JPH0750268A - Amorphous silicon film and manufacturing method thereof - Google Patents

Abstract

(57) [Summary] [Constitution] The present invention is an amorphous silicon film formed on a substrate having a melting point of 290 ° C. or less, and has a bright conductivity of 5 × 10 ⁻⁶ S / cm or more. Amorphous silicon film and 30MHz or more 300MHz
The present invention relates to a method for producing an amorphous silicon film, which comprises forming an amorphous silicon film on a substrate by plasma-decomposing a gas containing a hydrogenated silicon gas using ultra-high frequency waves having the following frequencies. According to the present invention, even on a material having a low melting point,
Since a high-quality amorphous silicon film can be formed, an inexpensive plastic material having low heat resistance can be used as a substrate, and an inexpensive solar cell, active matrix display, image sensor or the like can be provided.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention is formed on a substrate,
For solar cells, thin film transistors, image sensors, etc.
The present invention relates to an intrinsic semiconductor amorphous silicon film used by being laminated with a p-type semiconductor layer, an n-type semiconductor layer, or the like, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Amorphous silicon films are used in solar cells, image sensors and liquid crystal displays in the form of diodes and thin film transistors. In order to realize characteristics suitable for these applications, amorphous silicon films are usually used. The film is formed on a glass or metal substrate heated to 250 to 300 ° C. As a method for producing an amorphous silicon film, for example, “Journal of Applied Physics Vol. 23 (1984) by Junji Shirafuji et al.
The method described in 1278 "is known. That is, this method uses a high frequency of 13.56 MHz and SiH ₄
The gas is plasma decomposed to form an amorphous silicon film on a glass substrate heated to 70 ° C to 270 ° C. However, in this method, in order to obtain an amorphous silicon film having high bright conductivity, the substrate temperature must be increased to 200 ° C. or higher,
When a film is formed at a substrate temperature of 170 ° C. or less, 1 × 10 ⁻⁶ S
Only a film having a low bright conductivity of / cm can be obtained.

On the other hand, in these applications, there are demands for weight reduction of products, improvement of productivity, flexibility for curved surface processing, cost reduction, and the like. If plastic, especially a general-purpose plastic film such as a polyester film, can be adopted as the substrate, it is possible to meet the above requirements together with the introduction of roll-to-roll type production equipment using a long substrate. However, general-purpose plastics are 250-30
It does not have heat resistance (operating temperature range) as high as 0 ° C., and it is desired to lower the temperature when forming an amorphous silicon film.

Since a material having a low melting point or a plastic material can be molded into an arbitrary shape at a low temperature,
Since the processing cost is low, and the plastic material has advantages that it can be light in weight and is hard to break, it is desired to form a high quality amorphous silicon film on these materials. When using plastics, especially plastic films as the substrate,
In addition to the limitation of heat resistance, it is an important issue to reduce the amorphous silicon film forming temperature in order to reduce the warpage due to the difference in thermal expansion coefficient. This is because if the warpage is large, it becomes difficult to carry out fine processing such as photolithography and laser scribing and handling when processing into a solar cell or a thin film transistor element. Also, when a plastic is heated, a low molecular weight substance called an oligomer is released, but the oligomer may open a pinhole in the film formed on the plastic, deteriorate the film quality, or reduce the adhesive force between the film and the substrate. To do. The higher the heating temperature is, the larger the amount of released oligomers becomes. Therefore, reducing the amorphous silicon film forming temperature is an effective measure.

When the temperature of the amorphous silicon film is lowered, a substrate such as glass or metal having high heat resistance is used in order to reduce warpage and peeling of the film due to a difference in thermal expansion coefficient between the substrate and the amorphous silicon film. It is also effective when used.

In a solar cell, a transparent conductive film is used to guide light into the device, and a transparent conductive film, a diode and a back electrode are laminated in this order on a substrate. As the transparent conductive film, an oxide film such as ITO (tin oxide-doped indium oxide), tin oxide, or zinc oxide, which can be made thin and has a low resistance, is used.

