of the heat treatment temperature is limited by the strain point of the glass substrate to be used, and care should be taken because the substrate is deformed when the heat treatment is performed at a temperature equal to or higher than the strain point of the glass substrate to be used.

  In this step, the nickel element dispersed by the laser beam irradiation is gettered into the oxide film 438 to be formed. Therefore, the nickel concentration in oxide film 438 is naturally higher than that in other regions. Further, a tendency for nickel element to increase in the vicinity of the interface between the crystalline silicon film 437 and the thermal oxide film 438 was observed. This is considered to be because the region where gettering is mainly performed is on the oxide film side in the vicinity of the interface between the silicon film and the oxide film.

In addition, it is considered that the gettering progresses in the vicinity of the interface due to the presence of stress and defects in the vicinity of the interface. Moreover, the tendency for the concentration of fluorine and chlorine to increase near the interface between the silicon film 437 and the thermal oxide film 438 was observed. The crystalline silicon film thus obtained contains a metal element that promotes crystallization of silicon at a concentration of 1 × 10 ¹⁶ cm ^{−3 to} 5 × 10 ¹⁸ cm ⁻³ and contains 1 × 10 fluorine atoms. It is contained at a concentration of ¹⁵ cm ⁻³ to 1 × 10 ²⁰ cm ⁻³ , and hydrogen atoms are contained at a concentration of 1 × 10 ¹⁷ cm ⁻³ to 1 × 10 ²¹ cm ⁻³ .

  After the formation of the thermal oxide film 438 shown in FIG. 50D, the oxide film 438 containing nickel at a high concentration was removed. The oxide film 438 can be removed by wet etching using buffer hydrofluoric acid (other hydrofluoric acid-based etchants) or dry etching. Here, wet etching using buffer hydrofluoric acid was performed. Thus, as shown in FIG. 50E, a crystalline silicon film 439 with a reduced concentration of nickel was obtained.

  In the vicinity of the surface of the obtained crystalline silicon film 439, since a relatively high concentration of nickel element is contained, the etching of the oxide film 438 is further advanced to slightly over-etch the surface of the crystalline silicon film 439. It is effective. It is also effective to further promote the crystallinity of the obtained crystalline silicon film 439 by removing the thermal oxide film 438 and irradiating the laser beam again.

Example 59
Example 59 is an example in which Cu is used as the metal element for promoting crystallization of silicon in the configuration shown in Example 58. In this case, cupric acetate [Cu (CH ₃ COO) ₂ ], cupric chloride (CuCl ₂ 2H ₂ O), or the like is used as a solution for introducing Cu. A CuCl ₂ 2H ₂ O) aqueous solution was used. Other steps were the same as those shown in Example 58, and the state shown in FIG.

Example 60
The present Example 60 is an example in which crystal growth in a form different from that of the Example 58 is performed. This embodiment relates to a method of performing crystal growth in a direction parallel to the substrate, called lateral growth, using a metal element that promotes crystallization of silicon. FIG. 51 shows a manufacturing process of this example.

  First, a silicon oxide film having a thickness of 3000 angstroms was formed as a base film 441 on a Corning 1737 glass substrate 440. Next, an amorphous silicon film 442 serving as a starting film for the crystalline silicon film was formed to a thickness of 600 angstrom by low pressure thermal CVD. As described above, the thickness of the amorphous silicon film is preferably 2000 angstroms or less. Another substrate such as a quartz substrate may be used as the substrate.

  Next, a silicon oxide film (not shown) was formed to a thickness of 1500 angstroms and patterned to form a mask indicated by reference numeral 443. This mask has an opening formed in a region indicated by reference numeral 444. In the region where the opening 444 is formed, the amorphous silicon film 442 is exposed. The opening 444 has an elongated rectangular shape in the longitudinal direction from the depth of the drawing toward the front. The width of the opening 444 is suitably 20 μm or more, and the length in the longitudinal direction may be formed with a required length. In this example, the width was 50 μm and the length was 8 cm.

  And as shown in Example 58, after applying nickel acetate aqueous solution containing 10 ppm of nickel element in terms of weight, spin drying was performed using a spinner to remove excess solution. Thus, a state in which the nickel element was held in contact with the exposed surface of the amorphous silicon film 442 was realized as indicated by a dotted line 445 in FIG.

  Next, heat treatment was performed at a temperature of 640 ° C. for 4 hours in a nitrogen atmosphere containing 3% by volume of hydrogen and containing as little oxygen as possible. Then, crystal growth progressed in a direction parallel to the substrate 440 as indicated by 446 in FIG. This crystal growth proceeds from the region of the opening 444 into which nickel element is introduced toward the periphery. Such crystal growth in a direction parallel to the substrate is referred to as lateral growth or lateral growth in this specification.

  Under the conditions as shown in this embodiment, this lateral growth can be performed over 100 μm or more. Thus, a silicon film 447 having a laterally grown region was obtained. In the region where the opening 444 is formed, crystal growth in the vertical direction called vertical growth proceeds from the surface of the silicon film toward the base interface. Next, the mask 443 made of a silicon oxide film for selectively introducing nickel element was removed. In this way, the state shown in FIG. In this state, the crystalline silicon film 447 includes a vertical growth region, a lateral growth region, and a region where the crystal growth does not reach (amorphous state).

  In this state, nickel element is unevenly distributed in the film. In particular, the nickel element is present at a relatively high concentration in the region where the opening 444 was formed and the tip portion of the crystal growth indicated by reference numeral 446. Next, laser light was irradiated. Here, a KrF excimer laser was used as in Example 58. By this step, the unevenly distributed nickel element is diffused, and a state in which gettering can be easily performed in the subsequent gettering step is obtained.

After completion of the laser light irradiation, heat treatment was performed at a temperature of 650 ° C. in an atmosphere containing ₃ % by volume of hydrogen and 100 ppm (volume) of NF ₃ . In this step, an oxide film 448 containing nickel element at a high concentration was formed to a thickness of 200 angstroms, and at the same time, the nickel element concentration in the silicon film 447 was relatively reduced. After the formation of the thermal oxide film by the heat treatment, the thermal oxide film 448 containing nickel element at a high concentration was removed.

  It is effective to further etch the surface of the crystalline silicon film after removing the thermal oxide film 448. Next, patterning was performed to form a pattern 449 composed of a laterally grown region. The concentration of the nickel element remaining in the pattern 449 composed of the lateral growth region obtained in this way can be made lower than that in the case of the embodiment 58.

This is also due to the fact that the concentration of the metal element contained in the lateral growth region is low in the first place. Specifically, the concentration of the nickel element in the pattern 448 composed of the lateral growth region can be easily set to an order of 10 ¹⁷ cm ⁻³ or less. In addition, after forming the pattern shown in FIG. 51E, it is useful to further perform an etching process to remove the nickel element existing on the pattern surface.

  Next, a thermal oxide film 450 was formed on the formed pattern 449. The thermal oxide film was formed to a thickness of 200 angstroms by performing a heat treatment in an oxygen atmosphere at a temperature of 650 ° C. for 12 hours. Further, it is effective to include fluorine in the atmosphere when forming the thermal oxide film 450. When the thermal oxide film 450 is formed, if fluorine is contained in the atmosphere, the action of fluorine can fix the nickel element and neutralize dangling bonds on the surface of the silicon film. That is, the interface characteristics between the active layer and the gate insulating film can be improved.

  Further, chlorine may be used instead of fluorine. If this thermal oxide film constitutes a thin film transistor, it will become a part of the gate insulating film later. After that, when a thin film transistor is manufactured, a silicon oxide film is formed by plasma CVD or the like to cover the thermal oxide film 450, and a gate insulating film is formed.

Example 61
Embodiment 61 is an example in which a thin film transistor disposed in a pixel region of an active matrix liquid crystal display device or an active matrix EL display device is manufactured using the crystalline silicon film obtained according to the present invention. .

  FIG. 52 shows a manufacturing process of this example. First, a crystalline silicon film was formed on a glass substrate by the steps shown in Example 58 and Example 60, respectively. The following steps are the same for both. When a crystalline silicon film is obtained with the structure shown in Embodiment 58, the state shown in FIG. 52 (A) is obtained by performing patterning of the silicon silicon film and passing through the steps shown in FIGS. Got.

  In the state shown in FIG. 52A, reference numeral 452 denotes a glass substrate, 453 denotes a base film, and 454 denotes an active layer made of a crystalline silicon film. After obtaining the state shown in FIG. 52A, plasma treatment was performed in a reduced pressure atmosphere in which oxygen and hydrogen were mixed. This plasma was generated by high frequency discharge. By this plasma treatment, organic substances present on the exposed surface of the active layer 454 were removed. Precisely, the organic substance adsorbed on the surface of the active layer is oxidized by the oxygen plasma, and the oxidized organic substance is further reduced and vaporized by the hydrogen plasma. In this way, organic substances present on the exposed surface of the active layer 454 were removed.

  The removal of the organic substance is very effective in reducing the presence of fixed charges on the surface of the active layer 454. Fixed charges resulting from the presence of organic substances hinder the operation of the device and cause instability of characteristics, and it is very useful to reduce the presence thereof. After removing the organic material in this manner, thermal oxidation was performed in an oxygen atmosphere at a temperature of 640 ° C. to form a thermal oxide film 451 having a thickness of 100 Å. This thermal oxide film has high interface characteristics with the semiconductor layer, and will later constitute a part of the gate insulating film. In this way, the state shown in FIG.

