JP3612017B2 - Active matrix display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for efficiently performing doping and other chemical and physical treatments in a low-temperature process. The present invention also relates to a connection structure between a thin film transistor and a pixel electrode provided in a pixel of an active matrix display device.
[0002]
[Prior art]
Conventionally, a thermal diffusion method or an ion implantation method is known as a doping technique. The thermal diffusion method is a method in which impurities are diffused into a semiconductor in a high temperature atmosphere of 1000 to 1200 degrees, and the ion implantation method is a method in which ionized impurities are accelerated by an electric field and implanted into a predetermined place.
[0003]
However, the diffusion coefficient D of impurities is D = D₀exp [-E_a/ KT] is exponentially dependent on the absolute temperature T as shown by: Where D₀Is the diffusion coefficient at T = ∞ and E_aIs the active energy and k is the Boltzmann coefficient. Therefore, in order to diffuse impurities into the semiconductor efficiently, it is desirable to carry out at a high temperature as much as possible. In the thermal diffusion method, it is generally carried out at a high temperature process of 1000 ° C. or more. Further, the ion implantation method requires a post heat treatment step at a temperature of 600 ° C. to 950 ° C. in order to activate impurities and recover defects.
[0004]
In recent years, some active matrix type liquid crystal display devices using TFTs (thin film transistors) provided on a glass substrate as pixel switching elements have been put into practical use. Generally, it is made of conductive amorphous silicon. Also, the structure of the TFT is an inverted stagger type, and parasitic capacitance is likely to occur due to structural problems. Therefore, it has been studied to use a TFT in which the source and drain regions are formed in a self-aligned manner (self-alignment). In order to form the source and drain regions in a self-aligned manner, an ion implantation method or an ion shower method is used. Had to be used. However, these methods require a post-heat treatment step at a temperature of 600 ° C. to 950 ° C. for activation of impurities and recovery of defects as described above, and the heat resistance temperature of a general inexpensive glass substrate is 600 ° C. Considering that it is -700 degree | times, it was difficult to use industrially.
[0005]
As a method for solving such a problem of thermal damage given to a glass substrate, a doping technique by laser light irradiation is known. As one of the methods, there is a method in which a thin film of an impurity is formed on a semiconductor surface to be doped, the thin film of the impurity and the semiconductor surface are melted by laser light irradiation, and the impurity is dissolved.
[0006]
The above-described method of doping by irradiation with excimer laser light does not cause thermal damage to the glass substrate, and thus has the advantage that generation of defects due to thermal damage can be suppressed, but undergoes a step of forming an impurity film. There was a need. Conventionally, a coating method such as a spin coat method has been used for the formation of the film. However, in this process, if the film thickness is not uniform, the doping concentration of impurities is different, which is not an ideal method. Further, this film is usually formed using an organic solvent as a solvent. In that case, undesirable elements such as carbon, oxygen, and nitrogen may enter the semiconductor and deteriorate the characteristics.
[0007]
[Problems to be solved by the invention]
The present invention has been made in view of the problems of complicated processes and intrusion of foreign elements, which are problems in the doping technique using the above laser light, particularly excimer laser light. Accordingly, the present invention intends to perform doping using a high-purity doping gas without using a liquid-phase or solid-phase doping material, thus simplifying the process and invading foreign elements. The purpose is to prevent this. Further, it is an object of the invention to increase the doping efficiency.
Furthermore, the present invention has an object of performing doping on a wide variety of materials (insulators, conductors) and their surfaces in addition to doping on semiconductor materials, and improving the materials accompanying the materials and their surfaces. For example, doping of phosphorus into the silicon oxide film.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the present invention is directed to irradiating a sample semiconductor surface with laser light in a high purity reactive gas atmosphere containing an impurity imparting one conductivity type, thereby providing the one conductivity type. In this method, the sample semiconductor is doped with an impurity that imparts. However, according to the knowledge of the present inventor, if the sample semiconductor is at a low temperature such as room temperature, the diffusion of elements is not sufficient.
[0009]
Accordingly, one of the present invention is to promote the diffusion of impurity elements by heating the sample at the time of laser irradiation and maintaining the temperature at least 200 ° C. or more, and try to dope a high concentration of impurities. Is. Although the heating temperature of the substrate varies depending on the type of semiconductor, in the case of polysilicon (polycrystalline silicon) and semi-amorphous silicon, 250 to 500 ° C., preferably 300 to 400 ° C. is suitable.
[0010]
When the sample is heated and irradiated with the laser in this way, not only the impurities are easily diffused, but also the semiconductor whose crystallinity has been temporarily lowered by the laser irradiation can be given a sufficient thermal relaxation time. Easy to recover crystallinity. Laser irradiation, particularly pulse laser irradiation, is typical rapid heating and rapid cooling when the sample is not heated to an appropriate temperature, so that the semiconductor tends to exhibit an amorphous state. That is, it is instantaneously heated to 1000 ° C. or higher, but after several hundred nsec, it is lowered to room temperature. If the sample is heated as silicon within the above range, the time required for the temperature to drop to around 500 ° C., which is the lower limit of the crystallization temperature of silicon, is 10 times or more that at room temperature. Calculated. At this stage, when the laser irradiation time continues for a certain time or more, the silicon melts, and the impurities penetrate into the interior by the convection of the melt. In addition, when the pulse does not continue for a certain time or more, silicon crystallizes in a solid phase and becomes a so-called semi-amorphous. At that time, impurities diffuse in the solid phase inside.
[0011]
It is undesirable for the temperature to be too high. This is because at a high temperature, the reactive gas itself decomposes and adheres not only to the sample but also to its holder and the like, thereby reducing the efficiency of gas utilization.