However, when the silicon film or the silicon compound film is laminated on the transparent oxide conductive film by plasma decomposition, oxygen atoms are extracted by excited hydrogen atoms in the plasma and damaged. There are problems that the resistance value increases, the surface becomes rough, and the transmittance decreases. Further, there is a problem that diffusion of metal atoms into the semiconductor film caused by abstraction of oxygen atoms and deterioration of characteristics of the semiconductor film due to diffusion. Excited hydrogen atoms in plasma have a strong penetrating power, and dozens of nanometers stacked on the transparent conductive film.
The transparent conductive film is damaged through the silicon-based film having a thickness of m. Damage caused by excited hydrogen atoms in plasma is remarkable in ITO in the transparent oxide conductive film, followed by tin oxide, and zinc oxide is said to have the best plasma resistance. Since the resistance value can be lowered in the order of ITO, tin oxide, and zinc oxide, there is a trade-off relationship between low resistance and plasma resistance. Attempts have been made to stack ITO, tin oxide, and zinc oxide on a substrate in this order to achieve both low resistance and plasma resistance, but zinc oxide with the highest plasma resistance is also exposed to hydrogen plasma. It causes a decrease in transmittance.
In addition, a zinc oxide film having high plasma resistance can reduce the temperature of the substrate to 3
Although it can be obtained at a high temperature of 00 ° C., such a high substrate temperature is difficult to adopt when a substrate having relatively low heat resistance such as plastic is used as the substrate.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide an amorphous silicon film having a high bright conductivity while being formed on a substrate having a low melting point, and a method for manufacturing the same.

[0009]

The object of the present invention is achieved by the following constitution and manufacturing method.

That is, an amorphous silicon film formed on a substrate having a melting point of 290 ° C. or lower, characterized by a bright conductivity of 5 × 10 ⁻⁶ S / cm or more, and 30 MHz. More than 300MH
A method for producing an amorphous silicon film, which comprises forming an amorphous silicon film on a substrate by plasma-decomposing a gas containing a silicon hydride gas by using an ultrashort wave having a frequency of z or less.

It is important that the amorphous silicon film according to the present invention has a bright conductivity of 5 × 10 ⁻⁶ S / cm or more. Bright conductivity refers to the conductivity when light of AM-1 100 mW / cm ² by a solar simulator is vertically incident on the film, and is the conductivity when the film is not exposed to light at all. Contrast with dark conductivity. If this bright conductivity is less than 5 × 10 ⁻⁶ S / cm, the conversion efficiency when used in a solar cell may be low,
When it is used for a thin film transistor, it does not operate at high speed, so a practical one cannot be obtained. More preferably, 5
× 10 ⁻⁵ S / cm or more. The light conductivity and the dark conductivity are measured, for example, by a method called a direct current two-terminal method.

The amorphous silicon film preferably has a light-dark conductivity ratio (bright conductivity / dark conductivity) of 1 × 10 ⁵ or more. If the light-dark conductivity ratio is less than 1 × 10 ⁵ , even if the light conductivity is high, the conversion efficiency will be low when used in a solar cell, and the leakage current will be large when used in a thin film transistor, resulting in malfunction. Is likely to occur, which is not preferable. Bright / dark conductivity ratio is 1 × 10
It is more preferably ⁶ or more.

SiH in the amorphous silicon film
The ratio of ₂ bond to SiH bond is preferably 0.05 or less. Furthermore, it is preferable that SiH ₂ bonds exist only at the measurement limit. When this ratio is larger than 0.05, when used in a solar cell, the conversion efficiency is likely to drop significantly due to photodegradation, which is not preferable. This ratio is measured, for example, by measuring a reflection spectrum or an absorption spectrum by infrared spectroscopy and obtaining the area ratio thereof.

Next, a method for manufacturing an amorphous silicon film according to the present invention will be described. That is, 30 MH
It is a method of forming an amorphous silicon film on a substrate by plasma-decomposing a gas containing a hydrogenated silicon gas by using an ultrashort wave having a frequency of z or more and 300 MHz or less.

