JP3024543B2 - Crystalline silicon film and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystalline silicon film used as a material for a TFT (thin film transistor) switch provided in each pixel of a liquid crystal display device, used for an integrated circuit, a solar cell, and the like. The present invention relates to a method for forming a crystalline silicon film.

[0002]

2. Description of the Related Art Conventionally, as a method for forming a crystalline silicon film, a CVD method, particularly a thermal CVD method, has been frequently used. CV
In order to form a crystalline silicon film by the method D, it is usually necessary to maintain the temperature of the article on which the film is to be formed at about 800 ° C. or higher. In addition, a PVD method such as a vacuum evaporation method and a sputter evaporation method is also used. In this case, too, in order to make the film have crystallinity, usually, the temperature of the article to be formed is set to 700 ° C.
It needs to be kept above a certain degree.

In recent years, after forming an amorphous silicon film at a relatively low temperature by various CVD methods and PVD methods, as a post-treatment, a heat treatment at about 800 ° C. or more or a long time at about 600 ° C. for about 20 hours or more. Heat treatment or laser annealing is performed to convert the film into a crystalline silicon film.

[0004]

However, as described above, depending on the method of forming a crystalline silicon film directly by various CVD methods and PVD methods, for example, a relatively inexpensive low melting point glass is used as a glass substrate of a liquid crystal display device. Using
When a crystalline silicon film is to be formed to form a TFT on this substrate, the low melting glass is
If the temperature is kept at ℃ or 800 ° C., melting or distortion occurs. As described above, it is difficult to form a crystalline silicon film directly on an article made of a material having relatively low heat resistance by the method of directly forming a crystalline silicon film by the CVD method or the PVD method.

In addition, the method of obtaining a crystalline silicon film by performing the above-described heat treatment or laser annealing as a post-process has one step more than the method of directly forming a crystalline silicon film, and thus has a low productivity. In addition, the laser annealing process has a disadvantage that a laser irradiation device is expensive and a film having a large area and good uniformity cannot be obtained. Therefore, an object of the present invention is to provide a crystalline silicon film formed at a relatively low temperature with high productivity and a method for forming a crystalline silicon film capable of forming a film with a high productivity at relatively low temperature. .

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method in which a raw material gas containing a silicon-based gas is turned into plasma by supplying plasma excitation energy and formed on a film-forming article under the plasma. A crystalline silicon film, wherein the film comprises an interface layer with the article to be deposited and an upper layer film, and the interface layer reduces the degree of vacuum in the vicinity of the article surface to 1 × 10 ^−3.
A layer in which the surface of the article is exposed to the plasma while maintaining the pressure at Torr to 1 × 10 ⁻⁸ Torr, and the surface of the article is irradiated with an ion beam to form silicon crystal seeds. Degree of vacuum near 1 × 10 ^-3
A crystalline silicon film characterized by being a layer in which a silicon crystal is grown without irradiating an ion beam by exposing the surface of the article to the plasma while maintaining the pressure at Torr to 1 × 10 ⁻⁸ Torr.

According to another aspect of the present invention, a raw material gas containing a silicon-based gas is converted into a plasma by supplying energy for plasma excitation, and a film-forming article is exposed to the plasma to form a crystalline film on the article. A method of forming a silicon film, wherein the degree of vacuum near the surface of the article is 1 × 10 ⁻³ To
After exposing the surface of the article to the plasma while maintaining the rr to 1 × 10 ⁻⁸ Torr and irradiating the surface of the article with an ion beam to form an interface layer containing silicon crystal seeds on the article, ion beam irradiation is performed. Is stopped, and the degree of vacuum in the vicinity of the surface of the article is continuously reduced to 1 × 10 ⁻³ Torr to 1 × 10 ⁻⁸ To.
A method for forming a crystalline silicon film, characterized in that the surface of the article is exposed to the plasma while maintaining rr to form an upper layer film of crystalline silicon.

