JPH118195A - Manufacture of thin film transistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a clean interface, and to manufacture a highly efficient thin film transistor, by a method wherein, after a laser beam is applied on a semiconductor thin film in a vacuum atmosphere, the laser beam is continuously applied in an oxygen gas atmosphere. SOLUTION: A base protective film 102 of the insulating substance such as a silicon oxide film, a silicon nitride film, etc., is formed on the substrate 101 formed by ceramic material, a transparent or non-transparent substance such as fused quartz and glass, etc. After formation of a semiconductor thin film 103 on the above-mentioned base protective film 102, the substrate 101 having the semiconductor thin film 103 is set in a laser irradiation chamber 108, the chamber 108 is evacuated by an exhaust pipe 109, and a laser beam 109 is applied. Besides, oxygen gas or oxygen radical 111 is introduced into the laser irradiation chamber 108, and a laser beam is applied again in the above-mentioned state. Accordingly, an excellent MOS interface can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of manufacturing a thin film transistor formed on an insulator, a display pixel of a liquid crystal display device, or a constituent element of a liquid crystal drive circuit.

[0002]

2. Description of the Related Art Semiconductor films such as polycrystalline silicon are widely used in thin film transistors (hereinafter referred to as TFTs) and solar cells. In particular, polycrystalline silicon (poly-Si) TFTs can be formed on a transparent and insulating substrate such as a glass substrate while being able to have a high mobility, and are used for a liquid crystal display (LCD).
It is widely used as a light modulation element for LCDs and liquid crystal projectors, or as a component of a built-in driver for driving liquid crystals, and has successfully created a new market.

The performance of a TFT, which is a field-effect transistor, is naturally determined by the quality of the gate insulating film, the quality of the semiconductor film constituting the active portion thereof, and the quality of the interface between the gate insulating film and the semiconductor film. Have been. Needless to say, high quality semiconductor films, gate insulating films,
If a clean interface is obtained, a high-performance TFT corresponding to the interface can be obtained. Conversely, high performance TFTs can never be realized unless all of these requirements are met at the same time.

As a method for producing a high-performance TFT on a glass substrate, a manufacturing method called a high-temperature process has already been put to practical use. As a method of manufacturing a TFT, a process using a high temperature of about 1000 ° C. is generally called a high-temperature process. The features of the high-temperature process are that relatively high-quality poly-Si can be formed by solid-phase growth of silicon, and that a high-quality gate insulating film (generally silicon dioxide) and a clean poly-
That is, an interface between Si and the gate insulating film can be formed. Due to these characteristics in a high-temperature process, a high-performance TFT with high mobility and high reliability can be stably manufactured. However, in order to use a high-temperature process, a substrate on which a TFT is formed must be able to withstand a high-temperature heat process of 1000 ° C. or higher. Currently, the only transparent substrate that meets this condition is quartz glass. For this reason, the recent poly-S
All iTFTs are formed on a small and expensive quartz glass substrate, and are not suitable for a large size due to cost issues. In addition, the solid phase growth method requires a heat treatment for a long time of about ten hours, and there is a problem that productivity is extremely low. In addition, in this method, since the entire substrate is heated for a long time, thermal deformation of the substrate becomes a big problem, and there is a problem that it is not possible to use a substantially inexpensive large glass substrate. Also hinder cost reduction.

On the other hand, a technique called a low-temperature process is intended to solve the above-mentioned disadvantages of the high-temperature process and to realize a poly-Si TFT with high mobility. In order to use a relatively inexpensive heat-resistant glass substrate, poly-Si with a process maximum temperature of approximately 600 ° C or less
The TFT manufacturing process is generally called a low temperature process.
In the low-temperature process, a technique of crystallizing a silicon film using a pulse laser having an extremely short oscillation time is widely used. Laser crystallization is a technique that utilizes the property that an amorphous silicon film on a glass substrate is instantaneously melted by irradiating it with a high-power pulsed laser beam and then crystallized in the process of solidification. Recently, a technique of forming a large-area poly-Si film by scanning while repeatedly irradiating an amorphous silicon film on a glass substrate with an excimer laser beam has been widely used. Further, as a gate insulating film, a silicon dioxide (SiO 2) film of relatively high quality can be formed by a film forming method using plasma CVD, and the prospect of practical use can be obtained. With these technologies, po is now available on large glass substrates with
The ly-Si TFT can be formed.

However, TFTs that can be stably formed by this low-temperature process currently have a mobility of 50 to 60 (cm).
² / Vsec) or less. This is mainly because the method of forming the interface between the gate insulating film and poly-Si has not been established. At present, a process of once taking out a poly-Si film crystallized by a laser into the air and then forming a gate insulating film is generally employed. Therefore, poly must be kept clean.
An important process is how to positively control the interface between Si and the gate insulating film. For this purpose, the key point is to control the generation of surface defects by pretreatment of laser crystallization and stabilization of the surface during laser crystallization.

The following is a conventional technique for solving the above problems. First, there is a method of performing laser crystallization in a hydrogen atmosphere as disclosed in Japanese Patent Application Laid-Open No. 62-31111. This is a technique for terminating defects on the surface of poly-Si crystallized by hydrogen. However, poly-S terminated with hydrogen
The i-surface is easily oxidized and has a disadvantage that the surface state changes again before proceeding to the next step. In addition, the MOS interface terminated with hydrogen has a disadvantage that deterioration due to hot carriers during device operation becomes a problem, and reliability is impaired.