  Thereafter, a silicon oxide film 455 constituting a gate insulating film was formed to a thickness of 1000 angstroms. The silicon oxide film 455 was formed by a plasma CVD method. This silicon oxide film 455 functions as a gate insulating film together with the thermal oxide film 451. Note that it is effective to include a halogen element in the silicon oxide film 455. In this case, the nickel element can be immobilized by the action of the halogen element. Further, it is possible to suppress the deterioration of the function of the gate insulating film as an insulating film due to the influence of nickel element existing in the active layer (the same applies to other metal elements that promote crystallization of silicon). it can.

  Next, an aluminum film (not shown) that functions as a gate electrode later was formed by sputtering. This aluminum film contained 0.2% by weight of scandium. The reason why scandium is contained in the aluminum film is to suppress generation of hillocks and whiskers in the subsequent process. Here, hillocks and whiskers mean needle-like or stab-like protrusions resulting from abnormal growth of aluminum during heating.

  After the aluminum film was formed as described above, a dense anodic oxide film (not shown) was formed. This anodic oxide film was formed using an electrolytic solution of an ethylene glycol solution containing 3% by weight of tartaric acid, an aluminum film as an anode, and platinum as a cathode. In this step, an anodic oxide film having a dense film quality was formed to a thickness of 100 angstroms on the aluminum film. This anodic oxide film has a role of improving adhesion with a resist mask to be formed later. The thickness of the anodic oxide film was controlled by the applied voltage during anodic oxidation.

  Next, a resist mask 457 was formed, and the aluminum film was patterned into a pattern indicated by 456. In this way, the state shown in FIG. 52 (B) was obtained. Here, anodic oxidation was performed again. Here, a 3 wt% oxalic acid aqueous solution was used as the electrolytic solution. In this electrolytic solution, anodization was performed using the aluminum pattern 456 as an anode, whereby a porous anodic oxide film indicated by reference numeral 459 was formed.

  In this step, an anodic oxide film 459 is selectively formed on the side surface of the aluminum pattern 456 because the resist mask 457 with high adhesion exists on the upper portion. This anodic oxide film 459 can be grown to a thickness of several μm. Here, the film thickness was set to 6000 angstroms. The growth distance can be controlled by the anodic oxidation time.

  Next, after removing the resist mask 457, a dense anodic oxide film was formed again. That is, the anodic oxidation was again performed using the above-described ethylene glycol solution containing 3% by weight of tartaric acid as an electrolytic solution. In this step, an anodic oxide film having a dense film quality was formed as indicated by reference numeral 460 because the electrolyte solution entered (invaded) into the porous anodic oxide film 459.

  The film thickness of the dense anodic oxide film 460 was 1000 angstroms, but the film thickness was controlled by the applied voltage. Next, the exposed silicon oxide film 455 was etched, and at the same time, the thermal oxide film 451 was etched. Dry etching was used for this etching. Then, the porous anodic oxide film 459 was removed using a mixed acid obtained by mixing acetic acid, nitric acid and phosphoric acid. In this way, the state shown in FIG.

  Thereafter, impurity ions were implanted. Here, in order to fabricate an N-channel type thin film transistor, P (phosphorus) ions were implanted by a plasma doping method. In this step, regions 462 and 466 that are heavily doped and regions 463 and 465 that are lightly doped are formed. This is because the remaining silicon oxide film 461 functions as a semi-transmissive mask, and a part of the implanted ions is shielded there.

  Next, the region into which the impurity ions were implanted was activated by laser light irradiation. Instead of this laser light, strong light can be applied. Thus, the source region 462, the channel formation region 464, the drain region 466, and the low-concentration impurity regions 463 and 465 are formed in a self-aligned manner. Here, a region denoted by reference numeral 465 is a region called an LDD (lightly doped drain) region.

  When the thickness of the dense anodic oxide film 460 is increased to 2000 angstroms or more, an offset gate region can be formed outside the channel formation region 464 with the film thickness. In this embodiment, the offset gate region is formed, but since the size thereof is small, the contribution due to its existence is small, and the drawing becomes complicated, so it is not shown in the drawing. It should be noted that an anodic oxide film having a dense film quality is formed as thick as 2000 angstroms or more because an applied voltage of 200 V or more is required.

  Next, a silicon oxide film, a silicon nitride film, or a stacked film thereof is formed as the interlayer insulating film 467. Here, the stacked film is formed. As the interlayer insulating film, a layer made of a resin material may be used on the silicon oxide film or the silicon nitride film. Then, contact holes were formed, and a source electrode 468 and a drain electrode 469 were formed. Thus, a thin film transistor shown in FIG. 52E was obtained.

Example 62
Example 62 is an example in which a thin film transistor was manufactured by a process different from the process shown in Example 61 (FIG. 52). FIG. 53 shows a manufacturing process of this example. First, a crystalline silicon film was formed on a glass substrate by the steps shown in Example 58 and Example 60, respectively. And the state shown to FIG. 53 (A) was obtained by patterning it. The following steps are the same for both.

  After obtaining the state shown in FIG. 53A, plasma treatment was performed in a mixed reduced pressure atmosphere of oxygen and hydrogen. In the state shown in FIG. 53A, 471 is a glass substrate, 472 is a base film made of a silicon oxide film, and reference numeral 473 is an active layer made of a crystalline silicon film. Reference numeral 470 denotes a thermal oxide film formed again after removing the thermal oxide film for gettering. Next, as shown in FIG. 53B, a silicon oxide film 474 constituting a gate insulating film was formed to a thickness of 1000 angstroms by plasma CVD.

  The silicon oxide film 474 and the thermal oxide film 470 constitute a gate insulating film. Next, an aluminum film (not shown) that functions as a gate electrode later was formed by sputtering. This aluminum film contained 0.2% by weight of scandium. After the aluminum film was formed, a dense anodic oxide film (not shown) was formed on the surface. This anodic oxide film was implemented by using an ethylene glycol solution containing 3% by weight of tartaric acid as an electrolytic solution.

  The film thickness of the anodic oxide film having a dense film quality (not shown) is about 100 angstroms. This anodic oxide film has a role of improving adhesion with a resist mask to be formed later. The film thickness of the anodic oxide film can be controlled by the applied voltage during anodic oxidation. Next, a resist mask 475 was formed. The aluminum film was patterned into a pattern indicated by reference numeral 476.

  Then, another anodic oxidation was performed. Here, a 3 wt% oxalic acid aqueous solution was used as the electrolytic solution. In this electrolytic solution, a porous anodic oxide film indicated by reference numeral 477 was formed by performing anodization using the aluminum pattern 476 as an anode. In this step, an anodic oxide film 477 is selectively formed on the side surface of the aluminum pattern 476 because the resist mask 475 having high adhesion exists on the upper portion.

  The anodic oxide film can be grown to a thickness of several μm. Here, the film thickness was set to 6000 angstroms. The growth distance can be controlled by the anodic oxidation time. Next, after removing the resist mask 475, a dense anodic oxide film was formed again. That is, the anodic oxidation using the ethylene glycol solution containing 3% by weight of tartaric acid as an electrolytic solution was performed again. As a result, an anodic oxide film having a dense film quality is formed as indicated by reference numeral 478 because the electrolytic solution enters (invades) into the porous anodic oxide film 477.

  Next, the first impurity ions were implanted. Here, in order to fabricate an N-channel thin film transistor, P (phosphorus) ions were implanted. Note that if a p-channel thin film transistor is manufactured, B (boron) ions are implanted. By this impurity ion implantation, a source region 479 and a drain region 481 are formed. At this time, impurity ions are not implanted into the region indicated by reference numeral 480. Next, the porous anodic oxide film 477 was removed using a mixed acid obtained by mixing acetic acid, nitric acid, and phosphoric acid. In this way, the state shown in FIG. 53 (D) was obtained.

  Thereafter, impurity ions (phosphorus ions) were implanted again. This impurity ion was performed under the condition of light doping (low dose amount) than the initial impurity ion implantation condition. In this step, lightly doped regions 482 and 483 are formed, and a region indicated by reference numeral 484 becomes a channel forming region.

  Next, the region into which the impurity ions were implanted was activated by laser light irradiation. Note that strong light such as infrared rays or ultraviolet rays may be irradiated instead of the laser light. Thus, the source region 479, the channel formation region 484, the drain region 481, and the low concentration impurity regions 482 and 483 are formed in a self-aligned manner. Here, what is indicated by reference numeral 483 is a region referred to as an LDD (lightly doped drain) region.

  Next, a silicon oxide film, a silicon nitride film, or a stacked film thereof is formed as the interlayer insulating film 485. Here, a silicon nitride film is used. As the interlayer insulating film, a silicon oxide film or a silicon nitride film formed with a layer made of a resin material may be used. Then, contact holes were formed, a source electrode 486 and a drain electrode 487 were formed, and a heat treatment (hydrogenation heat treatment) for 1 hour was performed in a hydrogen atmosphere at a temperature of 350 ° C. In this step, defects and dangling bonds in the active layer are neutralized. Thus, a thin film transistor shown in FIG. 53E was obtained.