[0012]
It is also undesirable to keep the temperature higher than the crystallization temperature of the semiconductor. This is particularly undesirable in semiconductors with many defects such as polycrystalline semiconductors, amorphous semiconductors, and semi-amorphous semiconductors. This is because if a crystalline semiconductor is doped while being heated at a temperature equal to or higher than the crystallization temperature, there arises a problem of difficulty in controlling valence electrons due to generation of levels. It is said that amorphous silicon is thermally changed to polysilicon at 500 to 550 ° C., and therefore, this temperature is preferably lower than this temperature, preferably 100 ° C. or lower (that is, 400 to 450 ° C. or lower). desired. In addition, in a TFT using amorphous silicon (referred to as a-Si: TFT), when the configuration of the present invention is used, the element is destroyed when the a-Si: TFT is heated to a temperature of 350 ° C. or more. In this case, it is appropriate to perform heating at a temperature of 350 ° C. or less. The same applies to other semiconductors.
[0013]
According to another aspect of the present invention, in the doping technique from the gas phase using the above laser light, particularly excimer laser light, when a plurality of dopings are performed using different doping gases, a single laser light is used. An object of the present invention is to solve the problem of reduction in doping efficiency due to the fact that the light absorption characteristics of the doping gas are different and the decomposition characteristics are different depending on the type of gas. Therefore, a configuration is adopted in which electromagnetic energy is applied to decompose the reactive gas in a reactive gas atmosphere containing an impurity imparting one conductivity type at the time of laser irradiation. At this time, when the laser beam is further irradiated, the doping efficiency can be further improved by heating the semiconductor to be doped, which is a sample, at an appropriate temperature as in the first invention.
[0014]
The impurity imparting one conductivity type in the present invention is a trivalent impurity, typically B (boron), if a silicon semiconductor (silicon) is used as a semiconductor and a p-type is imparted. If N-type is imparted, a pentavalent impurity, typically P (phosphorus), As (arsenic), or the like can be used. AsH is a reactive gas containing these impurities.₃, PH₃, BF₃, BCl₃, B (CH₃)₃Etc. can be used.
[0015]
As a semiconductor, if a TFT is manufactured, an amorphous silicon semiconductor thin film formed by vapor deposition or sputtering is generally used. The present invention can also be applied to a polycrystalline or single crystal silicon semiconductor manufactured by liquid phase growth. Furthermore, it is needless to say that the semiconductor is not limited to a silicon semiconductor and may be other semiconductors.
[0016]
As the laser light, it is useful to use a pulse oscillation type excimer laser device. This is because in a pulsed laser, the sample is heated instantaneously and is limited to the surface only, and does not affect the substrate. Since heating by a laser is local, in a continuous wave laser (such as an argon ion laser), the heated portion may be peeled off due to a significant difference in thermal expansion between the heated portion and the substrate. In this respect, in the pulse laser, the thermal relaxation time is overwhelmingly smaller than the reaction time of mechanical stress such as thermal expansion, and no mechanical damage is caused. Of course, the impurities on the substrate are hardly thermally diffused.
[0017]
In particular, excimer laser light is ultraviolet light that is efficiently absorbed by many semiconductors including silicon and has a short pulse duration of 10 nsec. In addition, the excimer laser has already been used in experiments in which an amorphous silicon thin film is crystallized by laser irradiation to obtain a highly crystalline polycrystalline silicon thin film. As a specific type of laser, it is appropriate to use an ArF excimer laser (wavelength 193 nm), a XeCl excimer laser (wavelength 308 nm), a XeF excimer laser (wavelength 351 nm), a KrF excimer laser (248 nm), or the like.
[0018]
In the configuration of the present invention, as a means for heating the substrate, a conductive type in which a nichrome wire, a Kanthal wire or other heating element is directly incorporated in the holder may be used, but an infrared lamp or other radiation type May be used. However, since the substrate temperature has a great influence on the impurity doping concentration and depth, it is desired to precisely control the substrate temperature. Therefore, a temperature sensor such as a thermocouple is indispensable for the sample.
[0019]
In the configuration of the present invention, high frequency energy of 13.56 MHz is generally used as electromagnetic energy applied to decompose a reactive gas for doping (referred to as doping gas). Due to the decomposition of the doping gas by this electromagnetic energy, doping can be performed efficiently even when laser light that cannot directly decompose the doping gas is used. The type of electromagnetic energy is not limited to a frequency of 13.56 MHz. For example, when a microwave of 2.45 GHz is used, a higher activation rate can be obtained. Furthermore, an ECR condition generated by the interaction between a 2.45 GHz microwave and an 875 Gauss magnetic field may be used. It is also effective to use light energy that can directly decompose the doping gas.
[0020]
In the above description, the doping technique in the semiconductor has been described. However, the present invention is not limited to this, and can be widely applied. For example, the present invention can also be used when a trace element that improves the surface material is added to a portion of a specific thickness on the surface of a metal by several percent. For example, the present invention may be carried out in ammonia on the iron surface, nitrogen may be doped, and the surface may have several to several hundred nm as iron nitride.
[0021]
Alternatively, the present invention can be carried out on oxides and the effect can be obtained. For example, it is possible to raise the superconducting critical temperature by carrying out the present invention in a lead chloride vapor in a bismuth-based oxide high-temperature superconductor thin film and incorporating lead. Conventionally, it is known that there are several kinds of bismuth-based oxide high-temperature superconductors, and the maximum critical temperature is about 110K. However, it has been difficult to obtain a phase having a critical temperature exceeding 100K. It has been known that when lead is added, a phase exceeding 100 K can be easily obtained. However, in the thin film manufacturing process, lead tends to evaporate to the outside due to the influence of substrate heating. However, since the present invention is a non-thermal equilibrium reaction, lead can be effectively incorporated into the thin film forming material. Similarly, in recent years, it has been attracting attention as a functional material for semiconductor integrated circuits, particularly semiconductor memories, and can be applied to PZT (lead zirconia titanium oxide) which is a ferroelectric containing lead.
[0022]
Also, an insulator such as silicon oxide can be used when adding a small amount of impurities. As already used in semiconductor processes, silicon oxide is often made into phosphorus glass by containing about several percent of phosphorus. Of course, it is also possible to include phosphorus in silicon oxide using the present invention. For example, 1 × 10²⁰~ 3x10²⁰cm^-3Phosphorus can be diffused at a concentration of
[0023]
This phosphorous glass is known to prevent mobile ions such as sodium from entering the semiconductor from the outside. Conventionally, the film is formed by a CVD chamber dedicated to phosphorus glass (PSG), but it requires a dedicated apparatus, which is expensive. When the present invention is used, the laser doping apparatus can be shared for impurity doping of semiconductors and phosphorous glass formation, and the silicon oxide film forming apparatus can be widely used for other applications, so that the overall cost is reduced. It is economical.