Here, it is important that the frequency of the power source used for plasma decomposition is 30 MHz or more and 300 MHz or less. When a film is formed using an ultra short wave with a frequency of less than 30 MHz as a power source, the electron density of plasma does not increase so much, the deposition rate decreases, and the self-bias of the substrate increases, so that the film is damaged by plasma damage. There is a case where the bright conductivity of is decreased. When an ultra short wave with a frequency over 300 MHz is used as a power source, it is difficult to match the electrodes with the power source, it is difficult to form a film having a uniform thickness on a large area, and plasma is efficiently maintained. Can be difficult. Furthermore, it is more preferable to use ultrashort waves having a frequency of 50 MHz or more and 200 MHz or less.

The temperature of the substrate is maintained at 170 ° C. by using the ultrashort wave having a frequency of 30 MHz or more and 300 MHz or less.
Even if kept below, a high-quality amorphous silicon film having high bright conductivity can be formed on the substrate. Therefore, a high quality amorphous silicon film can be formed even on a substrate made of a material such as a plastic material having a low melting point and low heat resistance. Specifically, a film having a high bright conductivity can be easily formed on a substrate having a melting point of 290 ° C. or lower, and further on a substrate having a melting point of 240 ° C. or lower.

Of course, in the manufacturing method according to the present invention, not only on a substrate having a melting point of 290 ° C. or less, but also a melting point of 290 ° C.
It is also preferably applied to the case of forming an amorphous silicon film on a substrate that exceeds the above. Even in such a substrate, by lowering the temperature of the substrate, it is possible to prevent deformation due to strain of the substrate, deformation due to a difference in coefficient of thermal expansion from the amorphous silicon film, or peeling of the amorphous silicon film from the substrate.

As the substrate, a plastic material, a metal material, a ceramic material, silicate glass, quartz, silicon or the like can be used. Among these, as the flexible substrate, a plastic material, a metal material, a part of a ceramic material, or the like can be used.

As the silicate glass, barium borosilicate glass or aluminum borosilicate glass containing no sodium can be adopted. In the case of silicate glass containing sodium, it is preferable that the surface thereof is coated with a barrier layer such as a silicon oxide film for preventing elution of sodium.

As the flexible substrate, a plastic material, a metal material, a part of a ceramic material, or the like can be used as described above. Specifically, it is molded into a thin plate or film. Examples include plastic materials, metal materials, and some ceramic materials. Since the flexible substrate can be wound in a roll shape, when a film is formed on the flexible substrate, it can be manufactured using a film forming apparatus equipped with a long substrate traveling system, and productivity can be improved. There are advantages. In addition, it has advantages that it can be easily transported and that it can be processed into a product having a curved surface. further,
When a plastic material is used as the flexible substrate, the weight per area of the substrate can be made lighter than that of the ceramic material or the metal material, so that the weight of the amorphous silicon product can be reduced and the film forming apparatus can be simplified. There are advantages that can be realized.

Examples of the plastic material include polyesters such as polyethylene terephthalate, polyethylene naphthalate and polycarbonate, polyolefins such as polypropylene, polyarylene sulfides such as polyphenylene sulfide, polyamides, aromatic polyamides and polyether ketones. And polyimides can be used. Of these, the melting point is 290
As for those below ℃, polyethylene terephthalate,
Acetate, polyphenylene sulfide, and the like are preferably used, and those having a melting point of 240 ° C. or lower include polycarbonate, polystyrene, nylon, polypropylene, polyvinyl chloride, and the like, and are preferably used. When these are used in the form of a film, they are preferably biaxially stretched from the viewpoint of mechanical stability and strength. The heat resistance of a plastic material varies depending on the molding method, additives, usage method and the like and cannot be determined in a general manner, but an index called a usage temperature range in which mechanical properties are generally maintained can be used as a standard.