In the crystalline silicon film and the method for forming a crystalline silicon film according to the present invention, the neutral particles having neutralized energy may be irradiated together with the ion beam irradiation. . According to the crystalline silicon film and the method for forming a crystalline silicon film of the present invention,
A source gas containing a silicon-based gas is converted into plasma, and in forming a crystalline silicon film under this plasma, an ion beam is used in combination to form an interface layer, and then the ion beam is stopped and the source of the plasma is continuously applied. In order to form an upper layer film, a crystal seed (a seed for crystallizing silicon) can be formed in the interface layer. In addition, when forming an upper layer film used for an actual device, It is possible to promote the growth of a high-quality silicon crystal in a state where excessive damage and contamination of impurities due to ion beam irradiation on the silicon growth surface are avoided.

Further, since it is sufficient to operate the ion source only at the initial stage of film formation, it is possible to save energy and reduce the number of maintenance operations of the ion source. Since the ion source may be operated, the influence of the operation and control of the ion source on other control systems of the film forming apparatus can be reduced, and the stability of the entire film forming apparatus can be improved.

The degree of vacuum in the vicinity of the surface of the article is 1 ×
By applying a high degree of vacuum (low pressure) of 10 ⁻³ Torr to 1 × 10 ⁻⁸ Torr, the surface of the article can be irradiated with an ion beam, and the ion species and ion acceleration energy can be appropriately selected or adjusted. By surface excitation,
Effects such as control of crystallinity, control of crystal grain size, control of crystal orientation, etc. are obtained, and migration or migration of silicon atoms (migra
) is promoted, and a silicon film having better crystallinity can be formed on the article to be formed. In the case of plasma CVD, the energy of reactive species due to plasma excitation covers a wide range of several eV to several hundred eV.
It is difficult to perform such control by simple plasma CVD.

Further, 1 × 10 ⁻³ Torr to 1 × 10 ⁻⁸ T
Since the gas is converted into plasma under a high degree of vacuum of orr, the gas phase reaction is suppressed, the generation of unnecessary dust particles is reduced, the adhesion of impurities to the surface of the article to be formed is suppressed, and the crystallinity is further improved. A silicon film is obtained. Further, since the gas is converted into plasma under a high vacuum, a diffusion region of radicals contributing to film formation is widened, so that a high-quality crystalline silicon film can be formed on an article to be formed having a large area. Further, the film is less attached to the inner surface of the container where the film is formed in the crystalline silicon film forming step, and maintenance such as cleaning becomes easier accordingly.

According to the method of the present invention, silicon can be crystallized at a relatively low temperature. In addition, since a silicon film having such crystallinity can be obtained in one step, heat treatment after film formation can be omitted, and productivity is good. Further, in the crystalline silicon film and the method for forming a crystalline silicon film according to the present invention, as the ion species of the ion beam, an inert gas (helium (He) gas, neon (Ne) gas, argon (Ar) gas, krypton (Kr) gas, xenon (Xe) gas, etc.), reactive gas (hydrogen (H ₂ ) gas, fluorine (F ₂ ) gas, hydrogen fluoride (HF) gas, etc.) and silicon-based gas (monosilane (S
iH ₄₎ gas, disilane (Si ₂ H ₆₎ silicon hydride gas such as a gas, silicon tetrafluoride (SiF ₄₎ silicon fluoride gas such as a gas, silicon tetrachloride (SiCl ₄₎ silicon chloride gas such as a gas, such as )), Ions of at least one gas can be used.

When irradiating with the inert gas ions, physical excitation control for crystallization can be performed. When the reactive gas and the silicon-based gas containing hydrogen (H) or (and) fluorine (F) are used, hydrogen atoms and fluorine atoms are bonded to silicon atoms in the amorphous phase in the film. This is vaporized, crystallization of silicon is promoted, and dangling bonds and defects in the film in the silicon-silicon network are reduced.
A silicon film having higher crystallinity can be formed.

In the crystalline silicon film and the method for forming a crystalline silicon film according to the present invention, it is conceivable that the article to be formed is irradiated with the ion beam at a low energy of about 100 eV to 1 keV. A silicon film having higher quality crystallinity can be formed without hindering effects such as surface excitation, crystallinity improvement, and crystal orientation control by irradiating an ion beam to a film-formed article.

Further, in the crystalline silicon film and the method of forming a crystalline silicon film according to the present invention, at least one of the silicon-based gases exemplified as the gas serving as the ion source of the ion beam as the source gas for the plasma. Or at least one of the silicon-based gases and at least one of the reactive gases.