[0024]
In particular, the present invention is effective in improving the characteristics of a silicon oxide film formed at a relatively low temperature (600 ° C. or lower) using various organic silanes (tetra-ethoxy silane (TEOS), etc.) as a material. there were. That is, in such a film, a large amount of carbon in the raw material is contained, the insulating properties are poor, and when this is used as an insulating film such as a MOS structure, there are too many trap levels, It was not a good material.
[0025]
However, when phosphorous laser doping is performed according to the present invention, these carbons are removed from the film by heating with laser irradiation, trap levels are remarkably reduced, and insulating properties are improved. As already explained, the distribution of impurities in the depth direction can be controlled by changing the substrate temperature during laser doping. Therefore, to distribute phosphorus deeply in the silicon oxide film, the substrate temperature is kept at 200 ° C. or more, preferably 350 to 450 ° C., and to distribute only to a depth of 100 nm or less, the substrate is kept at room temperature or below. Just do it.
[0026]
In addition, when a semiconductor material such as amorphous silicon is present in the base during laser doping, these semiconductor materials are also annealed at the same time to improve crystallinity. That is, the silicon oxide film has a low absorptance with respect to ultraviolet rays, and a large portion of the laser light is absorbed by the underlying semiconductor material. Therefore, the two steps can be performed simultaneously, which is effective for improving mass productivity.
[0027]
A conceptual diagram of the apparatus of the present invention is shown in FIGS. FIG. 5 shows only a substrate heating device, and FIG. 6 shows an electromagnetic device for generating plasma in addition to the substrate heating device. Since these drawings are conceptual, as a matter of course, an actual apparatus may include other parts as necessary. In the following, the method of use will be outlined.
[0028]
In FIG. 5, the sample 24 is placed on the sample holder 25. First, the chamber 21 is evacuated by an exhaust system 27 connected to an exhaust device. In this case, it is desirable to exhaust as high a vacuum as possible. That is, carbon, nitrogen, and oxygen, which are atmospheric components, are generally not preferable for semiconductors. Such an element is taken into the semiconductor, but may reduce the activity of impurities added at the same time. In addition, the crystallinity of the semiconductor is impaired, and it causes a dangling bond at the grain boundary. Therefore, 10^-6less than torr, preferably 10^-8It is desirable to evacuate the chamber to below torr.
[0029]
It is also desirable to drive the heater 26 before and after exhausting to expel atmospheric components adsorbed inside the chamber. As used in the current vacuum apparatus, it is also desirable to provide a spare chamber in addition to the chamber so that the chamber does not directly touch the atmosphere. As a matter of course, it is desirable to use a turbo molecular pump or a cryopump that is less contaminated with carbon or the like than a rotary pump or an oil diffusion pump.
[0030]
When exhausted sufficiently, the reactive gas is introduced into the chamber by the gas system 28. The reactive gas may consist of a single gas, or may be diluted with hydrogen, argon, helium, neon, or the like. The pressure may be atmospheric pressure or lower. These are selected in consideration of the type of the target semiconductor, the impurity concentration, the depth of the impurity region, the substrate temperature, and the like.
[0031]
Next, the sample is irradiated with laser light 23 through the window 22. At this time, the sample is heated to a certain temperature by a heater. The laser beam is usually irradiated with about 5 to 50 pulses per location. The variation in the energy of the laser pulse is sufficiently large. Therefore, when the number of pulses is not so small, the probability of occurrence of a defect is large. On the other hand, it is not desirable from the viewpoint of mass productivity (throughput) to irradiate one place with too many pulses. According to the knowledge of the present inventor, the number of pulses described above was appropriate from the standpoints of mass productivity and yield.
[0032]
In this case, for example, when the laser pulse has a specific rectangular shape of 10 mm (x direction) × 30 mm (y direction), the same region is irradiated with 10 pulses of laser pulses. Although the method of moving to a part may be used, the laser may be moved by 1 mm in the x direction per pulse.
[0033]
When the laser irradiation is completed, the chamber is evacuated, the sample is cooled to room temperature, and the sample is taken out. Thus, in the present invention, the doping process is very simple and fast. That is, if it is a conventional ion implantation process,
(1) Doping pattern formation (resist coating, exposure, development)
(2) Ion implantation (or ion doping)
(3) Recrystallization
3 processes are required, and solid phase diffusion by conventional laser irradiation
(1) Doping pattern formation (resist application, exposure, development)
(2) Impurity film formation (spin coating, etc.)
(3) Laser irradiation
After all, three steps were necessary. However, in the present invention,
(1) Doping pattern formation (resist application, exposure, development)
(2) Laser irradiation
It is completed in two steps.
[0034]
The apparatus in FIG. 6 is almost the same as in FIG. First, the inside of the chamber 31 is evacuated by an exhaust system 37 and a reactive gas is introduced from a gas system 38. The sample 34 on the sample holder 35 is irradiated with laser light 33 through the window 32. At that time, power is applied to the electrode 39 from a high-frequency or alternating current (or direct current) power supply 40 to generate plasma or the like in the chamber to activate the reactive gas. In the drawing, the electrode is shown as a capacitive coupling type, but may be an inductive (inductance) coupling type. Further, the sample holder may be used as one electrode even if it is a capacitive coupling type. Further, the sample may be heated by the heater 36 at the time of laser irradiation.
The following examples illustrate the invention in more detail.
[0035]
【Example】
[Embodiment 1] This embodiment is an example in which the doping method which is the structure of the present invention is applied to the manufacture of an N channel thin film type insulated gate field effect transistor (hereinafter referred to as NTFT) provided on a glass substrate. In this example, a glass substrate or a quartz substrate was used as the substrate. This is because the TFT manufactured in this embodiment is intended to be used as a switching element or a driving element of an active matrix type liquid crystal display device or an easy sensor. Of course, the structure of the present invention may be applied as a doping technique for forming other semiconductor devices, for example, a P-type semiconductor layer or an N-type semiconductor layer of a photoelectric conversion device, or a single crystal semiconductor integrated circuit. . Therefore, the substrate may be silicon or other semiconductor single crystal or polycrystal, or other insulator may be used.