In JP-A-61-83617, oxidation is performed by simultaneously irradiating a CO2 laser and an excimer laser in an oxygen gas atmosphere. This reduces interface defects. However, when this technology is applied to poly-Si, stress due to oxidation is generated at the interface, and the device characteristics are degraded. In a process that can use high-temperature processing, this stress can be relieved by annealing at a temperature close to 1000 degrees. However, in a low-temperature process, such high-temperature annealing cannot be used, so that residual stress generates a level at the interface. .

[0009]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the present invention stabilizes the surface by pre-treatment and post-treatment of laser-crystallized poly-Si to form a clean interface. An object of the present invention is to provide a method for manufacturing a high performance thin film transistor.

[0010]

According to a first aspect of the present invention, there is provided a method of manufacturing a thin film transistor for forming an active layer by irradiating a semiconductor thin film with a laser beam and crystallizing the semiconductor thin film. After the laser beam irradiation is performed, the laser beam irradiation is continuously performed in an oxygen gas atmosphere. Here, the active layer refers to a thin film region in which the conductance of the transistor is substantially modulated to control the current flowing through the element. In addition, when laser crystallization is performed continuously in a vacuum chamber, oxygen gas is introduced into the chamber, and laser irradiation is performed again, or when the chamber is vacuum-transferred to another chamber and then replaced with an oxygen atmosphere. Say a series of processes said. That is, it means that the semiconductor thin film is not once released to the atmosphere or exposed to other gases.

According to a second aspect of the present invention, there is provided a method of manufacturing a thin film transistor for forming an active layer by irradiating a semiconductor thin film with a laser beam and crystallizing the semiconductor thin film. After that, laser beam irradiation is continuously performed in an oxygen radical atmosphere. Here, an oxygen radical refers to an oxygen molecule or an oxygen atom in a chemically active state.

According to a third aspect of the present invention, there is provided a method of manufacturing a thin film transistor according to the first or second aspect, wherein the laser beam irradiation is performed a plurality of times on the same portion.

According to a fourth aspect of the present invention, there is provided a method of manufacturing a thin film transistor according to any one of the first to third aspects, wherein the laser beam irradiation has an irradiation energy density of an energy at which a semiconductor thin film is microcrystallized. It is characterized by performing so as not to exceed.

According to a fifth aspect of the present invention, there is provided a method of manufacturing a thin film transistor according to the fourth aspect, wherein the laser beam irradiation in the oxygen gas or oxygen radical atmosphere is performed on the same portion at a maximum of 30 times. Times.

According to a sixth aspect of the present invention, there is provided a method of manufacturing a thin film transistor according to any one of the first to fifth aspects, wherein the temperature of the semiconductor thin film during laser beam irradiation in an oxygen gas or oxygen radical atmosphere is 100%. ℃ -5
It is characterized by a temperature of 00 ° C.

According to a seventh aspect of the present invention, there is provided a method of manufacturing a thin film transistor according to the first to sixth aspects, wherein the laser beam irradiation in the oxygen gas or oxygen radical atmosphere is followed by a vacuum atmosphere again. It is characterized in that a gate insulating film is continuously formed. Here, "continuously" means that after irradiating a laser in oxygen gas or oxygen radicals, these atmospheric gases are evacuated, and then a gate insulating film is formed. That is, during a series of processes from crystallization to gate insulating film formation, the atmosphere in which the semiconductor thin film is placed is not changed to the atmosphere or another gas atmosphere, and is always controlled by a vacuum or an oxygen gas or oxygen radical atmosphere. Say

In order to solve the above problem, the invention according to claim 8 is characterized in that, in the method for manufacturing a thin film transistor according to claims 1 to 7, hydrofluoric acid treatment is performed as a pretreatment of the laser irradiation. . Here, the hydrofluoric acid treatment refers to, for example, a process of immersing the semiconductor thin film substrate in a hydrofluoric acid solution.

According to a ninth aspect of the present invention, there is provided a method of manufacturing a thin film transistor for forming an active layer by irradiating a semiconductor thin film with a laser beam and crystallizing the semiconductor thin film. After the irradiation, the crystallized semiconductor film is continuously exposed to oxygen radicals.

According to a tenth aspect of the present invention, there is provided a method of manufacturing a thin film transistor according to the ninth aspect, wherein the temperature of the semiconductor film during the oxygen radical treatment is 100.
C. to 400.degree. C.

In order to solve the above-mentioned problem, the invention according to claim 11 is characterized in that, in the method for manufacturing a thin film transistor according to claims 2 to 10, the oxygen radicals are generated by remote plasma. Here, remote plasma means that the plasma generation source and the semiconductor thin film are located at different places. That is, the case where the semiconductor thin film is located between the electrodes for generating the plasma does not correspond to this.

According to a twelfth aspect of the present invention, there is provided a method of manufacturing a thin film transistor according to the eleventh aspect, wherein the remote plasma is generated by helicon wave plasma or inductively coupled plasma. .