Since the ion source gas diffuses from the ion source into the container where the film is formed, when a silicon-based gas is used as the ion source gas used for ion beam irradiation, silicon gas is separately used as the plasma source gas. In some cases, introduction of the system gas into the film forming container can be omitted. Further, in the crystalline silicon film and the method for forming a crystalline silicon film of the present invention, the temperature of the article to be formed can be set at room temperature to 600 ° C. A silicon film having properties can be obtained. When the temperature is lower than room temperature, an amorphous component increases in the formed silicon film, and the crystallinity decreases.

Further, when it is necessary to further improve the crystallinity, it is conceivable to perform a heat treatment at 300 ° C. to 600 ° C. on the crystalline silicon film as a post-treatment after the film formation. The hydrogen concentration in the silicon film obtained by the method of the present invention can be set to 1 × 10 ²¹ cm ⁻³ or less, which is about two orders of magnitude lower than that of the silicon film obtained by the ordinary CVD method. By the treatment, a silicon film with less voids and higher quality crystallinity can be formed. In addition, even when performing post-treatment, the heating temperature can be lower than in the conventional post-treatment performed for crystallization, and the heating time can be shortened.

In the crystalline silicon film and the method for forming a crystalline silicon film according to the present invention, high-frequency power, microwave power, light, or the like can be used as the energy for plasma excitation. In the crystalline silicon film of the present invention, it is conceivable that the thickness of the interface layer is about 50 ° to 1000 °. When the thickness of the interface layer is smaller than 50 °, the crystal grain size and crystallinity greatly change with a slight change in the thickness of the interface layer, so that it is difficult to control the film quality to be constant. Further, since the thickness of the crystalline silicon film usually used for a TFT device or the like is about 1000 °, it is conceivable that the thickness of the interface layer is also reduced to about 1000 °.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of an example of a film forming apparatus that can be used for carrying out the method of the present invention. This apparatus has a film forming chamber 1, and a high-frequency electrode 2 and a ground electrode 3 are installed at positions facing each other in the chamber 1. A high frequency power supply 22 is connected to the electrode 2 via a matching unit 21. The electrode 3 also serves as a holder for supporting the article S on which a film is to be formed, and has a heater 31 for heating the article therein. In the film forming chamber 1, an article holder 3 is provided.
The ion source 4 is installed at a position where the film-forming article S supported by the apparatus can be irradiated with ions. Further, the film forming chamber 1 is connected to a vacuum exhaust unit 5 and a plasma source gas supply unit 6. The source gas supply section 6 includes a plasma source gas source, a mass flow controller, and the like, but these are not shown.

In forming the crystalline silicon film of the present invention using this apparatus, the article S to be deposited is loaded into the deposition chamber 1 and supported by the holder 3, and then the operation of the vacuum exhaust unit 5 is performed. The inside of the chamber 1 is set to a predetermined degree of vacuum. Next, the raw material gas is introduced into the chamber 1 from the gas supply unit 6 and the electrode 2
A high-frequency power is applied from a power source 22 to a plasma through a matching unit 21 to convert the gas into plasma.
Irradiate at 0 eV to 1 keV, and under this plasma the article S
An interface layer containing a silicon crystal seed is formed on the surface. In addition,
The thickness of the interface layer is 100 to 1000 °.

Then, the irradiation of the ion beam from the ion source 4 is stopped, and only the source gas is turned into plasma by applying high-frequency power to form an upper layer of the crystalline silicon film on the formed interface layer. During the film formation, the degree of vacuum in the vicinity of the surface of the article S is 1 × 10 ⁻³ Torr to 1 × 1.
The degree of vacuum in the film forming chamber 1 is adjusted so as to fall within the range of 0 ^-8 Torr. Further, the temperature of the article S to be film-formed is set to a range from room temperature to 600 ° C.
Keep at ° C. In this way, an upper layer film is formed by growing silicon crystals on the interface layer containing the formed silicon crystal seeds.