[0036]
First, in FIG. 1, SiO 2 is formed on a glass substrate 11 as a substrate.₂A film or a silicon nitride film is formed as the base protective film 12. In this example, SiO sputtering is performed by RF sputtering in a 100% oxygen atmosphere.₂The film 12 was formed to 200 nm. The film formation conditions are as follows.
O₂Flow rate 50sccm
Pressure 0.5pa
RF power 500W
Substrate temperature 150 degrees
[0037]
Next, a hydrogenated amorphous silicon semiconductor layer 13 having a thickness of 100 nm is formed by plasma CVD, which is intrinsic or substantially intrinsic (meaning that no impurities are artificially added). This hydrogenated amorphous silicon semiconductor layer 13 becomes a semiconductor layer constituting a channel formation region and source / drain regions. The film formation conditions are as follows.
Atmosphere Silane (SiH₄100%
Deposition temperature 160 degrees (substrate temperature)
Deposition pressure 0.05 Torr
Input power 20W (13.56MHz)
[0038]
In this embodiment, silane is used as a raw material gas for forming amorphous silicon. However, when amorphous silicon is polycrystallized by thermal crystallization, disilane is used to lower the crystallization temperature. Alternatively, trisilane may be used.
[0039]
The film forming atmosphere is made of 100% silane because the amorphous silicon film formed in a 100% silane atmosphere is compared with the amorphous silicon film formed in a silane atmosphere diluted with hydrogen. The film is based on the experimental result that it is easy to crystallize. The reason why the deposition temperature is low is that a large amount of hydrogen is contained in the deposited amorphous silicon film, and silicon bonds are neutralized with hydrogen as much as possible.
[0040]
The reason why the input power of the high-frequency energy (13.56 MHz) is as low as 20 W is to prevent the generation of silicon clusters, that is, crystalline parts as much as possible during film formation. This is also based on the experimental fact that any crystallinity in the amorphous silicon film adversely affects crystallization at the time of subsequent laser irradiation.
[0041]
Next, device separation patterning was performed to obtain the shape of FIG. Then, the sample was placed in vacuum (10^-6(Torr or less) at 450 ° C. for 1 hour, hydrogen was thoroughly discharged to form dangling bonds in the film at a high density.
[0042]
Further, the sample was transferred to the laser irradiation apparatus shown in FIG. 5 and irradiated with an excimer laser to polycrystallize the sample. In this step, a KrF excimer laser (wavelength 248 nm) was used. The conditions are as follows.
Laser irradiation energy density 350 mJ / cm²
Number of pulses 1 to 10 shots
Substrate temperature 400 degrees
After the laser irradiation, the temperature was lowered to 100 degrees in a hydrogen reduced pressure atmosphere (about 1 Torr).
[0043]
In the present embodiment, the crystallization of the amorphous silicon film by laser light irradiation is shown, but it goes without saying that this may be replaced with a heating process. This heating step is the amorphous silicon provided on the glass substrate by heating for 6 hours to 96 hours at a temperature of about 450 ° C. to 700 ° C. (generally 600 ° C.) which is lower than the heat resistant temperature of the glass. A process for crystallizing a semiconductor film.
[0044]
In FIG. 5, 21 is a vacuum chamber, 22 is a quartz window for irradiating a laser from the outside of the vacuum chamber 21 (especially, in the case of an excimer laser, anhydrous quartz is preferable), and 23 is a laser when irradiated with a laser. Light, 24 is a sample (sample), 25 is a sample holder, 26 is a heater for heating the sample, 27 is an exhaust system, 28 is a system for introducing a source gas, an inert gas or a carrier gas. Although only shown, there are actually a plurality of them. The exhaust system used a rotary pump for low vacuum and a turbo molecular pump for high vacuum, and tried to minimize the residual concentration of impurities (especially oxygen) in the chamber. 10 for exhaust capacity^-6less than torr, preferably 10^-8Torr or less.
[0045]
After crystallization with an excimer laser using the vacuum chamber of FIG. 5, SiO which becomes a gate insulating film using RF sputtering is used.₂The film 14 was formed to a thickness of 100 nm to obtain the shape shown in FIG. Then, in order to make the amorphous silicon semiconductor layer or polycrystalline silicon semiconductor layer (thickness 150 nm) to be the gate electrode 15 have an N-type conductivity type, P (phosphorus) is added. Thereafter, a gate region was formed by patterning to obtain the shape of FIG. In addition to this, a metal material such as aluminum, chromium, or tantalum may be used as the gate electrode. Further, when aluminum or tantalum is used, if the surface is anodized, the gate electrode will not be damaged during subsequent laser irradiation. Since the planar type TFT in which the gate electrode is anodized is described in Japanese Patent Application No. 3-237100 or No. 3-238713, it will not be described in detail here.
[0046]
Here, using the apparatus shown in FIG. 5 again, impurities are doped with laser light, which is the structure of the present invention. In the apparatus shown in FIG.₃In an atmosphere, a sample (having the shape shown in FIG. 3) was heated and irradiated with laser light to perform P (phosphorus) doping. At this time, since the source and drain regions (131 and 133 shown in FIG. 4) are doped with P, they are made N-type. On the other hand, the channel formation region (132 shown in FIG. 4) is not irradiated with the laser using the gate insulating film 14 and the gate electrode 15 as a mask, and the temperature of the portion does not rise, so that doping is not performed.
The doping conditions are as follows.
Atmosphere PH₃5% concentration (H₂Dilution)
Sample temperature 350 degrees
Pressure 0.02 to 1.00 Torr
Laser KrF excimer laser (wavelength 248nm)
Energy density 150-350mJ / cm²
Number of pulses 10 shots
[0047]
After the formation of the source and drain regions, as shown in FIG.₂The film 16 was formed to a thickness of 100 nm. The film forming conditions are the same as the gate oxide film manufacturing method.