Example 63
Example 63 is an example in which an N-channel thin film transistor and a P-channel thin film transistor are configured to be complementary. The configuration shown in this embodiment can be used for various thin film integrated circuits integrated on an insulating surface, for example. For example, it can be used for a peripheral drive circuit of an active matrix liquid crystal display device. FIG. 54 is a diagram showing a process of this example.

  First, as shown in FIG. 54A, a silicon oxide film was formed as a base film 490 over a glass substrate 489. Note that a silicon nitride film may be used instead of the silicon oxide film. Next, an amorphous silicon film (not shown) is formed by a plasma CVD method or a low pressure thermal CVD method. Here, the former is used. Further, this amorphous silicon film was transformed into a crystalline silicon film by the method shown in Example 58. Then, after plasma treatment in a mixed atmosphere of oxygen and hydrogen, the crystalline silicon film was patterned to obtain active layers 491 and 492. Thereafter, a thermal oxide film indicated by reference numeral 488 was formed. The film thickness of the thermal oxide film 488 was about 100 angstroms. In this way, the state shown in FIG. 54 (A) was obtained.

  Next, a silicon oxide film was formed as the gate insulating film 493. Then, an aluminum film (not shown) for forming a gate electrode later was formed to a thickness of 4000 angstrom by sputtering. As the metal other than the aluminum film, an anodizable metal (for example, tantalum) can be used. After forming the aluminum film, an extremely thin dense anodic oxide film (not shown) was formed on the surface by the method described above.

  Next, a resist mask (not shown) was placed on the aluminum film, and the aluminum film was patterned. Then, anodization was performed using the obtained aluminum pattern as an anode, and porous anodic oxide films 496 and 497 were formed. The thickness of the porous anodic oxide film was 5000 angstroms. Next, the resist mask (not shown) was removed, and anodization was performed again under the conditions for forming a dense anodized film again. Dense anodic oxide films 498 and 499 were formed by this process.

  Here, the dense anodic oxide films 498 and 499 have a thickness of 800 angstroms. In this way, the state shown in FIG. 54 (B) was obtained. Further, the exposed silicon oxide film 493 and the thermal oxide film 488 were removed by dry etching to obtain the state shown in FIG. Thereafter, the porous anodic oxide films 496 and 497 were removed using a mixed acid obtained by mixing acetic acid, nitric acid and phosphoric acid. In this way, the state shown in FIG. 54 (D) was obtained.

  Here, resist masks were alternately arranged so that P (phosphorus) ions were implanted into the left thin film transistor and B (boron) ions were implanted into the right thin film transistor, and these were implanted by plasma doping. By the implantation of the impurity ions, a source region 502 and a drain region 505 having a high concentration N type are formed in a self-aligned manner. At the same time, a weak N-type region 503 doped with P ions at a low concentration was formed, and a channel formation region 504 was formed at the same time.

  Here, the reason why the weak N-type region indicated by reference numeral 503 is formed is that the remaining gate insulating film 500 exists. That is, P ions that have passed through the gate insulating film 500 are partially shielded by the gate insulating film 500. Further, the source region 509 and the drain region 506 having strong P-type were formed in a self-aligned manner by the same principle and method. At the same time, a low concentration impurity region 508 and a channel formation region 507 were formed at the same time.

  When the dense anodic oxide films 498 and 499 are as thick as 2000 angstroms, the offset gate region can be formed in contact with the channel formation region with that thickness. In the case of the present embodiment, since the dense anodic oxide films 498 and 499 are as thin as 1000 angstroms or less, their presence can be ignored.

  Next, laser light was irradiated to anneal the region into which impurity ions were implanted. Note that strong light such as ultraviolet rays may be irradiated instead of laser light. Then, as shown in FIG. 54E, a silicon nitride film 510 and a silicon oxide film 511 were formed as interlayer insulating films, and the respective film thicknesses were set to 1000 angstroms. Note that the silicon oxide film 511 is not necessarily formed. Here, the thin film transistor is covered with the silicon nitride film. Since the silicon nitride film is dense and has good interface characteristics, the reliability of the thin film transistor can be improved with such a structure.

  Further, an interlayer insulating film 512 made of a resin material was formed using a spin coat method. Here, the thickness of the interlayer insulating film 512 is 1 μm. Then, contact holes were formed, and a source electrode 513 and a drain electrode 514 of the left N-channel thin film transistor were formed. At the same time, a source electrode 515 and a drain electrode 514 of the right thin film transistor were formed. Here, the drain electrode 514 is disposed in common.

  Thus, a thin film transistor circuit having a complementary CMOS structure shown in FIG. 54 (F) was formed. In the structure shown in this embodiment, a structure in which the thin film transistor is covered with a silicon nitride film and further covered with a resin material can be obtained. With this configuration, it is possible to achieve high durability in which mobile ions and moisture hardly enter. Further, when a multilayer wiring is formed, it is possible to prevent a capacitance from being formed between the thin film transistor and the wiring.

<< Example 64 >>
Example 64 is an example in which nickel element was directly introduced into the surface of the base film in the step shown in Example 58. In this case, the nickel element is held in contact with the lower surface of the amorphous silicon film. In this method, after the base film is formed, nickel element is introduced, and first, the nickel element (the metal element) is held in contact with the surface of the base film.

  In this example, an aqueous solution of nickel acetate was applied to the surface of the base film, and the other steps were performed in the same manner as in Example 58 to obtain the state shown in FIG. As a method for introducing the nickel element, a sputtering method, a CVD method, and an adsorption method can be used in addition to the method using the solution.

Example 65
In Example 65, the crystalline silicon obtained in the previous step is irradiated with laser light in the state shown in FIG. 51E, FIG. 52A, or FIG. 53A. This is an example in which the crystallinity of an island-like pattern made of a film is further improved. When laser light is irradiated in the states of FIGS. 51E, 52A, and 53A, a predetermined annealing effect can be obtained with a relatively low irradiation energy density. This is presumably because the energy efficiency used for annealing is increased because the laser energy is irradiated to a small area.

Example 66
Example 66 relates to an example of manufacturing a bottom gate thin film transistor. FIG. 55 shows a manufacturing process of the thin film transistor of this example. First, a silicon oxide film 517 was formed as a base film over the glass substrate 516.

  Next, a gate electrode 518 is formed using an appropriate metal material or metal silicide material, and aluminum is used here. After forming the gate electrode 518, a silicon oxide film 519 functioning as a gate insulating film was formed. Further, an amorphous silicon film 520 was formed by plasma CVD. Next, as shown in FIG. 55B, a nickel acetate aqueous solution is applied, and the nickel element is in contact with the surface of the amorphous silicon film 520 as indicated by reference numeral 521 as a liquid film of the nickel acetate aqueous solution. Held in a state.

Next, heat treatment was performed at a temperature of 650 ° C. in a nitrogen atmosphere containing 3% by volume of hydrogen, and the amorphous silicon film 520 was crystallized. Thus, a crystalline silicon film 522 was obtained. This crystalline silicon film was subjected to heat treatment at a temperature of 650 ° C. in an oxygen atmosphere containing 5% by volume of HCl and 100 ppm (volume) of NF ₃ . A thermal oxide film 523 is formed by this heat treatment to obtain the state shown in FIG. 55C, and then the thermal oxide film 523 is removed.

  Next, the crystalline silicon film 522 and the silicon oxide film 519 were patterned to form the gate insulating film 525 and the active layer 526 of the thin film transistor. Further, as shown in FIG. 55D, a resist mask 524 is provided. In the state of FIG. 55D, impurity ions were implanted to form the source and drain regions. Here, P (phosphorus) ions were implanted in order to fabricate an N-channel thin film transistor. In this step, a source region 527 and a drain region 528 are formed.

  Thereafter, isotropic ashing was performed, and the resist mask 524 was entirely retracted. That is, as shown by reference numeral 529 in FIG. 55E, the resist mask 524 is made small as a whole. Thus, a resist mask 529 that was retracted was obtained. Next, in the state of FIG. 55E, another P ion implantation was performed.

  This step was performed with a dose smaller than the dose of P ions in the step shown in FIG. Thus, low concentration impurity regions indicated by reference numerals 530 and 531 were formed. Next, metal electrodes 532 and 533 were formed. Here, the electrode 532 serves as a source electrode, and the electrode 533 serves as a drain electrode. Thus, a bottom gate type thin film transistor was completed.

<< Aspects Assumptions of Example 67 >>
56 to 57 are explanatory diagrams of a manufacturing process of a thin film transistor (TFT), and are also explanatory diagrams of a TFT manufacturing process in Example 67 which will be described later. Therefore, based on FIGS. 56 to 57, a specific example of the invention that is a premise of the embodiment 67 will be described first.

  In FIG. 56A, a base film 535 and an amorphous silicon film 536 are sequentially stacked over a glass substrate 534, and a nickel (Ni) layer 537 is formed on the surface of the amorphous silicon film 536. Yes. By performing heat treatment in this state, the amorphous silicon film 536 is crystallized as shown in FIG. 56B, so that a crystalline silicon film 538 is formed. In this embodiment, the step of forming the nickel layer 537 is not an essential step, but since nickel functions as a catalyst for reducing the thermal energy necessary for crystallization, the heating temperature of the crystallization treatment is lowered and the treatment time is shortened. It becomes possible.