By the above operation, as shown in FIG. 2, the crystalline silicon film M composed of the interface layer M1 and the upper film M2 is formed on the article S to be formed. According to the above-described method and the crystalline silicon film obtained by this, a crystal seed of silicon is formed in the interface layer M1 by the action of the ion beam, and the upper film M2 used in an actual device is formed.
In the state where the film is not damaged by ion irradiation and impurities are not mixed, crystallization is promoted by crystal seeds in the interface layer M1,
A silicon film having good crystallinity is obtained.

In forming the interface layer, the article S is irradiated with an ion beam, and the irradiation energy is controlled to a low level of 1 keV or less, so that the surface is excited by the ion beam, the crystallinity is improved, and the crystal orientation is controlled. Such effects are not hindered, migration of silicon atoms is promoted, and the silicon film M has higher crystallinity.

Further, during the film formation, silicon can be crystallized without setting the temperature of the article S higher than 600 ° C. For this reason, for example, an inexpensive glass having a relatively low melting point is used as a glass substrate for a liquid crystal display device, and T
A silicon film for FT or the like can be formed. In addition, since a crystalline silicon film can be obtained in one step, heat treatment after film formation can be omitted, and productivity is good. Even if heat treatment is applied because it is necessary to further improve crystallinity,
The temperature is lower than the conventional temperature of 300 ° C. to 600 ° C., and the heating time can be shorter than the conventional one (20 hours or more).

Further, 1 × 10 ⁻³ Torr to 1 × 10 ⁻⁸ T
Since the raw material gas is converted into plasma under a high degree of vacuum of orr, the gas phase reaction is suppressed, the generation of unnecessary particles is suppressed, and the adhesion of impurities to the article S to be formed is suppressed, so that better crystallinity is obtained. A silicon film is obtained. In addition, since the source gas is turned into plasma under high vacuum as described above, the diffusion region of radicals contributing to film formation is widened, and a high-quality crystalline silicon film is formed on a large-area article S to be formed. be able to. Further, film deposition on the inner surface of the film forming chamber 1 and the like is small, so that the frequency of cleaning the inside of the chamber 1 can be reduced.

Since the ion source 4 only needs to be operated only at the initial stage of film formation, energy can be saved, the number of maintenance operations of the ion source 4 can be reduced, and the ion source 4 can be used only at the initial stage of film formation. Since the ion source 4 only needs to be operated, the influence of the operation of the ion source 4 on the control system in other parts of the film forming apparatus can be reduced, and the stability of the entire film forming apparatus can be improved.

Next, a specific example of forming a crystalline silicon film by the method of the present invention using the apparatus shown in FIG. 1 and an example of the crystalline silicon film of the present invention obtained as a result will be described. In addition, a comparative example in which a silicon film is formed using a conventional parallel plate type plasma CVD apparatus will be described. Example 1-deposition target article non-alkali glass substrate and respectively, the film formation conditions of the silicon wafer <100><interfacial layer formation> plasma excitation power ₄ 50% frequency 13.56MHz high-frequency power source gas SiH H ₂ 50% Degree of vacuum 1 × 10 ⁻⁴ Torr Ion beam ion species Ion of mixed gas of SiH ₄ and H ₂ Irradiation energy of 100 eV and 1 keV respectively Deposition temperature 300 ° C. Deposition film thickness 10 to 1000Å <Formation of upper layer film> Power for plasma excitation High frequency power of frequency 13.56 MHz Source gas SiH ₄ 50% H ₂ 50% Vacuum degree 1 × 10 ^-4 Torr Film forming temperature 300 ° C. ・ Total film thickness 2500 ° Comparative Example ・ Articles to be formed Non-alkali glass substrate and silicon wafer <100> Each of the film formation conditions Plasma excitation power High frequency power at a frequency of 13.56 MHz Source gas SiH ₄ 50% H ₂ 50% Vacuum degree 2 × 10 ⁻¹ Torr Film forming temperature 300 ° C. Film thickness 2000 ° Next, the X-rays were obtained for each of the silicon films obtained by the above-mentioned Examples of the present invention and Comparative Examples. Crystallinity was evaluated by diffraction analysis (XRD) and laser Raman spectroscopy, and device characteristics were evaluated by measuring hole mobility. Further, a heat treatment was performed as a post-treatment, and a change in the crystal structure was examined. XRD All membrane samples according to the embodiment of the present invention have 111 faces (2
(θ = 28.2 °) and peaks from the 220 plane (2θ = 47.2 °) were detected, confirming the crystallinity of silicon (cubic). On the other hand, it was confirmed that the film sample according to the comparative example had an amorphous structure. Laser Raman Spectroscopy All film samples according to the examples of the present invention have peaks due to crystallized silicon (Raman shift = 515-520c).
m- ¹ ) was detected, and crystal grains of 100 to 2000 mm were recognized. On the other hand, in the film sample according to the comparative example, a peak (Raman shift = 480 cm ⁻¹ ) due to the amorphous structure was detected.