According to a thirteenth aspect of the present invention, there is provided a method of manufacturing a thin film transistor according to the ninth to twelfth aspects, wherein a hydrofluoric acid treatment is performed as a pretreatment of the laser irradiation. .

According to a thirteenth aspect of the present invention, there is provided a method of manufacturing a thin film transistor according to the ninth to thirteenth aspects, wherein a gate insulating film is formed while maintaining a vacuum after the oxygen radical treatment. Features.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows that p
The structure of the poly-Si TFT is illustrated.

(1. Formation of Semiconductor Thin Film) In order to carry out the present invention, a base protective film (1) is usually formed on a substrate (101).
02) and a semiconductor thin film (103) are formed thereon. A series of forming methods will be described.

As shown in FIG. 1A, a substrate (101) to which the present invention can be applied includes a conductive material such as a metal,
Silicon carbide (SiC) or alumina (Al ₂ O)
₃ ) and ceramic materials such as aluminum nitride (AlN); transparent or non-transparent insulating materials such as fused quartz and glass; semiconductor materials such as silicon wafers; and LSI substrates processed from such materials. Next, FIG.
As shown in (1), a semiconductor film is deposited directly on a substrate or via a lower protective film, a lower electrode, and the like.

As the underlying protective film (102), a silicon oxide film (SiO _x : 0 <x ≦ 2) or a silicon nitride film (Si ₃ N _x :
Insulating substances such as 0 <x ≦ 4). When it is important to control impurities in a semiconductor film, such as when a thin-film semiconductor device such as a TFT is formed on a normal glass substrate, mobile ions such as sodium (Na) contained in the glass substrate are removed from the semiconductor film. It is preferable to deposit a semiconductor film after forming a base protective film so as not to mix in the semiconductor film. The same situation applies when various ceramic materials are used as the substrate. The underlayer protective film prevents impurities such as a sintering aid material added to the ceramic from diffusing and mixing into the semiconductor portion. When a conductive material such as a metal material is used as a substrate and the semiconductor film must be electrically insulated from the metal substrate, a base protective film is indispensable to ensure insulation. In addition, semiconductor substrates and LSI
When a semiconductor film is formed on an element, an interlayer insulating film between transistors and between wirings is also a base protective film.

The undercoat protective film is first washed with an organic solvent such as pure water or alcohol, and then is deposited on the substrate by atmospheric pressure chemical vapor deposition (APCVD) or low pressure chemical vapor deposition (LPCV).
D method), a CVD method such as a plasma enhanced chemical vapor deposition method (PECVD method), or a sputtering method. When a silicon oxide film is used as the base protective film, the atmospheric pressure chemical vapor deposition method can deposit the substrate using monosilane (SiH ₄ ) or oxygen as a raw material at a substrate temperature of about 250 ° C. to about 450 ° C. In the plasma chemical vapor deposition method and the sputtering method, the substrate temperature is from room temperature to about 400 ° C. The thickness of the base protective film must be sufficient to prevent diffusion and mixing of the impurity element from the substrate, and the value is at least about 100 nm or more. Considering the variation between lots and substrates, the thickness is preferably about 200 nm or more, and if it is about 300 nm, it can sufficiently function as a protective film. When the underlayer protective film also serves as an interlayer insulating film between IC elements or wiring connecting these, usually 4
The thickness is about 00 to 600 nm. If the insulating film is too thick, cracks occur in the insulating film due to stress. Therefore, the maximum thickness is preferably about 2 μm. When it is strongly necessary to consider productivity, the upper limit of the insulating film thickness is about 1 μm.

Next, as shown in FIG. 1C, a semiconductor thin film (103) is formed on the base insulating film 102. In addition to the group IV single semiconductor film such as a silicon (Si) or germanium (Ge) is the semiconductor film to which the present invention is applied, silicon germanium _{(Si x Ge 1-x:} 0 <x <1)
And silicon carbide _{(Si x C 1-x:} 0 <x <1)
And germanium carbide (Ge _x C _1-x : 0 <x <
A semiconductor film of a group 4 element composite such as 1), a composite compound semiconductor film of a group 3 element such as gallium arsenide (GaAs) or indium antimony (InSb) and a group 5 element, or cadmium selenium (CdSe) And the like. A composite compound semiconductor film of a Group 2 element and a Group 6 element, etc. Or a silicon-germanium, gallium arsenide (Si _x Ge _y Ga
_z As _z : x + y + z = 1) and further compound semiconductor films such as phosphorus (P) and arsenic (A
s), an N-type semiconductor film to which a donor element such as antimony (Sb) is added, or boron (B), aluminum (A
The present invention is also applicable to a P-type semiconductor film to which an acceptor element such as 1), gallium (Ga), and indium (In) is added. These semiconductor films are formed by APCVD or L
It is formed by a CVD method such as a PCVD method or a PECVD method, or a PVD method such as a sputtering method or an evaporation method. In the case where a silicon film is used as a semiconductor film, in the LPCVD method, the substrate temperature is set to about 400 ° C. to about 700 ° C. and disilane (S
i ₂ H ₆ ) can be deposited as a raw material. In the PECVD method, deposition can be performed at a substrate temperature of about 100 ° C. to about 500 ° C. using monosilane (SiH ₄ ) as a raw material. When using the sputter method, the substrate temperature is from room temperature to about 400 ° C. The initial state of the semiconductor film thus deposited (a
The s-deposited state) includes various states such as an amorphous state, a mixed crystal state, a microcrystalline state, and a polycrystalline state. However, in the present invention, the initial state may be any state. In the specification of the present application, not only amorphous crystallization but also polycrystalline or microcrystalline recrystallization is referred to as crystallization. The thickness of the semiconductor film is 20 when it is used for a TFT.
A thickness of about 100 nm is suitable.