[0048]
After that, hole patterning for contact is performed, and aluminum to be an electrode is vapor-deposited to form the source electrode 17 and the drain electrode 18, and hydrogen thermal annealing is performed at a temperature of 350 ° C. in a hydrogen atmosphere, whereby NTFT Was completed. Similarly, the atmosphere is B₂H₆As a result, a P-channel TFT (PTFT) could be formed.
[0049]
In particular, in order to compare the effects of the present invention, the sample was not heated at the time of laser irradiation, but was irradiated with a laser having the same intensity. However, as shown in FIG. The concentration was also one digit lower and the impurity distribution was limited to the vicinity of the surface. On the other hand, in this example, when the sample was heated to 350 ° C. and irradiated with laser, as shown in FIG. 9A, the impurity doping concentration was high, and the diffusion was deep.
[0050]
[Embodiment 2] This embodiment is an example in which the doping method according to the present invention is applied to the manufacture of NTFT provided on a glass substrate. In this example, a glass substrate or a quartz substrate was used as the substrate in the same manner as in Example 1. First, as in Example 1, SiO 2 is formed on the glass substrate 11 which is the substrate of FIG.₂A film or a silicon nitride film is formed as the base protective film 12.
[0051]
Next, an intrinsic or substantially intrinsic hydrogenated amorphous silicon semiconductor layer 13 is formed to a thickness of 100 nm by plasma CVD. Next, device separation patterning was performed to obtain the shape of FIG. Then, the sample was placed in vacuum (10^-6(Torr or less) at 450 ° C. for 1 hour, hydrogen was thoroughly discharged to form dangling bonds in the film at a high density.
[0052]
Further, the excimer laser was irradiated while maintaining the vacuum state in the chamber where the hydrogen was discharged, and the sample was polycrystallized under the same conditions as in Example 1. After the laser irradiation, the temperature was lowered to 100 degrees in a hydrogen-reduced atmosphere (about 1 Torr).
[0053]
In the present embodiment, using the apparatus shown in FIG. 6, the heating process for dehydrogenating the sample, the crystallization by excimer laser light irradiation, and the impurity doping process were performed in the same vacuum chamber. By using such a vacuum chamber, it is easy to maintain a vacuum state from the heating step to the crystallization step by laser irradiation, and a film in which no impurities (particularly oxygen) are mixed can be obtained. This vacuum chamber is provided with an electrode for applying electromagnetic energy to the atmosphere, and also serves as a PCVD apparatus. However, it goes without saying that each process may be performed in a separate reactor using an apparatus configured in a multi-chamber type. Although the reactor shown in FIG. 6 has a positive column structure, other types may be used, and the method of adding electromagnetic energy is not particularly limited. If it is desired to obtain a particularly high activation rate, it is useful to use an ECR type apparatus.
[0054]
In FIG. 6, 31 is a vacuum chamber, 32 is a quartz window for irradiating a laser from the outside of the vacuum chamber 31, 33 is a laser beam when the laser is irradiated, 34 is a sample (sample), 35 is a sample holder, Reference numeral 36 is a heater for heating the sample, 37 is an exhaust system, 38 is a system for introducing a source gas, an inert gas, or a carrier gas. Although only one is shown in the figure, a plurality is actually provided. Is. The exhaust system used a rotary pump for low vacuum and a turbo molecular pump for high vacuum, and tried to minimize the residual concentration of impurities (especially oxygen) in the chamber. Reference numeral 39 denotes a parallel plate electrode for supplying 13.56 MHz electromagnetic energy supplied from the high-frequency oscillator 40 into the chamber.
[0055]
After crystallization with an excimer laser using the vacuum chamber of FIG. 6, SiO which becomes a gate insulating film using RF sputtering is used.₂The film 14 was formed to a thickness of 100 nm to obtain the shape shown in FIG. Then, in order to make the amorphous silicon semiconductor layer or polycrystalline silicon semiconductor layer (thickness 150 nm) to be the gate electrode 15 have an N-type conductivity type, P (phosphorus) is added. Thereafter, a gate region was formed by patterning to obtain the shape of FIG.
[0056]
Here, using the apparatus shown in FIG. 6 again, doping of impurities by the laser beam which is the structure of the present invention is performed. In the apparatus shown in FIG. 6, the decomposed PH given electromagnetic energy₃In an atmosphere, a sample (having the shape shown in FIG. 3) was heated and irradiated with laser light to perform P (phosphorus) doping. At this time, since the source and drain regions (131 and 133 shown in FIG. 4) are doped with P, they are made N-type. On the other hand, the channel formation region (132 shown in FIG. 4) is not irradiated with the laser using the gate insulating film 14 and the gate electrode 15 as a mask, and the temperature of the portion does not rise, so that doping is not performed. The doping conditions are as follows.
Atmosphere PH₃5% concentration (H₂Dilution)
Sample temperature 350 degrees
Pressure 0.02 to 1.00 Torr
Input power 50-200W
Laser KrF excimer laser (wavelength 248nm)
Energy density 150-350mJ / cm²
Number of pulses 10 shots
[0057]
After the formation of the source and drain regions, as in the first embodiment, as shown in FIG.₂A film 16 is formed to a thickness of 100 nm, contact hole drilling patterning is performed, aluminum as electrodes is further deposited to form a source electrode 17 and a drain electrode 18, and a temperature of 350 ° C. in a hydrogen atmosphere. The NTFT was completed by performing hydrogen thermal annealing at
[0058]
In this doping step, the atmosphere is changed to B₂H₆As a result, a P-channel TFT (PTFT) could be formed. In the conventional case, the degree of decomposition of the doping gas differs depending on the wavelength of the laser beam, and this has caused a problem of non-uniformity in doping. As a result, the doping gas is decomposed, so that doping can be performed without being limited by the wavelength of the laser beam, regardless of whether it is a PTFT or NTFT.