Further, with respect to all the film samples according to the embodiments of the present invention, the crystal grain size and the crystal component ratio (the ratio of the crystal component peak intensity to the amorphous component peak intensity obtained by laser Raman spectroscopy) Represents.)
Are plotted against the thickness of the interface layer, and are shown in FIGS. 3A and 3B, respectively. According to this, the relationship between the thickness of the interface layer and the crystal grain size and the relationship between the thickness of the interface layer and the crystal component ratio show almost the same tendency. Thickness of 1000
It can be seen that within the range up to Å, the crystallinity is higher and the crystal grain size is larger than that of a film sample without such an interface layer (interface layer thickness = 0 °). For reference, a film sample according to a comparative example is similarly shown in the drawing. Heat treatment Each of the film samples obtained in the examples of the present invention and the comparative example was subjected to a heat treatment in vacuum at 500 ° C. for 8 hours as a post-treatment. However, in the example, the crystal grain size increased from 100 ° to 2000 ° to 500 ° to 3000 °. · Hole mobility The film sample according to the comparative example exhibited a hole mobility of 0.1 cm ² / V · s, whereas the film sample according to the example had a crystal grain size of 100 ° and 0.5 cm ² / V · s. And a hole diameter of 50 cm ² / V · s with a crystal grain size of 2000 °.

From the above results, it can be seen that a crystalline silicon film, which could not be obtained by the comparative example using the parallel plate type plasma CVD apparatus in the example of the present invention, was obtained at a low temperature of 300 ° C.

[0030]

According to the present invention, a high-quality crystalline silicon film formed at a relatively low temperature with a high productivity and a high-quality crystalline silicon film formed at a relatively low temperature with a high productivity can be formed. A method can be provided. More specifically, according to the present invention, the following effects can be obtained. The crystalline silicon film is composed of an interface layer and an upper film with the article to be formed, and crystallization seeds are formed in the interface layer by performing ion beam irradiation only during the formation of the interface layer. In addition, high quality crystal growth can be promoted by the crystal seeds in a state where impurities are not mixed and the film is not damaged by ion beam irradiation. Since the operation time of the ion source is short, the operating cost of the ion source can be reduced, the number of maintenance operations of the ion source can be reduced, and the operation time of the ion source can be reduced because the operation time of the ion source is short. The influence on other control systems of the apparatus can be reduced, and the stability of the entire film forming apparatus can be improved. The degree of vacuum in the vicinity of the surface of the article is 1 × 10 ⁻³ Torr
Since plasma is formed at a high vacuum of about 1 × 10 ⁻⁸ Torr, a diffusion region of radicals contributing to film formation is widened, and a crystalline silicon film can be easily formed on a large-area article to be formed. . In addition, the generation of unnecessary dust particles is reduced by suppressing the gas phase reaction, and a silicon film having good crystallinity can be more efficiently formed.
The burden of maintenance such as cleaning of the inside of the container where the film is formed is reduced. Because a crystalline silicon film can be obtained at a relatively low temperature,
For example, a film can be formed on a film-formed article made of a material having low heat resistance, such as low-melting glass, and the selection range of the film-formed article is widened. Since a high quality crystalline silicon film can be obtained in one process,
Heat treatment after film formation can be omitted, and productivity is good. Even when it is necessary to further increase the crystallinity, the temperature of the heat treatment performed as a post-treatment can be lowered, and the heating time can be shortened.

[Brief description of the drawings]

FIG. 1 is a view showing a schematic configuration of an example of an apparatus for forming a crystalline silicon film which can be used for carrying out the method of the present invention.

FIG. 2 is an enlarged sectional view of a part of one example of a crystalline silicon film according to the present invention.