(2. Laser Crystallization of Semiconductor Thin Film) After forming a base insulating film 102 and a semiconductor film 103 on a substrate 101, as shown in FIG. 1D, the semiconductor film is crystallized by laser irradiation. I do. Usually, LPCVD method,
The surface of a silicon film deposited by a CVD method such as the PECVD method is often covered with a natural oxide film. Therefore, it is necessary to remove the natural oxide film before irradiating the laser beam. For this purpose, as shown in FIG. 1D, there is a method of immersion in a hydrofluoric acid solution 104 for wet etching, a dry etching in a plasma containing fluorine gas, and the like.

Next, as shown in FIG. 1E, the substrate having the semiconductor film is set in a laser irradiation chamber (108). A part of the laser irradiation chamber is formed by a quartz window (106), and the chamber is evacuated to a vacuum by an exhaust pipe 109, and then a laser beam (107) is irradiated from the quartz window. By performing laser irradiation, the semiconductor film 103 can be crystal-grown on the p-Si film 110.

Here, the laser beam will be described. It is desired that the laser light is strongly absorbed by the surface of the semiconductor thin film (103) and hardly absorbed by the insulating film (102) immediately below. Therefore, as the laser light, an excimer laser, an argon ion laser, a YAG laser harmonic, or the like having a wavelength in or near the ultraviolet region is preferable.
Further, in order to heat the semiconductor thin film to a high temperature and to prevent damage to the substrate at the same time, it is necessary to have a large output and an extremely short pulse oscillation. Therefore, among the above laser beams, a xenon chloride (XeCl) laser (wavelength 308 nm) and krypton fluoride (Kr
F) Excimer lasers such as lasers (wavelength 248 nm) are most suitable. Next, a method for irradiating these laser beams will be described with reference to FIG. The half width of the laser pulse intensity is very short, about 10 ns to about 500 ns. The laser irradiation irradiates the substrate (200) at room temperature (25
° C) to about 400 ° C and the background vacuum is 10 ° C.
^{It is} performed in a vacuum of about ^-4 Torr to about 10 ^-9 Torr. One irradiation area of the laser irradiation has a square or rectangular shape with a diagonal of about 5 mm □ to about 60 mm □. A case where a beam that can crystallize a square area of, for example, 8 mm square by one irradiation of laser is described.
After one laser irradiation (201) is performed in one place, the position of the laser is slightly shifted relative to the substrate in the horizontal direction (203). Thereafter, one laser irradiation (202) is performed again. By continuously repeating the shot and scan, it is possible to cope with a substrate having a large area. More specifically, the irradiation area is 1% for each irradiation.
The position is shifted by about 99% (for example, 50%: 4 mm in the above example). After first scanning in the horizontal direction (X direction), then shifting in the vertical direction (Y direction) by an appropriate amount (204), scanning again in the horizontal direction by a predetermined amount (203), and thereafter repeating this scanning First laser irradiation is performed on the entire surface of the substrate. The first laser irradiation energy density ranges from about 50 mJ / cm ² to 600 mJ / cm ^2.
Between degrees is preferred. After the first laser irradiation is completed, a second laser irradiation is performed on the entire surface as necessary. When performing the second laser irradiation, the energy density is preferably higher than that of the first laser irradiation, and is 100 mJ / c.
It may be between about m ² and 1000 mJ / cm ² . The scanning method is the same as that of the first laser irradiation, and scans the square irradiation area by shifting it by an appropriate amount in the Y direction and the X direction. Further, if necessary, the third or fourth laser irradiation with a higher energy density can be performed. When such a multi-step laser irradiation method is used, it is possible to completely eliminate the variation caused by the end portion of the laser irradiation area. The laser irradiation is performed at an energy density that does not damage the semiconductor film, not only in each of the multi-stage laser irradiations but also in a normal one-step irradiation. In addition, as shown in FIG. 3, the irradiation region may be formed into a line (301) having a width of about 100 μm or more and a length of several tens of cm or more, and the linear laser light may be scanned to advance crystallization. . In this case, the overlap in the width direction of the beam for each irradiation (overlap of 301 and 302) is about 5% to about 95% of the beam width. If the beam width is 100 μm and the amount of overlap of each beam is 90%, the beam becomes 1 for each irradiation.
Since the laser beam advances by 0 μm, the same point receives laser irradiation 10 times. Normally, at least about five times of laser irradiation is desired to uniformly crystallize the semiconductor film over the entire substrate, so that the beam overlap amount for each irradiation needs to be about 80% or more. In order to reliably obtain a polycrystalline film having high crystallinity, it is preferable to adjust the overlap amount from about 90% to about 97% so that the same point is irradiated about 10 to 30 times.