  As such a catalyst element, in addition to nickel (Ni), at least one element selected from Fe, Co, Ru, Rh, Pd, Os, Ir, Pt, Cu, and Au can be used. Nickel is most prominent in its catalytic effect. Note that a crystalline silicon film can be formed using a known technique or the like without using nickel element. Further, as the crystallization step, laser light may be irradiated instead of heat treatment. Further, after the crystalline silicon film is formed, light annealing by laser light, infrared light, or the like, or thermal annealing may be performed.

  FIG. 56C illustrates a thermal oxidation process. As the thermal oxide film 539 grows on the surface of the crystalline silicon film 538, that is, as Si—O bonds are formed, unbonded Si is generated. This excess Si diffuses into the crystalline silicon film 538 from the interface between the thermal oxide film 539 and the crystalline silicon film 538 and combines with the dangling bonds of Si existing at the crystal grain boundaries to form crystalline silicon. Defects at the grain boundaries of the film 538 are passivated. Thereby, the mobility of the TFT constituted by the crystalline silicon film 538 can be improved.

  Further, in a manufacturing process with subsequent heating, Si that has been passivated for defects does not easily separate from the crystalline silicon film 538 unlike H, so that hydrogen plasma treatment can be omitted. For example, for an N-channel TFT manufactured according to the method for manufacturing a semiconductor device according to the present invention, the mobility after hydrogen plasma treatment is increased by 10 to 20% compared to the mobility before hydrogen plasma treatment. This suggests that the defects of the crystalline silicon film 538 are sufficiently passivated in the thermal oxidation process, and also that the Si passivating the defects does not leave during the manufacturing process. .

  The purpose of the thermal oxidation process in the present invention is to supply Si for passivating defects at the grain boundaries of the crystalline silicon film, and considering that the crystalline silicon film 538 constitutes the active layer of the TFT, The thermal oxide film 539 may be grown to a film of about 200 to 500 angstroms without considering the film quality such as pressure resistance. Further, in the present invention, since the TFT is intended to be manufactured on a glass substrate or the like, the thermal oxidation process needs to be performed under a condition that allows distortion or deformation of the substrate caused by heating. For example, the upper limit of the heating temperature may be based on the strain point of the glass substrate.

In this embodiment, the thermal oxidation step is performed in an oxidizing atmosphere to which a fluorine compound is added. Specifically, thermal oxidation is performed in an atmosphere in which NF ₃ gas or the like is added to oxygen gas. By appropriately adjusting the concentration of NF ₃ gas, it is possible to grow a thermal oxide film to a film thickness of several hundred angstroms by heating for several hours to several tens of hours at a temperature below the strain point of the glass substrate. It is.

The growth of the thermal oxide film is promoted by adding a gas for supplying Cl radicals such as HCl to the oxidizing atmosphere in addition to a gas for supplying fluorine radicals such as NF ₃ gas. Since it takes time to form a thermal oxide film with a film thickness of several hundred angstroms by heating at a temperature below the strain point, for example, about 500 to 600 ° C., it is not appropriate. In an oxidizing atmosphere in which 450 ppm of NF ₃ gas is added to oxygen gas, a thermal oxide film of about 200 angstroms can be formed by heating at a temperature of 600 ° C. for 4 hours.

  Further, in the thermal oxidation step, fluorine radicals are concentrated and supplied to the convex portions on the surface of the crystalline silicon film 538, so that the thermal oxidation of the convex portions proceeds most and the thermal oxidation of the concave portions is suppressed. . Further, since the thermal oxide film 539 contains fluorine at a high concentration, the stress is relieved, so that the thermal oxide film 539 has a uniform thickness on the surface of the crystalline silicon film 538 in a state where the convex portions are rounded. Formed with.

  In the thermal oxidation process, it is necessary to determine the heating temperature and the heating time so that the distortion and deformation of the substrate are within an allowable range, so the concentration of the fluorine compound in the thermal oxidation atmosphere may increase. . As a result, there is a possibility that the thermal oxide film 538 contains a large amount of fluorine and an Si—F bond is formed. However, the thermal oxide film 539 is a film grown to supply Si for passivating the defects at the grain boundaries of the crystalline silicon film, and is formed as a film to be removed later. The gate insulating film is not required to have a high function and high reliability, and the instability such as Si—F bond existing in the thermal oxide film 539 and the pressure resistance are not questioned.

  FIG. 56D shows an active layer 540 and a gate insulating film 541 formed by patterning the crystalline silicon film 538 after removing the thermal oxide film 539. A thermal oxidation method can be employed to form the gate insulating film 541. However, a thermal oxide film obtained by thermal oxidation at a low temperature that allows deformation of the glass substrate has excellent film quality. Absent. For this reason, in this embodiment, in order to stably obtain a gate insulating film having predetermined characteristics, the gate insulating film is formed by a deposition method such as a plasma CVD method or a sputtering method.

  In this embodiment, since the surface of the active layer 540 (crystalline silicon film 538) is flattened through the thermal oxidation process, the gate insulating film can be formed even if it is formed by a deposition method. It can be formed with good. For this reason, the interface state between the gate insulating film and the active layer can be lowered.

  A crystalline silicon film obtained by irradiating a laser beam is excellent in crystallinity, but a ridge having a steep convex portion is formed on the surface thereof. For example, an amorphous film having a thickness of about 700 angstroms is formed. When laser annealing is performed after the silicon silicon film is heated and siliconized, a ridge having a height of about 100 to 300 angstroms is formed on the surface.

For example, by performing thermal oxidation for 12 hours in an atmosphere in which about 450 ppm of NF ₃ gas is added to oxygen gas, a thermal oxide film having a thickness of about 500 angstroms is formed. It is also possible to make it about angstrom. Therefore, the insulating film can be deposited with good coverage by the CVD method on the surface of the crystalline silicon film crystallized by the laser beam.

  FIG. 57A illustrates a process of doping impurity ions. The gate electrode 542 functions as a mask, and the source region 544, the drain region 545, and the channel region 546 are formed in a self-aligned manner. Further, as shown in FIG. 57B, an interlayer insulating film 547 and electrodes 548 and 549 are formed to complete the TFT.

Example 67
Example 67 is an example in which a TFT was manufactured using a silicon film crystallized by utilizing the catalytic action of a metal element that promotes crystallization of silicon. 56 and 57 are explanatory views of a manufacturing process of the TFT in this embodiment, and are cross-sectional views for each process. In this example, nickel was used as the metal element.

  As shown in FIG. 56A, a silicon oxide film is formed as a base film 535 to a thickness of 3000 angstrom on a glass substrate 534 (Corning 1737, strain point 667 ° C.) by a plasma CVD method or a low pressure thermal CVD method. To do. Next, a substantially intrinsic (I-type) amorphous silicon film 536 is formed to a thickness of 700 to 1000 angstroms by plasma CVD or low pressure thermal CVD. Here, the low-pressure thermal CVD method is used for both film formations, and the thickness of the amorphous silicon film 536 is set to 700 angstroms.

  In an oxidizing atmosphere, the surface of the amorphous silicon film 536 is irradiated with UV (ultraviolet light) to form an unillustrated oxide film having a thickness of several tens of angstroms on the surface, and then the surface of the oxide film is formed. A solution containing nickel element was applied. The oxide film is for improving the wettability of the surface of the amorphous silicon film 538 and preventing the solution from being repelled. In this example, a nickel acetate aqueous solution having a nickel content (weight) of 55 ppm was used as the solution containing nickel element.

  In this example, a nickel acetate solution was applied by a spinner and dried to form a nickel layer 537. Although the nickel layer 537 does not necessarily form a complete film, in this state, the nickel element is held in contact with the surface of the amorphous silicon film 536 through the oxide film (not shown). As the solution, a dilute solution of nickel salt is preferably used, but it can be preferably used as a solution having a nickel content of about 1 to 100 ppm.

Here, when the nickel concentration in the amorphous silicon film is 1 × 10 ¹⁶ atoms / cm ⁻³ or less, it is difficult to obtain an effect of promoting crystallization. On the other hand, when the nickel concentration is 5 × 10 ¹⁹ atoms / cm ³ or more, the characteristics of the obtained silicon film as a semiconductor are impaired, and the characteristics as a metal are exhibited. For this reason, the concentration of nickel in the nickel acetic acid solution, the number of times of application, the amount of application, etc. in advance so that the average nickel concentration in the finally obtained silicon film is 1 × 10 ^{16 to} 5 × 10 ¹⁹ atoms / cm ^3. Set the process conditions. Note that the nickel concentration may be measured by SIMS (secondary ion mass spectrometry).

  In the state where the nickel element is held on the surface of the amorphous silicon film 536 as shown in FIG. 56A, as shown in FIG. 536 was crystallized to form a crystalline silicon film 538. In order to crystallize silicon, it is necessary to heat at a temperature of 450 ° C. or higher, but at a temperature of about 450 ° C. to 500 ° C., it takes several tens of hours or more to crystallize the amorphous silicon film. It is desirable to heat at a temperature of ℃ or higher. Note that the heating temperature is not limited to the crystallization process illustrated in FIG. 56B, and the glass substrate needs to be in a range in which deformation or shrinkage of the glass substrate caused by the heating can be allowed.