FIG. 3 is a diagram showing a relationship (A) between the thickness of the interface layer and the crystal grain size and a relationship (B) between the thickness of the interface layer and the crystal component ratio in the crystalline silicon film according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Film-forming chamber 2 High-frequency electrode 21 Matching device 22 High-frequency power supply 3 Article holder / ground electrode 31 Heater 4 Ion source 5 Vacuum exhaust part 6 Plasma source gas supply part S Article to be film-formed

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI H01L 21/324 H01L 21/324 Z (56) References JP-A 1-245849 (JP, A) JP-A 2-271995 ( JP, A) JP-A-2-185019 (JP, A) JP-A-5-90158 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/205 C23C 14/14 C23C 14/22 C30B 29/06 504 H01L 21/20 H01L 21/324

Claims (12)

(57) [Claims] 1. A crystalline silicon film formed on an article to be formed under a plasma of a source gas containing a silicon-based gas by supplying plasma excitation energy, wherein the film is formed of An interface layer with the film article and an upper layer film, and the interface layer reduces the degree of vacuum in the vicinity of the article surface to 1 × 10 ^−3.
A layer in which the surface of the article is exposed to the plasma while maintaining the pressure at Torr to 1 × 10 ⁻⁸ Torr, and the surface of the article is irradiated with an ion beam to form silicon crystal seeds. Degree of vacuum near 1 × 10 ^-3
A crystalline silicon film, characterized in that the surface of the article is exposed to the plasma while maintaining the pressure at Torr to 1 × 10 ⁻⁸ Torr, and a silicon crystal is grown without irradiating an ion beam. 2. The crystalline silicon film according to claim 1, wherein the ion species of the ion beam is formed by using ions of at least one of an inert gas, a reactive gas, and a silicon-based gas. 3. An ion beam having an ion energy of 10
3. The crystalline silicon film according to claim 2, wherein the crystalline silicon film is formed by irradiation at 0 eV to 1 keV. 4. The method according to claim 1, wherein the source gas is formed using at least one kind of silicon-based gas, or at least one kind of silicon-based gas and at least one kind of reactive gas. 3. The crystalline silicon film according to any one of 3. 5. The method according to claim 1, wherein the temperature of the article is from room temperature to 600 °.
The crystalline silicon film according to claim 1, wherein the crystalline silicon film is formed as C. 6. The crystalline silicon film according to claim 1, wherein the crystalline silicon film is subjected to a heat treatment at 300 ° C. to 600 ° C. as a post-treatment after the film is formed. 7. A method for forming a crystalline silicon film on an article by exposing an article to be deposited to plasma by supplying a source gas containing a silicon-based gas by supplying energy for plasma excitation, and exposing the article to the plasma. Degree of vacuum near the surface of the article is 1 ×
After exposing the article surface to the plasma and irradiating the article surface with an ion beam while forming the interface layer containing the silicon crystal seeds on the article while maintaining the same at 10 ⁻³ Torr to 1 × 10 ⁻⁸ Torr, The ion beam irradiation is stopped, and the degree of vacuum near the surface of the article is continuously reduced to 1 × 10 ⁻³ Torr to 1 ×.
A method for forming a crystalline silicon film, comprising exposing the surface of the article to the plasma while maintaining the temperature at 10 ^-8 Torr to form an upper layer film of crystalline silicon. 8. The method for forming a crystalline silicon film according to claim 7, wherein ions of at least one of an inert gas, a reactive gas, and a silicon-based gas are used as ion species of the ion beam. 9. An ion beam having an ion energy of 10
9. The method for forming a crystalline silicon film according to claim 8, wherein the irradiation is performed at 0 eV to 1 keV. 10. The gas according to claim 7, wherein at least one of silicon-based gases or at least one of silicon-based gases and at least one of reactive gases is used as the source gas. Or a method for forming a crystalline silicon film. 11. The temperature of the article to be coated is from room temperature to 600.
The method for forming a crystalline silicon film according to any one of claims 7 to 10, wherein the temperature is set to ° C. 12. The method for forming a crystalline silicon film according to claim 7, wherein a heat treatment at 300 ° C. to 600 ° C. is performed on the crystalline silicon film as a post-processing after the film formation.