(3. Laser Crystallization of Semiconductor Thin Film in Oxygen Gas or Oxygen Radical) After the entire surface crystallization is completed by the above-described process, laser crystallization in a vacuum atmosphere as shown in FIG. Oxygen gas or oxygen radical (111) is introduced into the chamber via a gas valve (105). Here, the oxygen gas is introduced into the laser crystallization chamber, for example, to a pressure approximately equal to the atmospheric pressure. However, always keep the laser crystallization chamber out of the atmosphere. That is, it is always controlled to a vacuum or an atmosphere of oxygen gas or oxygen radical. Oxygen radicals are generated by oxygen plasma or a method of flowing oxygen gas through a high-temperature filament portion. In general, since the oxygen radical has a long life, a sufficient effect can be obtained even if the oxygen radical is generated outside and introduced into the chamber through a pipe. In this way, laser light is again irradiated while the inside of the laser crystallization chamber is in an oxygen gas or oxygen radical atmosphere.

The laser beam irradiation uses exactly the same method as the shot and scan method described above. However, laser irradiation in an oxygen gas or oxygen radical atmosphere is not for crystallization, but for stabilizing defects present on the p-Si surface or grain boundaries in p-Si with oxygen atoms. Attention should be paid to the number of irradiations. By performing laser irradiation in an oxygen gas or oxygen radical atmosphere as described above, the p-Si film can be in an extremely stable state.

(4. Formation of Gate Insulating Film) Thereafter, the substrate is taken out of the laser crystallization chamber, and the p-Si film is patterned as shown in FIG. To form Thereafter, the gate insulating film 113 is formed. As a method for forming the gate insulating film, there are an ECR plasma CVD method, a parallel plate plasma CVD method, and the like. As described above, p which becomes the MOS interface
By performing a process for always protecting the surface of -Si, an extremely good semiconductor-gate insulating film structure is completed.

(5. Subsequent Steps) Subsequently, FIG.
As shown in FIG.
It is deposited by a D method or a CVD method. This material is desired to have a low electric resistance and to be stable to a heat process at about 350 ° C., for example, a high melting point metal such as tantalum, tungsten, and chromium is suitable. When the source and the drain are formed by ion doping, the thickness of the gate electrode is set to about 7 to prevent channeling of hydrogen.
About 00 nm is required. 700 among the refractory metals
Tantalum is most suitable for a material that does not cause cracks due to film stress even when formed with a film thickness of nm. After depositing a thin film to be a gate electrode, patterning is performed, and then, as shown in FIG. 1I, source / drain regions 115 are formed by implanting impurity ions into the semiconductor film. At this time, since the gate electrode serves as a mask for ion implantation, the channel has a self-aligned structure formed only under the gate electrode. Impurity ion implantation is an ion doping method in which hydride and hydrogen of an impurity element are implanted using a mass non-separable ion implanter, and an ion implantation method in which only a desired impurity element is implanted using a mass separable ion implanter. Two types of law can be applied. As a source gas for the ion doping method, a hydride of an implanted impurity element such as phosphine (PH ₃ ) or diborane (B ₂ H ₆ ) diluted in hydrogen and having a concentration of about 0.1% to about 10% is used. In the ion implantation method, only a desired impurity element is implanted, and then hydrogen ions (protons or hydrogen molecular ions) are implanted. As described above, in order to keep the MOS interface and the gate insulating film stable, the substrate temperature at the time of ion implantation should be 35 regardless of the ion doping method or the ion implantation method.
It is preferable that the temperature is 0 ° C. or lower. On the other hand, in order to constantly and stably activate the implanted impurities at a low temperature of 350 ° C. or less (this is referred to as low-temperature activation in this application), it is desirable that the substrate temperature at the time of ion implantation be 200 ° C. or more. In order to reliably activate low-concentration impurity ions at a low temperature, for example, by performing channel doping to adjust the threshold voltage of the transistor or forming an LDD structure, it is necessary to perform ion doping at the time of ion implantation. The substrate temperature must be 250 ° C. or higher. When the ion implantation is performed in such a state where the substrate temperature is high, recrystallization occurs at the same time as the crystal breakage accompanying the ion implantation of the semiconductor film, and as a result, it is possible to prevent the ion implantation portion from becoming amorphous. It is. That is, the ion-implanted region remains crystalline after the implantation, and the implanted ions can be activated even if the subsequent activation temperature is as low as about 350 ° C. or less. CMOS TFT
Is formed, one of the NMOS and the PMOS is alternately covered with a mask using an appropriate mask material such as a polyimide resin, and the respective ions are implanted by the above-described method.

After forming the source and drain, an interlayer insulating film 116 is formed as shown in FIG.
As shown in (k), a contact hole is formed on the source / drain, and the source / drain extraction electrode 1 is formed.
17 and wiring are formed by a PVD method, a CVD method, or the like to complete a thin film transistor.