  For example, the upper limit of the heating temperature may be the strain point of the substrate. In this example, since the glass substrate 534 having a strain point of 667 ° C. is used, the heating temperature is set to 620 ° C. and the heating is performed for 4 hours. With this heating, the crystal growth of silicon proceeds as nickel diffuses from the surface of the amorphous silicon film 536 toward the interface with the base film 535 in a direction substantially perpendicular to the surface of the glass substrate 534. Thus, a crystalline silicon film 538 is formed. This crystal growth proceeds in a direction perpendicular to the glass substrate 534. Such a crystal process is referred to as vertical growth.

  Note that, if necessary, crystallinity of the crystalline silicon film 538 may be further improved by performing light annealing or thermal annealing with laser light, infrared light, or ultraviolet light after the crystallization step. Further, light annealing and thermal annealing may be used in combination. However, in the case where laser annealing is performed, in order to effectively donate thermal energy to the crystalline silicon film 538 by laser light, the amorphous silicon film 536 that is a starting film of the crystalline silicon film 538 is used. The thickness is 1000 angstroms or less, preferably about 700 to 800 angstroms.

Next, a thermal oxide film 539 is formed to a thickness of 200 to 500 angstroms on the surface of the crystalline silicon film 538 by heating in an oxidizing atmosphere containing fluorine atoms. In this embodiment, the thermal oxide film 539 is formed to a thickness of about 200 Å by heating at 600 ° C. for 4 hours in an atmosphere in which 400 ppm (capacity) of NF ₃ is added to oxygen gas.

  As a result, the thickness of the crystalline silicon film 538 was about 700 angstroms, which was about 700 angstroms before the thermal oxide film 539 was formed. Since the crystalline silicon film 538 finally constitutes the active layer of the TFT, the thickness of the oxide film 539 is also taken into consideration so that an active layer having a required thickness can be obtained. It is necessary to determine the film thickness of the crystalline silicon film 536.

  As the thermal oxide film 539 is formed on the surface of the crystalline silicon film 538, unbonded Si is generated. This surplus Si diffuses into the crystalline silicon film 538 from the interface between the thermal oxide film 539 and the crystalline silicon film 538 and combines with the dangling bonds of Si existing at the crystal grain boundaries to form a crystalline property. The defect density of the crystal grain boundary of the silicon film 538 is reduced. Further, in the manufacturing process with subsequent heating, Si that has been passivating defects is not easily detached from the crystalline silicon film 538 unlike H. Therefore, the crystalline silicon film 538 is a semiconductor device such as a TFT. It is suitable for these materials.

Further, the surface of the crystalline silicon film 538 is rounded and flattened due to the difference in oxidation rate between the convex and concave portions. As described above, when the crystalline silicon film 538 is irradiated with laser light, since a ridge is formed on the surface thereof, thermal oxidation is performed so that the ridge can be flattened and removed as much as possible. In consideration of the thickness of the crystalline silicon film 538 after the process, thermal oxidation process conditions such as the thermal oxide film 539 thickness and NF ₃ gas concentration may be set.

  Next, as shown in FIG. 56D, the thermal oxide film 539 is removed by etching. In this etching, an etching solution or etching gas having a high etching rate between silicon oxide and silicon is used. As the etchant, buffer hydrofluoric acid or other hydrofluoric acid type etchant is preferably used. In this embodiment, the thermal oxide film 539 is removed by wet etching using buffer hydrofluoric acid.

  Next, the crystalline silicon film 538 is patterned into an island shape to form an active layer 540 of the TFT, and then a silicon oxide film is formed as a gate insulating film 541 to a thickness of 1000 angstrom by plasma CVD. Since the surface of the active layer 540 is planarized in the thermal oxidation process, the gate insulating film 541 can be deposited with good coverage. Thereafter, an aluminum film containing a small amount of scandium (not shown) is formed on the surface of the gate insulating film 541 to a thickness of 6000 angstrom by electron beam evaporation, and patterned to form a gate as shown in FIG. An electrode 542 was formed.

  Then, an oxide layer 543 was formed by performing anodic oxidation in the electrolytic solution using the gate electrode 542 as an anode. In this case, in an ethylene glycol solution containing 3% by weight of tartaric acid, a voltage is applied using the gate electrode 542 as an anode and platinum as a cathode, whereby an anodic oxide layer 543 having a dense structure is formed in 2000. An angstrom thickness was formed. Note that the film thickness of the anodic oxide 543 can be controlled by the voltage application time, and is also controlled in this embodiment.

Next, as shown in FIG. 57A, impurity ions imparting one conductivity type to the active layer 540 are formed by an ion implantation method or a plasma ion implantation method in order to form the source region 544 and the drain region 545. inject. In the case of forming an N-channel TFT, P (phosphorus) ions are implanted into the active layer 540 using phosphine diluted to 1 to 10% (capacity) with H ₂ gas. On the other hand, when manufacturing a P-channel TFT, B (boron) ions are implanted using diborane diluted to 1 to 10% (capacity). In this example, P ions and B ions were implanted by an ion implantation method, respectively, to fabricate N channel type and P channel type TFTs, respectively.

When impurity ions are implanted into the active layer 540, the gate electrode 542 and the surrounding anodic oxide 543 function as a mask, and regions into which the impurity ions are implanted are defined as a source region 544 and a drain region 545. A region where ions are not implanted is defined as channel 546. Note that doping conditions such as a dose and an acceleration voltage are controlled so that the concentration of impurity ions in the source region 544 and the drain 545 is 3 × 10 ¹⁹ to 1 × 10 ²¹ atoms / cm ³ . Further, after doping, laser light is irradiated to activate impurity ions implanted into the source region 544 and the drain region 545.

  Next, as shown as an interlayer insulating film 547 in FIG. 57B, a silicon oxide film was formed to a thickness of 7000 Å by plasma CVD. Next, contact holes were formed, and electrodes 548 and 549 connected to the source region 544 and the drain region 545 were formed using a material mainly containing aluminum.

  Finally, hydrogen plasma treatment was performed at a temperature of 300 ° C., whereby the thin film transistor shown in FIG. 57B was completed. The main purpose of this hydrogen plasma treatment is not to passivate defects in the active layer 540 but to passivate the interface between the active layer 540 and the electrodes 548 and 549 made of aluminum.

  The field-effect mobility of the P-channel TFT manufactured according to the manufacturing process of this example did not change significantly between before the hydrogen plasma treatment and after the hydrogen plasma treatment. This is because there is no passivation effect in the thermal oxidation step shown in FIG. 56C, and as described above, the field effect mobility of the P-channel TFT is not significantly improved by the passivation with only hydrogen plasma treatment. As expected, in P-channel TFTs, it is considered that passivation of crystal grain boundaries in the active layer 540 is not the best means for improving field effect mobility.

On the other hand, the N-channel TFT manufactured in accordance with the manufacturing process of this example had a field effect mobility of 200 cm ² · V ⁻¹ · s ⁻¹ before performing the hydrogen plasma treatment. After the treatment, the field effect mobility was only increased by about 10-20%. Conventionally, N-channel TFTs cannot be put to practical use unless hydrogen plasma treatment is performed. However, as in this embodiment, practical N-channel TFTs can be obtained only by adding NF ₃ and performing thermal oxidation treatment. This suggests that a type TFT can be manufactured.

  That is, in the hydrogen plasma treatment, there are not many crystal grain boundary defects in the active layer 540 passivated by hydrogen, and most of the crystal grain boundary defects are passivated in the thermal oxidation step shown in FIG. Is shown. Therefore, most of the defects that are passivated by the hydrogen plasma treatment of this embodiment are defects that occur after the thermal oxidation process, and are mainly defects that occur when the electrodes 548 and 549 are formed. In this embodiment, the defects in the crystal grain boundaries of the active layer 540 are passivated with Si. Since Si does not easily leave the active layer due to a thermal effect like H, a highly reliable TFT having excellent heat resistance can be formed according to the present invention.

Example 68
Example 68 is an example in which a TFT was manufactured using a silicon film crystallized by utilizing the catalytic action of a metal element that promotes crystallization of silicon. 58 and 59 are explanatory views of a manufacturing process of the TFT of this example, and are cross-sectional views for each process. In this example, nickel was used as the metal element.

  As shown in FIG. 58A, a silicon oxide film is formed as a base film 551 on a glass substrate 550 (Corning 1737, strain point 667 ° C.) to a thickness of 3000 angstrom by plasma CVD or low pressure thermal CVD. To do. Here, a plasma CVD method was used. Next, a substantially intrinsic amorphous silicon film 552 was formed to a thickness of 700 to 1000 angstroms by plasma CVD or low pressure thermal CVD. Here, the amorphous silicon film 552 is formed to a thickness of 1000 Å by plasma CVD.