[0059]
Example 3 FIG. 7 shows a state of a doping treatment apparatus of the present invention. That is, the chamber 71 is provided with a slit-like window 72 made of anhydrous quartz glass. The laser beam is formed into an elongated shape in accordance with this window. The laser beam was, for example, a 10 mm × 300 mm rectangle. The position of the laser beam is fixed. An exhaust system 77 and a gas system 78 for introducing a reactive gas are connected to the chamber. In addition, a sample holder 75 is provided in the chamber, a sample 74 is placed thereon, and an infrared lamp (functioning as a heater) 76 is provided under the sample holder. The sample holder is movable and the sample can be moved according to the laser shot.
[0060]
As described above, when a mechanism for moving the sample is incorporated in the chamber, since the sample holder is thermally distorted by the heater, the temperature is controlled carefully. Further, since dust is generated by the sample transfer mechanism, the maintenance in the chamber is troublesome.
[0061]
[Embodiment 4] FIG. 8A shows a state of a doping treatment apparatus of the present invention. That is, the chamber 81 is provided with a window 82 made of anhydrous quartz glass. Unlike the case of the third embodiment, this window is wide enough to cover the entire surface of the sample 84. An exhaust system 87 and a gas system 88 for introducing a reactive gas are connected to the chamber. In addition, a sample holder 85 is provided in the chamber, a sample 84 is placed thereon, and the sample holder has a built-in heater. The sample holder is fixed to the chamber. A chamber base 81a is provided at the lower portion of the chamber, and laser irradiation is sequentially performed by moving the entire chamber in accordance with the laser pulse. The laser beam has an elongated shape as in the third embodiment. For example, it was a rectangle of 5 mm × 100 mm. Similar to the third embodiment, the position of the laser beam is fixed. Unlike the third embodiment, this embodiment employs a mechanism that moves the entire chamber. Therefore, there is no mechanical part in the chamber, and dust and the like are not generated, so that maintenance is easy. Further, the transfer mechanism is hardly affected by the heat of the heater.
[0062]
In this embodiment, not only the above points are superior to the third embodiment, but also the following points are excellent. That is, in the system of Example 3, laser irradiation could not be performed until the sample was placed in the chamber and then evacuated to a sufficient degree of vacuum. That is, there was a lot of dead time. However, in this embodiment, if a large number of chambers as shown in FIG. 8A are prepared and rotated in order such as sample loading, vacuum evacuation, laser irradiation, and sample removal, respectively, There is no dead time. Such a system is shown in FIG.
[0063]
That is, the chambers 97 and 96 containing the unprocessed sample are directed to the gantry 99 having a stage that can be precisely moved by the continuous transport mechanism 98 during the exhaust process. The chamber 95 on the stage is irradiated with the laser beam emitted from the laser device 91 and processed by appropriate optical devices 92 and 93 through the window. The chamber 94 to which the necessary laser irradiation has been performed by moving the stage is again sent to the next stage by the continuous transport mechanism 100, during which the heater in the chamber is turned off and exhausted, and the temperature is sufficiently high. After lowering, the sample is taken out.
[0064]
As described above, in this embodiment, the continuous processing can be performed, so that the exhaust waiting time can be reduced and the throughput can be improved. Of course, in the case of the present embodiment, although the throughput is improved, more chambers are required as compared with the case of the third embodiment. Therefore, it should be performed in consideration of the mass production scale and the investment scale.
[0065]
[Embodiment 5] This embodiment is an example in which the doping method which is the configuration of the present invention is applied to manufacture of an NTFT provided on a glass substrate. In this example, a glass substrate or a quartz substrate was used as the substrate in the same manner as in Example 1. First, as in Example 1, SiO 2 is formed on the glass substrate 101 which is the substrate of FIG.₂A film is formed as a base protective film 102, and then a substantially intrinsic hydrogenated amorphous silicon semiconductor layer 103 is formed to a thickness of 100 nm by plasma CVD. Next, device separation patterning was performed. Then, the sample was placed in vacuum (10^-6(Torr or less) at 450 ° C. for 1 hour, hydrogen was thoroughly discharged to form dangling bonds in the film at a high density. Then, using RF sputtering, SiO₂A film 104 was formed to a thickness of 100 nm to obtain the shape of FIG. Then, the silicon oxide mask 105 was left only in the channel portion.
[0066]
Here, using the apparatus shown in FIG. 6, doping of impurities by laser light, which is a structure of the present invention, is performed. In the apparatus shown in FIG. 6, the decomposed PH given electromagnetic energy₃Under an atmosphere, a sample (having the shape of FIG. 10B) was heated, and laser light was irradiated to perform doping of P (phosphorus). At this time, since the source and drain regions (106 and 108 shown in the figure) are doped with P, they are made N-type. On the other hand, the channel formation region (107 shown in the figure) is irradiated with laser using the silicon oxide mask 105 as a mask and crystallized, but since the mask material exists, doping is not performed. That is, in this step, crystallization by laser and doping are performed simultaneously. The conditions at this time were the same as in Example 2.
[0067]
After the formation of the source and drain regions, a gate oxide film 110 and a gate electrode 109 are formed, and SiO 2 is used as an interlayer insulating film.₂A film 111 is formed to a thickness of 100 nm, hole patterning for contact is performed, and aluminum as an electrode is further deposited to form a source electrode 112 and a drain electrode 113, and further a temperature of 350 degrees in a hydrogen atmosphere. As shown in FIG. 10C, NTFT was completed by performing hydrogen thermal annealing.
[0068]
In this embodiment, the self-aligned source and drain cannot be formed. However, for example, if a gate electrode is formed on the gate insulating film and laser irradiation is performed from the back surface as in the first embodiment, the present embodiment As an example, the channel region can be crystallized and the source and drain can be doped simultaneously.
[0069]
Example 6 FIG. 11 shows an example in which an active matrix is formed on a Corning 7059 glass substrate. As shown in FIG. 11A, a Corning 7059 glass substrate (thickness 1.1 mm, 300 × 400 mm) was used as the substrate 201. A silicon nitride film 202 having a thickness of 5 to 50 nm, preferably 5 to 20 nm, was formed on the entire surface by plasma CVD so that impurities such as sodium contained in Corning 7059 glass would not diffuse into the TFT. As described above, a technique for coating a substrate with a silicon nitride or aluminum oxide film to form a blocking layer is described in Japanese Patent Application Nos. 3-238710 and 3-238714 filed by the present inventors. .