[Embodiment] An embodiment of the present invention will be described with reference to FIG. The substrate and the underlying protective film used in the present invention follow the above description, but as shown in FIG. 4A, here, a 300 mm × 300 mm square general-purpose alkali-free glass 401 is used as an example of the substrate. FIG. 4 (b)
As shown in FIG. 1, first, a base protective film 402, which is an insulating material, is formed on a substrate 401. Here, the substrate temperature is set to 1
A silicon oxide film having a thickness of about 200 nm is deposited by ECR-PECVD at 50 ° C. Next, FIG.
As shown in (c), a semiconductor film 403 such as an intrinsic silicon film which will be an active layer of the thin film transistor later is deposited. The thickness of the semiconductor film is about 50 nm. In this example, the amorphous silicon film 403 is deposited at a deposition temperature of 425 ° C. by flowing disilane (Si ₂ H ₆ ) as a source gas at 200 SCCM using a high vacuum LPCVD apparatus. First, a plurality of (for example, 17) substrates are placed inside a reaction chamber of a high-vacuum LPCVD apparatus with the reaction chamber at 250 ° C., with the front side facing down. After this, the operation of the turbo-molecular pump is started. After the turbo molecular pump reaches a steady rotation, the temperature in the reaction chamber is increased from 250 ° C. to 42
Raise to a deposition temperature of 5 ° C. First one after starting heating
During 0 minutes, the temperature is raised in a vacuum without introducing any gas into the reaction chamber, and thereafter nitrogen gas having a purity of 99.9999% or more is continuously flowed at 300 SCCM. At this time, the equilibrium pressure in the reaction chamber is 3.0 × 10 ⁻³ Torr. After reaching the deposition temperature, disilane (Si
₂ H ₆ ) was run at 200 SCCM and the purity was 99.9.
Helium (He) for dilution of 999% or more at 1000 SC
Run the CM. The pressure in the reaction chamber immediately after the start of the deposition was about 0.85
Torr. As the deposition proceeds, the pressure in the reaction chamber gradually increases, and the pressure immediately before the end of the deposition is approximately 1.25 Torr.
r. The silicon film 403 deposited in this manner has a region of 286 mm square except for a peripheral portion of about 7 mm of the substrate.
The thickness variation is within ± 5%.

After the formation of the amorphous silicon film, as shown in FIG. 4D, it is immersed in a hydrofluoric acid solution 404, and the natural oxide film on the semiconductor film 403 is etched. Generally, the surface where the silicon film is exposed is very unstable, and easily reacts with the atmospheric substance holding the silicon thin film. Therefore, it is necessary to not only remove the natural oxide film but also to stabilize the exposed surface of the silicon film in the pretreatment for performing the laser irradiation. For this purpose, treatment with a hydrofluoric acid solution is desirable. The mixing ratio of hydrofluoric acid with pure water is adjusted to 1:30. Immediately after immersion in this hydrofluoric acid solution for about 20 to 30 seconds, washing with pure water is performed for 10 to 20 minutes. Thereafter, pure water is removed with a spinner. As a result, the silicon film surface becomes a stabilized surface terminated with hydrogen atoms. If this step is not performed, the state of the silicon film surface at the time of laser irradiation will not be controlled at all, and the effect of laser irradiation that controls the atmosphere, which will be described later, will not be obtained. Therefore, in the present application, this hydrofluoric acid cleaning process is indispensable.

Next, as shown in FIG. 4E, irradiation with laser light 407 is performed. In this example, xenon chloride (XeCl) excimer laser (wavelength: 30)
8 nm). The half width of the laser pulse intensity (half width with respect to time) is 45 ns. After the substrate 401 is set in the laser crystallization chamber 408 at room temperature (25 ° C.), vacuum exhaust is performed through the exhaust pipe 405.
The crystallinity of the p-Si film 410 can be improved by irradiating the substrate 401 with a laser beam 407 through a quartz window 406 while heating the substrate 401, so that the substrate temperature is increased to 400 ° C. after evacuation. One laser irradiation area is a square shape of 8 mm square, and the energy density on the irradiation surface is 160 mJ / cm ² . This laser beam is overlapped by 90% (that is, 0.8 mm for each irradiation)
The irradiation is repeated while being relatively shifted (see FIG. 2). Thus, the amorphous silicon on the entire substrate having a side of 300 mm is crystallized. A second laser irradiation is performed using a similar irradiation method. The second energy density is 1
It is 80 mJ / cm ² . Repeat this for the third time, 4
While increasing the irradiation energy density by about 20 mJ / cm ² each time, the final energy density was 300 mJ / cm ^2.
Irradiation of cm ² is performed and laser irradiation is completed. Irradiation with a high energy exceeding the irradiation laser energy density of 300 mJ / cm ² causes microcrystallization of the p-Si grains, so that further energy irradiation was avoided.