  In an oxidizing atmosphere, UV (ultraviolet) light was irradiated on the surface of the amorphous silicon film 552, and an oxide film (not shown) was formed on the surface to a thickness of several tens of angstroms. This oxide film is for improving the wettability of the surface of the amorphous silicon film 552 and preventing the solution from being repelled. Next, a mask film 553 having an opening (opening) 554 made of a silicon oxide film having a thickness of 1500 angstroms was formed on the surface of the oxide film (not shown).

  The opening 554 has a slit-like shape in the longitudinal direction in a direction perpendicular to the paper surface (from the front to the depth). The width of the opening 554 is suitably 20 μm or more, and the dimension in the longitudinal direction is appropriately determined according to the substrate size and the like. Here, the width was 50 μm and the length in the longitudinal direction was 3 cm.

  Next, a nickel acetate solution containing 55 ppm (weight) of nickel element was applied by a spinner and dried to form a nickel layer 555. Although the nickel layer 555 does not necessarily form a complete film, in this state, the nickel element is formed of the amorphous silicon film 552 through the oxide film (not shown) in the opening 554 of the mask film 553. It is held in contact with the surface. As the solution, a dilute solution of nickel salt is preferably used, but it can be preferably used as a solution having a nickel content in the range of about 1 to 100 ppm (weight).

  Next, the amorphous silicon film 552 was crystallized by heating at a temperature of 620 ° C. for 4 hours, whereby a crystalline silicon film 556 was formed. By this heating, crystals grow vertically from the surface of the region 557 exposed in the opening 554 of the mask film 553 in the amorphous silicon film 552 toward the base film 551, so that the region 557 becomes a vertically grown region. .

  On the other hand, in the region 558, crystal growth proceeds in parallel with the surface of the substrate 550, as indicated by an arrow in FIG. 58B, starting from the vertical growth region 557. Such a crystallization process in which crystals grow in one direction is referred to as lateral growth. Accordingly, the region 558 in the crystalline silicon film 556 is a lateral growth region.

  Thereafter, the mask film 553 made of a silicon oxide film was removed. Next, as shown in FIG. 58C, a thermal oxide film 559 is formed to a thickness of 200 to 500 angstroms on the surface of the crystalline silicon film 556 by heating in an oxidizing atmosphere containing fluorine atoms. . Note that, if necessary, the crystallinity of the crystalline silicon film 556 may be further improved by performing light annealing with laser light or infrared light or thermal annealing before the thermal oxidation step. Further, light annealing and thermal annealing may be used in combination.

In the thermal oxidation process in this embodiment, the thermal oxide film 559 is heated to 600 ° C. for 12 hours in an atmosphere in which 450 ppm (capacity) of NF ₃ gas is added to an oxygen atmosphere, so that the thermal oxide film 559 has a thickness of about 500 Å. Formed. As a result, the thickness of the crystalline silicon film 556 was about 750 angstroms, which was about 1000 angstroms before the thermal oxidation process.

  As the thermal oxide film 559 is formed on the surface of the crystalline silicon film 556, unbonded Si is generated. The Si atoms are bonded to Si dangling bonds at the crystal grain boundaries of the crystalline silicon film 556, and the defects of the crystalline silicon film 556 are passivated. By forming the silicon oxide film 559 to about 500 angstroms with respect to the crystalline silicon film 556 having a thickness of 1000 angstroms, the defect density of the crystal grain boundaries of the crystalline silicon film 556 can be sufficiently reduced.

  Next, as shown in FIG. 58D, the thermal oxide film 559 was removed by etching. In this etching process, an etching solution or etching gas having a high etching rate between silicon oxide and silicon is used. In this embodiment, the thermal oxide film 559 is removed by wet etching using buffered hydrofluoric acid.

  Next, as shown in FIG. 58E, the crystalline silicon film 556 was etched into an island shape to form a TFT active layer 560. In this case, the active layer 560 is preferably composed of only the lateral growth region 558. Next, a silicon oxide film 561 constituting a gate insulating film is formed on the surface of the active layer 560 by a plasma CVD method or a low pressure CVD method. Here, a low pressure CVD method is used.

  Further, an aluminum film constituting the gate electrode 562 was deposited on the surface of the silicon oxide film 561 to a thickness of 5000 angstrom by sputtering. When aluminum contains a small amount of scandium in advance, generation of hillocks and whiskers can be suppressed in a subsequent heating step or the like, but here, 0.2% by weight of scandium was contained.

  Next, the surface of the aluminum film was anodized to form a very thin anodic oxide (not shown), and then a resist mask 563 was formed on the surface of the aluminum film. In this case, since the dense anodic oxide (not shown) is formed on the surface of the aluminum film, the mask 563 can be formed in close contact. Next, the aluminum film was etched using the resist mask 563 to form a gate electrode 562 as shown in FIG.

  Further, as shown in FIG. 59A, the gate electrode 562 was anodized with the resist mask 563 remaining, and a porous anodic oxide 564 was formed to a thickness of 4000 angstroms. In this case, since the resist mask 563 is in close contact with the surface of the gate electrode 562, the porous anodic oxide 564 is formed only on the side surface of the gate electrode 562.

  Next, as shown in FIG. 59B, after the resist mask 563 is removed, the gate electrode 562 is anodized again in an electrolytic solution to form a dense anodic oxide 565 having a thickness of 1000 angstroms. did. To make the anodic oxides 564 and 565, the electrolytic solution to be used may be changed. Among these, when forming the porous anodic oxide 564, for example, an acidic solution containing about 3 to 20% by weight of citric acid, oxalic acid, chromic acid or sulfuric acid may be used. Here, oxalic acid 5 A weight percent acidic aqueous solution was used.

  On the other hand, when the dense anodic oxide 565 is formed, for example, an electrolytic solution in which an ethylene glycol solution containing about 3 to 10% by weight of tartaric acid, boric acid or nitric acid is adjusted to a pH of about 7 may be used. Here, an ethylene glycol solution of 5% by weight of tartaric acid was used after adjusting to PH = 7.

  Next, as shown in FIG. 59C, the silicon oxide film 561 is etched using the gate electrode 562 and the porous anodic oxide 564 and dense anodic oxide 565 around the gate electrode 562 as a mask, thereby providing gate insulation. A film 566 was formed. Next, as shown in FIG. 59 (D), after removing the porous anodic oxide 564, the gate electrode 562, the dense anodic oxide 565, and the gate insulating film 566 are masked by an ion doping method. An impurity imparting conductivity is implanted into the layer 560.

  In this example, P (phosphorus) ions were doped using phosphine as a doping gas in order to form an N-channel TFT. During doping, conditions such as a dose amount and an acceleration voltage are controlled so that the gate insulating film 564 functions as a semi-transmissive mask. As a result of the doping, a region not covered with the gate insulating film 564 was implanted with phosphorus (P) ions at a high concentration to form a source region 567 and a drain region 568.

  On the other hand, in the region covered only by the gate insulating film 566, P ions are implanted at a low concentration, and low concentration impurity regions 569 and 570 are formed. Further, since the impurity is not implanted into the region immediately below the gate electrode 562, a channel region 571 is formed. After the doping process, thermal annealing, laser annealing, or the like is performed to activate the doped P ions. Here, thermal annealing was applied.

  Since the low-concentration impurity regions 569 and 570 function as high-resistance regions, they contribute to reduction of off-state current. In particular, the low concentration impurity region 570 on the drain 568 side is called LDD. In addition, when the dense anodic oxide 564 is sufficiently thick, an offset structure in which the impurity region is shifted from the end face of the gate electrode 562 can be obtained, so that off-state current can be further reduced.

  Next, as shown in FIG. 59E, a silicon oxide film having a thickness of 5000 angstroms was formed as an interlayer insulator 572 by a plasma CVD method. Note that as the interlayer insulator 572, a single layer film of a silicon nitride film or a stacked film of a silicon oxide film and a silicon nitride film may be formed instead of the single layer film of a silicon oxide film.

  Next, the interlayer insulator 572 made of a silicon oxide film is etched by etching to form contact holes in the source region 567 and the drain region 568, and then an aluminum film is formed to a thickness of 4000 angstroms by sputtering. Filmed. This was patterned to form electrodes 573 and 574 in the contact holes of the source region 567 and the drain region 568.

  Finally, heat treatment was performed at a temperature of 300 ° C. in a hydrogen atmosphere. The hydrogen plasma treatment is not intended to passivate defects in the active layer 560, but mainly to passivate the interface between the active layer 560 and the electrodes 573 and 574 made of aluminum. Through the above steps, a TFT having a world LDD structure was manufactured as shown in FIG.

In the N-channel TFT manufactured according to the manufacturing process of this example, the field effect mobility after the hydrogen plasma treatment was only increased by about 10 to 20% before the hydrogen plasma treatment was performed. . Conventionally, an N-channel TFT cannot be put into practical use without a hydrogen plasma treatment, but the crystal grains of the active layer 560 can be obtained only by a thermal oxidation treatment to which NF ₃ is added as in the step of FIG. 58 (C). This suggests that the defects in the field are effectively passivated.

Example 69
Example 69 is an example in which a CMOS type TFT in which an N channel type TFT and a P channel type TFT are complementarily combined is manufactured. 60 to 61 are explanatory views of a manufacturing process of the TFT of this example.