When the substrate is transparent for solar cell applications, a transparent conductive film is first formed on the substrate, and a p-type or n-type doped silicon-based semiconductor film is formed on the transparent conductive film.
Next, a non-doped amorphous silicon film and a doped silicon semiconductor film of a type opposite to the silicon semiconductor film directly above the transparent conductive film are laminated in this order to form a pin diode. As a silicon-based semiconductor film,
In addition to Si such as amorphous silicon, SiC, Si
Ge, SiAl, SiGa, SiS, SiSn and the like can be cited, but an amorphous silicon film, a microcrystalline silicon film, or a SiC film is preferably adopted for a solar cell having a non-doped amorphous silicon film. As the transparent conductive film, oxides such as ITO, tin oxide, fluorine-doped tin oxide, zinc oxide, and zinc oxide-aluminum oxide, which have high transparency and can reduce resistance, are preferably adopted. The doping amount of tin oxide in ITO is preferably 2 to 20%. These oxide transparent conductive films do not have good resistance to excited hydrogen atoms, and when a gas containing a hydrogenated silicon gas is plasma-decomposed to form an amorphous silicon film, the resistance value increases, the transparency decreases, and the surface is reduced. Often causes rough spots. In particular, ITO and tin oxide have poor resistance, and the higher the temperature, the more the resistance increases, the transparency decreases, and the surface becomes more rough. The thickness of the doped silicon-based semiconductor film laminated on the transparent conductive film of the solar cell element is usually 0.5 nm to 70 nm.
Excited hydrogen atoms in the plasma have strong penetrating power and damage the transparent conductive film through the silicon-based semiconductor film having a thickness of 0.5 nm to 70 nm stacked on the transparent conductive film. The surface roughness may serve as a core of deposition when an amorphous silicon film is stacked on the surface, which may cause formation of coarse particles and white turbidity, or may cause pinholes. According to the present invention, a high-quality amorphous silicon film can be formed at a low substrate temperature, and an increase in the resistance value of an oxide transparent conductive film and a decrease in transparency can be suppressed. In the plasma decomposition by the ultra-short wave of the present invention, the potential of the plasma is small, so that the damage to the transparent conductive film from the plasma can be further reduced, and the effect of suppressing the characteristic deterioration of the transparent conductive film is great.

As the film forming apparatus, for example, a parallel plate capacitive coupling type plasma CVD apparatus can be used. The power of the ultra-short wave used for decomposition is preferably in the range of 80 mW / cm ² or more and 1 W / cm ² or less as the power of the ultra-short wave divided by the cathode area. When the decomposition is performed with an energy larger than 1 W / cm ^{2, the} film may have a low light conductivity or a high dark conductivity due to plasma damage. Ultra-short wave power is 0.5 W / c
It is more preferably m ² or less. Ultra shortwave power is 8
It is preferable that it is 0 mW / cm ² or more because it is effective because the ratio of SiH ₂ bond to SiH bond in the amorphous silicon film is 0.05 or less. 80 shortwave power
When the mW / cm ² or more is set, the substrate temperature is 170 ° C.
Below, when the amorphous silicon film is formed under the constraint that the frequency of the ultra-high frequency is 100 MHz or less and the value of the flow rate of hydrogen gas / the flow rate of silicon hydride gas is 3.5 or less.
The effect is particularly large because the ratio of H ₂ bond to SiH bond is set to 0.05 or less. Increasing the ratio of the hydrogen gas flow rate / silicon hydride gas flow rate is preferable in order to reduce the ratio of SiH ₂ bonds and SiH bonds in the amorphous silicon film. There is a problem that gets worse. Further, the upper limit of the frequency of the ultra-high frequency that can be applied to the electrode may be limited to 100 MHz or less depending on the electrode structure of the plasma CVD apparatus (capacitance between the earth and the electrode and wiring, electrode area, etc.).

The distance between the electrode substrates is preferably 8 mm or more and 80 mm or less. When it is less than 8 mm, the bright conductivity or dark conductivity of the film may be decreased due to plasma damage, and when it is longer than 80 mm, discharge may be difficult or the deposition rate may be decreased. , May be disadvantageous in practical use. The pressure inside the apparatus during film formation is preferably maintained at 0.01 Torr or more and 5 Torr or less. If it is less than 0.01 Torr, discharge may be difficult or the deposition rate may be low, which may be disadvantageous in practical use. When it is higher than 5 Torr, the light conductivity of the film may be decreased or the dark conductivity thereof may be increased.