Next, as shown in FIG. 4F, oxygen gas or oxygen radicals 411 are introduced into the laser crystallization chamber 408. In this example, 99.999% oxygen gas was introduced from the gas valve 405 to about 1 atm. In this state, excimer laser irradiation is performed through a quartz window 406. The laser irradiation is performed by scanning in the same manner as the laser irradiation in a vacuum. At this time, the overlap ratio of the beam was 90%, and the irradiation laser energy was 300 mJ.
/ Cm ² . By performing laser irradiation in a vacuum, hydrogen atoms that initially covered the silicon film surface are eliminated. Typically, hydrogen bonded to silicon is 400
It desorbs at a temperature of around 620C or around 620C. Since the p-Si film that has been subjected to laser irradiation a plurality of times has a temperature of 1000 ° C. or higher, its surface hydrogen is completely eliminated. Therefore, the surface silicon atoms forming the dangling bonds exist in a vacuum in an extremely active state. If this is taken out to the atmosphere as it is, it is instantaneously bonded to carbon or water in the atmosphere, and this eventually results in remaining at the MOS interface of the p-Si TFT. Normally, treatment with hydrofluoric acid or the like is performed after laser crystallization, but the silicon surface once bonded to impurities does not change by acid cleaning. In order to prevent this, it has been found that laser irradiation in an oxygen gas atmosphere following laser crystallization is extremely effective. Other types of gases have been tried, but oxygen gas is the most effective. This is because the extremely activated silicon film surface, crystal grain boundaries, and the like are stabilized again by oxygen atoms by laser irradiation in oxygen gas. It has been found that at least a plurality of laser irradiations are required to terminate defects with oxygen. In addition, it was found that the irradiation energy had to be weaker than the energy region of microcrystallization described above, so that the irradiation energy density was 30 here.
0 mJ / cm ² . Irradiation with this energy is 30
It has been found that if the number of times exceeds this, the surface of the p-Si becomes rough and the number of surface defects increases. Therefore, it is preferable that the laser irradiation in an oxygen atmosphere be performed less than 30 times in one place. .

Further, instead of irradiating a laser in oxygen gas or oxygen radicals, a method of simply introducing oxygen radicals into a laser-crystallized p-Si film is also effective. Since oxygen radicals have a long life, a substance generated by an external plasma source is introduced through a gas valve 411 through a pipe. Examples of the oxygen radical generating source include a helicon wave plasma combining a helical antenna and a magnetic field, and an inductively coupled plasma using an antenna having a small number of turns. Since these plasmas have a low discharge voltage, the lifetime of oxygen radicals is longer than that of other plasma generation methods, and it has been found that these plasmas are the most suitable plasma generation sources for achieving the object of the present invention.
In addition, since oxygen radicals can be generated at a low pressure, it was found that the radical stabilization effect in the substrate was extremely uniform even though the radicals were supplied from a pipe.
Also, it has been found that when stabilizing the p-Si surface with oxygen radicals, the substrate temperature is preferably about 100 ° C to 400 ° C. Thereby, stabilization in a relatively short time became possible.

Next, as shown in FIG. 4G, the laser crystallization chamber is evacuated again, and the substrate is transferred to the gate insulating film formation chamber while maintaining the vacuum.
Here, the gate insulating film 413 is formed by a CVD method, a PVD method, or the like. In this example, a 120 nm silicon oxide film is deposited by applying rf to the parallel plate electrode 419 at a substrate temperature of 350 ° C. by a parallel plate rf discharge PECVD method. TEOS (Si— (O—CH ₂ —
A mixed gas 418 of CH ₃ ) ₄ ) and oxygen (O ₂ ) was used. The p-Si surface once stabilized with oxygen is quite stable, and a patterning process may be performed before forming the gate insulating film as shown in FIG. 1, but the gate insulating film is continuously formed to form a cleaner interface. It was found that forming a film had the effect.

Subsequently, as shown in FIG.
A thin film serving as the gate electrode 414 is deposited by a PVD method, a CVD method, or the like. Usually, the gate electrode and the gate wiring are made of the same material in the same process, so that this material is desired to have low electric resistance and to be stable to a heat process of about 350 ° C. In this example, a tantalum thin film having a thickness of 600 nm is formed by a sputtering method. The substrate temperature for forming the tantalum thin film is 180 ° C., and an argon gas containing 6.7% of a nitrogen gas is used as a sputtering gas. The thus formed tantalum thin film has an α-structure crystal structure, and its specific resistance is approximately 40 μΩcm. After depositing a thin film to be a gate electrode, patterning is performed, and subsequently, FIG.
As shown in (1), a source / drain region 415 and a channel region are formed by implanting impurity ions into the semiconductor film. At this time, since the gate electrode serves as a mask for ion implantation, the channel has a self-aligned structure formed only under the gate electrode. As a source gas for the ion doping method, a concentration of about 0.1% diluted in hydrogen to about 10% is used.
% Of a hydride of an implanted impurity element such as phosphine (PH ₃ ) or diborane (B ₂ H ₆ ). In this example, NMO
In order to form S, phosphine (PH ₃ ) having a concentration of 5% diluted in hydrogen is injected at an acceleration voltage of 100 keV using an ion doping apparatus. The total ion implantation amount including PH ₃ ⁺ and H ₂ ⁺ ions is 1 × 10 ¹⁶ cm ⁻² .