  First, as shown in FIG. 60A, a base film 576 made of a silicon oxide film having a thickness of 2000 angstroms was formed on a glass substrate (Corning 1737) 575. Next, an intrinsic (I type) amorphous silicon film was formed to a thickness of 700 angstroms by plasma CVD or low pressure thermal CVD. Then, a crystalline silicon film 577 was formed by the method shown in Example 67. Note that the amorphous silicon film may be crystallized by the method of Example 68, or by an appropriate crystallization method such as heat treatment or laser irradiation. In these cases, the following steps are the same.

As shown in FIG. 60B, thermal oxidation is performed for 2 hours at a temperature of 600 ° C. in an oxygen atmosphere having an NF ₃ concentration of 400 ppm to form a thermal oxide film 578 having a thickness of 200 angstroms. The defects in the grain boundaries of the conductive silicon film 577 were passivated with Si. As a result, the crystalline silicon film 577 is suitable as a semiconductor material such as a TFT.

  Next, after removing the thermal oxide film 578 using an etchant made of buffer hydrofluoric acid, the crystalline silicon film 577 was patterned into an island shape to form an active layer 579 and an active layer 580, respectively. Further, a silicon oxide film 581 constituting a gate insulating film was deposited to a thickness of 1500 angstrom by plasma CVD. Note that the active layer 579 constitutes an N-channel TFT, and the active layer 580 constitutes a P-channel TFT.

  Next, an aluminum film constituting the gate electrodes 582 and 583 was deposited to a thickness of 4000 angstroms by sputtering. In the aluminum film, 0.2% by weight of scandium was previously contained to suppress generation of hillocks and whiskers. Next, the aluminum film was anodized in an electrolytic solution to form a dense anodized film 584 of about 100 angstroms on the surface. Next, a photoresist mask 585 was formed on the surface of the anodic oxide film, and the aluminum film was patterned to form gate electrodes 582 and 583, respectively.

  Further, the gate electrodes 582 and 583 were anodized again while wearing the photoresist mask 585 to form anodic oxides 586 and 587. For example, an acidic solution containing 3 to 20% by weight of citric acid, oxalic acid, chromic acid or sulfuric acid may be used as the electrolytic solution. In this example, a 4% by weight oxalic acid aqueous solution was used.

  Porous anodic oxides 586 and 587 are formed only on the side surfaces of the gate electrodes 582 and 583 when the photoresist mask 585 and the anodic oxide film 584 are present on the surfaces of the gate electrodes 582 and 583. The growth distance of the porous anodic oxides 586 and 587 can be controlled by the processing time of the anodic oxidation, and this growth distance determines the length of the low concentration impurity region (LDD region). In this example, porous anodic oxides 586 and 587 were grown to a length of 7000 angstroms.

  Next, after removing the photoresist mask 585, the gate electrodes 582 and 583 were anodized again to form dense and strong anodic oxide films 588 and 589 as shown in FIG. In this example, an ethylene glycol solution of 3% by weight tartaric acid was used as the electrolytic solution after neutralizing to pH 6.9 with aqueous ammonia.

Next, P (phosphorus) ions were implanted into the island-like active layers 579 and 580 by ion doping using the gate electrodes 582 and 583 and the porous anodic oxides 586 and 587 as a mask. As a doping gas, phosphine diluted with hydrogen to 1 to 10% by volume was used. In the doping, the acceleration voltage is set to 60 to 90 kV and the dose amount is set to 1 × 10 ¹⁴ to 8 × 10 ¹⁵ atoms / cm ^{2. In} this embodiment, the acceleration voltage is set to 80 kV and the dose amount is set to 1 × 10 ^15. Atom / cm ² .

  At this time, phosphorus (P) ions do not pass through the gate electrodes 582 and 583 and the porous anodic oxides 586 and 587 but pass through the gate insulating film 581 and are injected into the island-like silicon 589 and 580. . As a result, N-type impurity regions 590 to 593 are formed as shown in FIG.

  Next, as shown in FIGS. 61E to 61F, after the dense anodic oxide film 584 is removed with buffer hydrofluoric acid, a porous anodic oxide 586 is mixed with a mixed acid obtained by mixing phosphoric acid, acetic acid and nitric acid. 587 was removed. Since the porous anodic oxides 586 and 587 can be easily removed, the dense and strong anodic oxides 588 and 589 are not etched.

Next, phosphorus ions were doped again. The acceleration voltage is 60 to 90 kV and the dose is 1 × 10 ¹² to 1 × 10 ¹⁴ atoms / cm ^{2. In} this embodiment, the acceleration voltage is 80 kV and the dose is 1 × 10 ¹⁴ atoms / cm ² . did. In this case, phosphorus ions do not pass through the gate electrodes 582 and 583 but pass through the gate insulating film 581 and are implanted into the active layers 579 and 580. Therefore, the region into which phosphorus ions are implanted twice becomes N-type high-concentration impurity regions 594 to 597, and the region into which phosphorus ions are implanted once becomes N-type low-concentration impurity regions 598 to 601.

As shown in FIG. 61G, a region to be an N-channel TFT is covered with polyimide or a heat resistant resist 602. Here, polyimide is used. Thereafter, boron ions were ion-doped in order to invert the conductivity type of the active layer 580 from N-type to P-type. Diborane diluted to about 1 to 10% by volume with hydrogen was used as the doping gas, the acceleration voltage was 80 kV, and the boron dose was 2 × 10 ¹⁵ atoms / cm ² .

  The region covered with polyimide 602 remains N-type because boron is not implanted. Accordingly, in the active layer 579, the high-concentration impurity regions 594 and 595 correspond to the source region and drain region of the N-channel TFT, respectively, and the region 603 directly below the gate electrode 582 is not implanted with phosphorus ions and boron ions. It remains true and corresponds to the TFT channel.

  In boron ion doping, since the amount of boron implanted is large, a low concentration impurity region (LDD region) is not formed, and only P-type high concentration impurity regions 604 and 605 are formed. The high concentration impurity regions 604 and 605 correspond to the source region and drain region of the P-channel TFT, respectively. Further, the region 606 directly below the gate electrode 583 remains intrinsic because phosphorus ions and boron ions are not implanted, and becomes a TFT channel.

  Subsequently, the resist 602 was removed, and as shown in FIG. 61H, a silicon oxide film having a thickness of 1 μm was formed as an interlayer insulating film 607 by a plasma CVD method, and a contact hole was formed therein. Source and drain region electrodes and wirings 608 to 610 were formed in this contact hole by a multilayer film of titanium and aluminum. Finally, heat treatment was performed for 2 hours in a hydrogen atmosphere at a temperature of 350 ° C. The CMOS thin film transistor was completed through the above steps.

  In this embodiment, since a CMOS structure in which an N-type TFT and a P-type transistor are complementarily combined is formed, power can be reduced when driving the TFT. In addition, since the low-concentration impurity region 599 is disposed between the channel 603 and the drain region 595 of the N-channel TFT, generation of a high electric field between the channel 603 and the drain 595 can be prevented.

The conditions for the thermal oxidation process with the addition of NF ₃ are not limited to those described in Examples 67 to 69, and the distortion or deformation of the substrate on which the TFT formed in the thermal oxidation process is formed is within an allowable range. Therefore, the concentration of NF _{3 in} the oxygen atmosphere should be determined so that the thermal oxide film grows to a thickness of several hundred angstroms by heating for several hours at a temperature below the strain point of the glass substrate. That's fine. In addition, when a highly heat-resistant substrate such as a quartz substrate is used, it is also performed under a higher temperature condition.

  Moreover, since the Corning 1737 glass whose distortion point is 667 degreeC was used for the glass substrate in Examples 67-69, although the heating temperature in a thermal oxidation process was 600 degreeC, the distortion point is 593 degreeC, for example. When glass is used, the heating temperature in the thermal oxidation step is preferably about 500 to 550 ° C.

《Application example》
The semiconductor device of the present invention is applied to display devices for various electric appliances, various integrated circuits, or circuits for replacing conventional IC circuits. 62 to 63 illustrate some of them. FIG. 62A shows a portable information terminal, and FIG. 62B shows an HMD (head mounted display) used for viewing images from an endoscope, car training, crane training, and the like. FIG. 62C shows a car navigation system. FIG. 61D shows a mobile phone, FIG. 63E shows a video camera, and FIG. 61F shows a projection. The semiconductor device of the present invention is not limited to these, and is used for display devices of various electric devices, circuits in place of conventional IC circuits, various integrated circuits, and the like.