[0070]
Next, after forming a base oxide film 203 (silicon oxide), a silicon film 204 (thickness 30 to 150 nm, preferably 30 to 50 nm) is formed by LPCVD or plasma CVD, and further tetraethoxysilane (TEOS). As a raw material, a gate insulating film 205 (thickness 70 to 120 nm, typically 100 nm) 205 of silicon oxide was formed by plasma CVD in an oxygen atmosphere. The substrate temperature was set to 400 ° C. or lower, preferably 200 to 350 ° C. to prevent the glass from shrinking or warping. However, at such a substrate temperature, a large amount of recombination centers exist in the oxide film. For example, the interface state density is 10¹²cm^-2Thus, the gate insulating film cannot be used.
[0071]
Then, as shown in FIG. 11 (A), hydrogen diluted phosphine PH₃(5%) was irradiated with KrF laser light to improve the crystallinity of the silicon film 204 and to reduce the recombination centers (trap centers) of the gate oxide film 205. At this time, the energy density of the laser beam is 200 to 300 mJ / cm.²It was. The number of shots was also set to 10. Preferably, the temperature is kept at 200 to 400 ° C., typically 300 ° C. As a result, the crystallinity of the silicon film 204 is improved, and the gate oxide film 205 contains 1 × 10²⁰~ 3x10²⁰cm^-3Of phosphorus is doped, and the interface state density is 10¹¹cm^-2Decreased to:
[0072]
Next, as shown in FIG. 11B, an aluminum gate electrode 206 was formed, and the periphery thereof was covered with an anodic oxide 207.
[0073]
Thereafter, boron as a P-type impurity is implanted into the silicon layer by ion doping in a self-aligned manner to form TFT source / drains 208 and 209. Further, as shown in FIG. Irradiation with KrF laser light improved the crystallinity of the silicon film whose crystallinity deteriorated due to this ion doping. However, at this time, the energy density of the laser beam is 250 to 300 mJ / cm.²And set higher. Therefore, the sheet resistance of the source / drain of this TFT was 300 to 800Ω / □.
[0074]
After that, as shown in FIG. 11D, an interlayer insulator 210 was formed from polyimide, and a pixel electrode 211 was formed from ITO. Then, as shown in FIG. 11E, contact holes are formed, and electrodes 212 and 213 are formed of chromium in the source / drain regions of the TFT, and one of these electrodes 213 is also connected to ITO. did. Finally, annealing was performed in hydrogen at 300 ° C. for 2 hours to complete the hydrogenation of silicon, and a pixel of a liquid crystal display device was manufactured.
[0075]
[Embodiment 7] FIG. 11 shows an example in which a silicon oxide film is doped with phosphorus as in Embodiment 6 and a TFT is formed using this as a gate insulating film. Similarly to Example 6, a silicon nitride film 202 having a thickness of 5 to 50 nm, preferably 5 to 20 nm, was formed on the entire surface of the substrate 201 by plasma CVD as shown in FIG. Next, after forming a base oxide film 203 (silicon oxide), a silicon film 204 (thickness of 30 to 150 nm, preferably 30 to 50 nm) is formed by LPCVD or plasma CVD, and a silicon oxide film (thickness) is further formed by sputtering. 205 to 120 nm (typically 100 nm). This step may be performed by plasma CVD in an oxygen atmosphere using tetraethoxysilane (TEOS) as a raw material as in Example 6. The substrate temperature was set to 400 ° C. or less, preferably 200 to 350 ° C. in order to prevent the glass from shrinking or warping.
[0076]
Then, as shown in FIG. 11 (A), hydrogen diluted phosphine PH₃(5%) was irradiated with KrF laser light to improve the crystallinity of the silicon film 204 and to reduce the recombination centers (trap centers) of the gate oxide film 205. At this time, the energy density of the laser beam is 200 to 300 mJ / cm.²It was. The number of shots was also set to 10. The substrate temperature was room temperature. For this reason, the doping of phosphorus was limited to a portion of 70% or less from the surface of the silicon oxide film.
[0077]
Next, as shown in FIG. 11B, an aluminum gate electrode 206 was formed, and the periphery thereof was covered with an anodic oxide 207. On the contrary, a negative voltage was applied after the anodic oxidation process was completed. For example, a voltage of −100 to −200 V was applied for 0.1 to 5 hours. Preferably, the substrate temperature is 100 to 250 ° C., typically 150 ° C. By this step, mobile ions in silicon oxide or at the silicon oxide / silicon interface are attracted to the gate electrode (Al), and a region having a high concentration of phosphorus existing in the middle (presumed to be phosphorous vitrified). I was trapped. As described above, a technique for applying a negative voltage to the gate electrode after anodization or during anodization is described in Japanese Patent Application No. 4-115503 (filed on April 7, H4) of the present inventors. ing.
[0078]
Thereafter, phosphorus is implanted as a N-type impurity into the silicon layer in a self-aligned manner by a known ion doping method to form TFT source / drains 208 and 209. Further, as shown in FIG. This was irradiated with KrF laser light to improve the crystallinity of the silicon film whose crystallinity deteriorated due to this ion doping. After that, as shown in FIG. 11D, an interlayer insulator 210 was formed from polyimide, and a pixel electrode 211 was formed from ITO. Then, as shown in FIG. 11E, contact holes are formed, and electrodes 212 and 213 are formed of chromium in the source / drain regions of the TFT, and one of these electrodes 213 is also connected to ITO. did. Finally, annealing was performed in hydrogen at 300 ° C. for 2 hours to complete the hydrogenation of silicon, and a TFT was produced.
[0079]
[Embodiment 8] In this embodiment, a silicon oxide film is formed on a single crystal substrate, phosphorous laser doping is performed on the silicon oxide film, and a MOS capacitor using this as a gate oxide film is manufactured. Its characteristics (CV characteristics) Was measured.
[0080]
A gate insulating film (thickness 70 to 120 nm, typically 100 nm) of silicon oxide is formed on a single crystal silicon (100) surface by plasma CVD in an oxygen atmosphere using tetraethoxysilane (TEOS) as a raw material. Formed. The substrate temperature was 400 ° C. or lower, preferably 200 to 350 ° C. However, at such a substrate temperature, there are many clusters containing carbon in the oxide film, and there are many recombination centers. For example, the interface state density is 10¹²cm^-2Thus, the gate insulating film cannot be used.