Next, as shown in FIG. 4K, an interlayer insulating film 416 is formed by a CVD method or a PVD method. In this example, TEOS (Si— (O—CH ₂ —CH ₃ ) ₄ ), oxygen (O ₂ ), and water (H ₂ O) are used as source gases, and argon is used as a diluent gas, and the substrate surface temperature is 500 ° C. at 300 ° C. To a film thickness of After ion implantation and interlayer insulating film formation, 35
A heat treatment for several tens minutes to several hours is performed in an appropriate thermal environment of about 0 ° C. or less to activate the implanted ions and bake the interlayer insulating film. This heat treatment temperature is preferably about 250 ° C. or more in order to surely activate the implanted ions. In order to effectively bake the interlayer insulating film, a temperature of 300 ° C. or more is preferable. Normally, the film quality of the gate insulating film differs from that of the interlayer insulating film. Therefore, when contact holes are opened in the two insulating films after the formation of the interlayer insulating film, the etching rates of the insulating films are usually different. Under such conditions, the shape of the contact hole becomes inversely tapered as it goes downward, or an eave is formed, and the contact hole is cut off, which causes a so-called poor contact in which electrical conduction cannot be taken well when the electrode is formed. By effectively baking the interlayer insulating film, the occurrence of such contact failure can be minimized. In this example, heat treatment is performed at 300 ° C. for one hour under an atmosphere of oxygen containing steam having a dew point of 80 ° C. and 1 atm. Compared to simple heat treatment,
In an oxygen-containing gas atmosphere containing water vapor at a dew point of about 35 ° C. to about 100 ° C. (oxygen concentration is preferably about 25% to 100%), the pressure is set to about 0.5 to 1.5 atm. When the heat treatment is performed at a temperature of about 400 ° C. for about 30 minutes to about 6 hours, the quality of the oxide film (underlying protective film, gate insulating film, interlayer insulating film, etc.) is improved,
A highly reliable transistor which operates stably even under a high voltage or a high current can be obtained. After the formation of the interlayer insulating film, as shown in FIG. 4 (l), a contact hole is formed on the source / drain, and a source / drain extraction electrode 417 and a wiring are formed by a PVD method, a CVD method, or the like to complete a thin film transistor. I do.

As described above, according to the present invention, even if an inexpensive general-purpose glass substrate is used, an excellent MOS interface can be formed by stabilizing the film surface after laser crystallization using oxygen. This technology can be realized, and by applying this technology, high-performance thin film semiconductor devices such as thin film transistors and solar cells can be manufactured.

[Brief description of the drawings]

FIG. 1 is a process sectional view showing a method for manufacturing a thin film transistor of the present invention.

FIG. 2 shows a laser beam irradiation method during laser crystallization.

FIG. 3 shows a laser beam irradiation method during laser crystallization.

FIG. 4 is a process sectional view illustrating the method for manufacturing the thin film transistor of the present invention.

[Explanation of symbols]

 101. . . Substrate 102. . . Base insulating film 103. . . Semiconductor film 104. . . Insulating film 106. . . Quartz window 107. . . Laser light 110. . . Crystallized semiconductor film 111. . . Oxygen gas or oxygen radical109. . . Exhaust pipe 113. . . Gate insulating film 114. . . Gate electrode 115. . . Source / drain region 116. . . Interlayer insulating film 117. . . Source and drain electrodes

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01L 29/78 627F

Claims (14)

[Claims] 1. A method for manufacturing a thin film transistor, wherein an active layer is formed by irradiating a semiconductor thin film with a laser beam to crystallize the semiconductor thin film. A method for manufacturing a thin film transistor, comprising performing beam irradiation. 2. A method of manufacturing a thin film transistor, wherein an active layer is formed by irradiating a semiconductor thin film with a laser beam to crystallize the semiconductor thin film. A method for manufacturing a thin film transistor, comprising performing beam irradiation. 3. The method according to claim 1, wherein the laser beam irradiation is performed a plurality of times on the same portion. 4. The laser beam irradiation according to claim 1, wherein the irradiation energy density does not exceed the energy at which the semiconductor thin film causes microcrystallization.
4. The method for manufacturing a thin film transistor according to 3. 5. The laser beam irradiation in the oxygen gas or oxygen radical atmosphere is performed at a maximum of 3 times on the same location.
5. The method according to claim 4, wherein the number of times is zero. 6. A semiconductor thin-film temperature of 100 ° C. when irradiating a laser beam in an oxygen gas or oxygen radical atmosphere.
The method for producing a thin film transistor according to claim 1, wherein the temperature is in the range of −500 ° C. 7. The method of manufacturing a thin film transistor according to claim 1, wherein after the laser beam irradiation in the oxygen gas or oxygen radical atmosphere, the vacuum atmosphere is again established and the gate insulating film is continuously formed. Method. 8. The method for manufacturing a thin film transistor according to claim 1, wherein a hydrofluoric acid treatment is performed as a pretreatment for said laser irradiation. 9. A method of manufacturing a thin film transistor in which an active layer is formed by irradiating a semiconductor thin film with a laser beam to crystallize the semiconductor thin film, wherein the laser beam is first irradiated in a vacuum and then crystallized into oxygen radicals. A method for manufacturing a thin film transistor, comprising exposing a semiconductor film. 10. The semiconductor film temperature during the oxygen radical treatment is 100 ° C. to 400 ° C.
A method for manufacturing the thin film transistor according to the above. 11. The apparatus according to claim 2, wherein said oxygen radicals are generated by remote plasma.
A method for manufacturing the thin film transistor according to the above. 12. The method according to claim 11, wherein said remote plasma is generated by helicon wave plasma or inductively coupled plasma. 13. A method according to claim 9, wherein a hydrofluoric acid treatment is performed as a pretreatment for said laser irradiation.
A method for manufacturing the thin film transistor according to the above. 14. The method of manufacturing a thin film transistor according to claim 9, wherein, after said oxygen radical treatment, a gate insulating film is formed while maintaining a vacuum.