The figure which shows the fine structure of the crystalline silicon film obtained by this invention (an optical microscope photograph: 450 times). The figure which shows the fine structure of the crystalline silicon film obtained by this invention (an optical microscope photograph: 450 times). The figure which shows the fine structure of the crystalline silicon film obtained by this invention (TEM: 50000 times). The figure which shows the fine structure of the crystalline silicon film obtained by this invention (TEM: 250,000 times). The figure which shows an example in the typical aspect of the manufacturing process of the crystalline silicon film which concerns on this invention. The figure which shows an example in the typical aspect of the manufacturing process of the semiconductor device using the crystalline silicon film which concerns on this invention. The figure which showed typically the form of the crystal growth assumed based on the result observed from many micrographs about the crystalline silicon film concerning this invention. FIG. 6 is a schematic diagram for explaining subthreshold characteristics (S value) and the like of a semiconductor device. FIG. 6 is a graph showing various characteristics such as a subthreshold characteristic (S value) of a semiconductor device using a crystalline silicon film according to the present invention. FIG. 6 is a graph showing various characteristics such as a subthreshold characteristic (S value) of a semiconductor device using a crystalline silicon film according to the present invention. FIG. 6 is a graph showing various characteristics such as a subthreshold characteristic (S value) of a semiconductor device using a crystalline silicon film according to the present invention. The schematic diagram for demonstrating the characteristic of the ring oscillator which combined the circuit which combined N channel type TFT and P channel type TFT. The figure which shows the oscilloscope (oscillation waveform) by the ring oscillator which combined the circuit which combined N channel type TFT and P channel type TFT using the crystalline silicon film which concerns on this invention. FIG. 6 is a diagram showing a measured value of a gate current value of a planar thin film transistor using a crystalline silicon film according to the present invention. FIG. 6 is a diagram showing a measured value of a gate current value of a planar thin film transistor using a crystalline silicon film according to the present invention. The figure which shows the result of having measured the density | concentration distribution of Ni element in the film cross-section direction at the time of forming a thermal oxide film after crystallizing an amorphous silicon film using Ni. The figure which shows the result of having measured the density | concentration distribution of Ni element in the film cross-section direction at the time of forming a thermal oxide film after crystallizing an amorphous silicon film using Ni. The figure which shows the result of having measured the density | concentration distribution of Cl in the film cross-sectional direction at the time of forming a thermal oxide film after crystallizing an amorphous silicon film using Ni. The figure which shows the result of having measured the density | concentration distribution of Ni element in the film cross-section direction at the time of forming a thermal oxide film after crystallizing an amorphous silicon film using Ni. The figure which shows the result of having measured the density | concentration distribution of Ni element in the film cross-section direction at the time of forming a thermal oxide film after crystallizing an amorphous silicon film using Ni. The figure which shows the result of having measured the density | concentration distribution of Cl in the film cross-sectional direction at the time of forming a thermal oxide film after crystallizing an amorphous silicon film using Ni. FIG. 6 shows a manufacturing process in Example 4; FIG. 9 shows a manufacturing process in Example 9. FIG. 10 shows a manufacturing process in Example 10. FIG. 16 shows a manufacturing process in Example 12. FIG. 16 shows a manufacturing process in Example 13. FIG. 16 shows a manufacturing process in Example 16; FIG. 18 shows a manufacturing process in Example 21. FIG. 22 shows a manufacturing process in Example 22. FIG. 24 shows a manufacturing step in Example 24. FIG. 25 shows a manufacturing step in Example 25. FIG. 25 shows a manufacturing step in Example 28. FIG. 16 shows a manufacturing process in Example 30. FIG. 16 shows a manufacturing process in Example 31. FIG. 25 shows a manufacturing step in Example 33. FIG. 16 shows a manufacturing process in Example 34; FIG. 18 shows a manufacturing process in Example 37. The schematic diagram explaining the phenomenon at the time of the laser beam irradiation to the crystalline silicon film surface. FIG. 25 shows a manufacturing step in Example 39. FIG. 16 shows a manufacturing process in Example 41. FIG. 16 shows a manufacturing process in Example 42. FIG. 24 shows a manufacturing step in Example 44. FIG. 25 shows a manufacturing step in Example 45. FIG. 46 shows a manufacturing process in Example 48. FIG. 18 shows a manufacturing process in Example 50. FIG. 25 shows a manufacturing step in Example 52. FIG. 18 shows a manufacturing process in Example 53. FIG. 25 shows a manufacturing step in Example 54. FIG. 46 shows a manufacturing process in Example 55. FIG. 46 shows a manufacturing process in Example 58; FIG. 16 shows a manufacturing process in Example 60. FIG. 46 shows a manufacturing process in Example 61. FIG. 18 shows a manufacturing process in Example 62. FIG. 18 shows a manufacturing step in Example 63. FIG. 46 shows a manufacturing step in Example 66. FIG. 18 shows a manufacturing process in Example 67. FIG. 18 shows a manufacturing process in Example 67. FIG. 46 shows a manufacturing process in Example 68. FIG. 46 shows a manufacturing process in Example 68. FIG. 46 shows a manufacturing step in Example 69. FIG. 46 shows a manufacturing step in Example 69. 4A and 4B are diagrams showing some examples of various application examples of the semiconductor device of the present invention. 4A and 4B are diagrams showing some examples of various application examples of the semiconductor device of the present invention.

Explanation of symbols

1, 8, 20, 39, 57... Glass substrate, quartz substrate, etc. 2, 9, 21, 40, 58... Base film (silicon oxide film, silicon oxynitride film, etc.)
3, 10, 86, 93, 104... Amorphous silicon film 4, 13, 87, 96, 170... Water film of solution containing nickel salt 5, 15, 88, 98, 171.・ Crystalline silicon film 6, 16, 89, 99, 172... Thermal oxide film (metal element contained in high concentration in the film)
7, 15, 90, 98, 173... Crystalline silicon film with reduced or removed metal element concentration 17, 22, 41, 59, 60... Reduced or removed metal element concentration and patterned. Crystal silicon film 11, 94, 177, 271 ... Mask 12, 95, 178, 272 ... Opening 17, 26 ... Pattern 27 Anodized film 29 Silicon oxide film 28 Anodized film 30 Source region 31 Channel formation region 32 Channel region 33 LDD region 34 Drain region 35, 201 Interlayer insulating film 36 Source electrode 37 Drain electrode

Claims (12)

An amorphous silicon film is formed on a base insulating film containing a halogen element formed on a substrate ,
A metal element that promotes crystallization of silicon is intentionally introduced into the amorphous silicon film,
Forming a crystalline silicon film by crystallizing the amorphous silicon film by a first heat treatment;
Patterning the crystalline silicon film to form an active layer of a semiconductor device;
Irradiating the active layer with laser light or strong light,
A second thermal treatment is performed in an oxidizing atmosphere containing a halogen element to form a first thermal oxide film on the surface of the crystalline silicon film, and the metal element present in the active layer is removed or reduced. ,
Removing the first thermal oxide film;
A second thermal oxide film is formed on the surface of the active layer by performing another thermal oxidation in an atmosphere containing a halogen element ;
A method for manufacturing a semiconductor device, wherein an insulating film containing a halogen element is formed over the second thermal oxide film. In the manufacturing method of the semiconductor device according to claim 1,
The method for manufacturing a semiconductor device, wherein the active layer has an inclined shape whose side surface forms an angle of 20 ° to 50 ° with the insulating surface. In the manufacturing method of the semiconductor device according to claim 1 or 2 ,
The first heat treatment is performed at a temperature of 750 ° C. to 1100 ° C.,
The method for manufacturing a semiconductor device is characterized in that the temperature of the second heat treatment is higher than the temperature of the first heat treatment. In the method for manufacturing a semiconductor device according to any one of claims 1 to 3,
A method for manufacturing a semiconductor device, wherein the second heat treatment is performed to getter the metal element present in the active layer into the first thermal oxide film. In the manufacturing method of the semiconductor device in any one of Claims 1 thru | or 4 ,
A method for manufacturing a semiconductor device, wherein a crystal in a crystalline silicon film obtained by crystallizing the amorphous silicon film is a crystal in which crystal lattices are continuously connected. In the manufacturing method of the semiconductor device in any one of Claims 1 thru | or 4 ,
A method for manufacturing a semiconductor device, wherein a crystal in a crystalline silicon film obtained by crystallizing the amorphous silicon film is a thin rod-shaped crystal or a thin flat rod-shaped crystal. In the manufacturing method of the semiconductor device in any one of Claims 1 thru | or 4 ,
The crystal in the crystalline silicon film obtained by crystallizing the amorphous silicon film is a plurality of thin rod-like crystals or thin flat rod-like crystals, which are grown in parallel or almost in parallel at intervals. A method for manufacturing a semiconductor device. In the manufacturing method of the semiconductor device in any one of Claims 1 thru | or 7 ,
A method for manufacturing a semiconductor device, wherein a quartz substrate is used as a substrate on which the amorphous silicon film is formed. In the method for manufacturing a semiconductor device according to any one of claims 1 to 8,
The metal element that promotes the crystallization of silicon is one or more elements selected from Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, and Au. A method for manufacturing a semiconductor device. In the method for manufacturing a semiconductor device according to any one of claims 1 to 9,
A method for manufacturing a semiconductor device, comprising: performing annealing in a plasma atmosphere containing oxygen and hydrogen after removing the first thermal oxide film. In the method for manufacturing a semiconductor device according to any one of claims 1 to 10,
A method for manufacturing a semiconductor device, wherein the concentration of oxygen contained in the amorphous silicon film is 5 × 10 ¹⁷ cm ⁻³ to 2 × 10 ¹⁹ cm ⁻³ . In the method for manufacturing a semiconductor device according to any one of claims 1 to 11,
The method for manufacturing a semiconductor device, wherein the insulating film containing a halogen element is a silicon oxide film containing a halogen element or a silicon oxynitride film containing a halogen element.