[0081]
Therefore, using the apparatus used in Example 1, hydrogen diluted phosphine PH₃(5%) was irradiated with KrF laser light to reduce the recombination centers (trap centers) of this silicon oxide film. At this time, the energy density of the laser beam is 200 to 300 mJ / cm.²It was. The number of shots was also set to 10. Preferably, the temperature is kept at 200 to 400 ° C., typically 300 ° C. As a result, in the oxide film, 1 × 10²⁰~ 3x10²⁰cm^-3Of phosphorus is doped, and the interface state density is 10¹¹cm^-2Decreased to: Next, an aluminum gate electrode was formed.
[0082]
For example, if the laser doping process is not performed, the CV characteristic of the obtained MOS capacitor has a large hysteresis as shown in FIG. Here, the horizontal axis represents voltage, and the vertical axis represents capacitance. However, the laser doping treatment as in this example has resulted in good CV characteristics as shown in FIG.
[0083]
The distribution of each element in the film at this time is as shown in FIG. That is, phosphorus was doped partway through the silicon oxide film by laser doping in this example. Thus, it can be seen that the sodium element is gettered by this phosphorus. Further, carbon was present in a very small amount in all regions of the oxide film because it was released out of the film by laser irradiation. Also in this example, as in Example 7, when a negative voltage is applied to the gate electrode (Al), mobile ions such as sodium existing in the film are actively attracted to a region rich in phosphorus. A further effect can be obtained.
[0084]
【The invention's effect】
In the configuration of the present invention, the semiconductor is irradiated with laser light in a heated state of the sample or in an atmosphere containing an impurity imparting one conductivity type decomposed by applying electromagnetic energy to the reactive gas. It was possible to efficiently dope the impurities imparting the one conductivity type. In particular, it was possible to obtain an effect that doping can be performed without causing thermal damage to the glass substrate and without being influenced by the wavelength of the laser beam or the kind of the doping gas.
[0085]
In addition, as described above, the present invention is not limited to the purpose of doping impurities into semiconductors, but also modifies the surface of metal materials and ceramic materials, and adds trace amounts to metal thin films, ceramic thin films, and insulator thin films. It is an industrially useful invention that can be used for a wide range of purposes such as addition of elements.
[Brief description of the drawings]
FIG. 1 shows a manufacturing process of an example.
FIG. 2 shows a manufacturing process of the example.
FIG. 3 shows a manufacturing process of the example.
FIG. 4 shows a manufacturing process of the example.
FIG. 5 is a conceptual diagram of a semiconductor processing (impurity doping) apparatus according to the present invention.
FIG. 6 is a conceptual diagram of a semiconductor processing (impurity doping) apparatus according to the present invention.
FIG. 7 shows an example of a semiconductor processing (impurity doping) apparatus of the present invention.
FIG. 8 shows an example of a semiconductor processing (impurity doping) apparatus of the present invention.
FIG. 9 shows the depth distribution of impurity concentration in a semiconductor impurity region produced by the present invention and the conventional method.
FIG. 10 shows a manufacturing process of the example.
FIG. 11 shows a manufacturing process of an example.
FIG. 12 shows CV characteristics and element distribution of Examples.
[Explanation of symbols]
21 Vacuum chamber
22 Quartz window
23 Laser light
24 samples
25 Sample holder
26 Heater
27 Exhaust system
28 Gas introduction system

Claims (9)

A semiconductor film provided with first and second impurity regions and a channel formation region is provided above the substrate;
A gate insulating film containing phosphorus is provided in contact with the channel formation region;
A gate electrode is provided in contact with the gate insulating film;
An insulating film made of an organic resin is provided above the substrate, the semiconductor film, the gate insulating film, and the gate electrode,
A conductive film directly connected to the first impurity region in the first contact hole formed in the insulating film and a direct connection to the second impurity region in the second contact hole formed in the insulating film And the transmissive pixel electrode directly connected to the electrode are provided in contact with the insulating film,
The electrode is formed on and in contact with the pixel electrode, and is connected to a part of the upper surface and a part of the side surface of the pixel electrode,
The active matrix display device, wherein a connection portion between the electrode and the pixel electrode includes a portion that does not overlap with the second contact hole and does not overlap with the second impurity region. 2. The active matrix display device according to claim 1, wherein the gate electrode is provided above the channel formation region. A blocking film for blocking sodium ions is provided on the glass substrate,
A base film containing silicon oxide is provided in contact with the blocking film;
A semiconductor film provided with the first and second impurity regions and the channel formation region is provided in contact with the base film;
A gate insulating film containing phosphorus is provided on and in contact with the channel formation region;
A gate electrode is provided on and in contact with the gate insulating film;
An insulating film made of an organic resin is provided above the glass substrate, the blocking film, the base film, the semiconductor film, the gate insulating film, and the gate electrode,
A conductive film directly connected to the first impurity region in the first contact hole formed in the insulating film and a direct connection to the second impurity region in the second contact hole formed in the insulating film And the transmissive pixel electrode directly connected to the electrode are provided in contact with the insulating film,
The electrode is formed on and in contact with the pixel electrode, and is connected to a part of the upper surface and a part of the side surface of the pixel electrode,
The active matrix display device, wherein a connection portion between the electrode and the pixel electrode includes a portion that does not overlap with the second contact hole and does not overlap with the second impurity region. 4. The active matrix display device according to claim 3, wherein the blocking film contains silicon nitride or aluminum oxide. 5. The active matrix display device according to claim 1, wherein the electrode and the conductive film are made of the same material. 6. 5. The active matrix display device according to claim 1, wherein the electrode and the conductive film are made of chromium. 6. The active matrix display device according to claim 1, wherein the pixel electrode is made of ITO. In any one of claims 1 to 7, an active matrix display device, wherein the semiconductor film is a silicon film. Display device according to any one of claims 1 to 8, an active matrix display device which is a liquid crystal display device.

Images