As the gas containing the silicon hydride gas used for the decomposition, SiH ₄ , Si ₂ H ₆ , Si ₃ H ₈ ,
It is possible to use hydrogenated silicon gas such as SiHF ₃ , SiH ₂ F ₂ and SiH ₂ Cl ₂ alone or to use a mixed gas of these hydrogenated silicon gas and other gas such as hydrogen, helium and argon. it can.

The flow rate of silicon hydride gas in terms of standard state volume is a, the flow rate of hydrogen gas in terms of standard state volume is b, the flow rate of helium gas in terms of standard state volume is c, and the flow rate of argon gas is Flow rate in standard state volume conversion d
Then, the gas mixture ratios are a / b ≧ 0.0, respectively.
1, a / c ≧ 0.01, and a / d ≧ 0.01 are preferable. a / b <0.01, a / c <0.01 or a
When /d<0.01, the film may be crystallized or the deposition rate may be reduced, which may be disadvantageous in practical use.

The amorphous silicon film according to the present invention and the amorphous silicon film produced according to the present invention are intrinsic semiconductor amorphous silicon films, are formed on a substrate, and are laminated with a p-type semiconductor layer or an n-type semiconductor layer. Are used for solar cells, thin film transistors, image sensors, etc.

[0028]

【Example】

[Characteristic Measurement / Evaluation Method] (1) Conductivity Measurement The conductivity is measured by providing a coplanar type electrode by gold deposition, applying a voltage at two terminals, and measuring the current to determine the conductivity. It was calculated. At the time of measuring the light conductivity, a solar simulator was used to irradiate AM-1 light with an intensity of 100 mW / cm ² at room temperature.

(2) SiH in the amorphous silicon film
Measurement of abundance ratio of SiH ₂ bonds and SiH bond of the measurement amorphous silicon film of ₂ bonds and abundance ratio of SiH bonds by infrared spectroscopy, and 2000 cm ^-1 from the reflection spectrum or absorption spectrum 2080
From the area ratio of the peak with its center at cm ^-1 , 2000
The peak with the discontinued cm ^-1 and by SiH bond, SiH peaks with that discontinued 2080Cm ^-1
Calculated as due to ₂ bonds. Bruker's IFS-120HR was used for the apparatus.

(3) Measurement of energy conversion efficiency While irradiating the manufactured solar cell with AM-1 light at an intensity of 100 mW / cm ² , the p-type layer side of the diode constituting the solar cell was made positive by a bipolar power source. The voltage is applied as described above. The voltage is increased from 0, and the voltage-current characteristic up to the point where the current becomes 0 is measured. The energy conversion efficiency is obtained by dividing the maximum value of the product of voltage and current on the voltage-current characteristics by the area of the solar cell and the light intensity of 100 mW / cm ² .

Example 1 As the film forming apparatus, a capacitively coupled plasma CVD apparatus having an electrode area of 400 cm ^{2 and a} parallel plate was used. The distance between electrode substrates is 30 mm, and the pressure during discharge is 0.3 Torr
And the gas flow rate is SiH ₄ 25 sccm, H ₂ 125 s
It was set to ccm. The frequency of the ultrashort wave was set to 130 MHz, and plasma was generated with an electric power of 15 W. Barium borosilicate glass (melting point 1160 ° C.) is used for the substrate, and the substrate temperature is 170
Film formation was performed at ° C. A film having a thickness of 600 nm was formed in 10 minutes. The light conductivity and the dark conductivity of this film were measured and found to be 6 × 10 ⁻⁵ S / cm and 3 × 10 ⁻¹¹ S, respectively.
/ Cm, and the light / dark conductivity ratio was 2.0 × 10 ⁶ . The ratio of the number of SiH ₂ bonds to the number of SiH bonds in the film is
It was less than 0.01.

Example 2 As the film forming apparatus, a capacitively coupled plasma CVD apparatus having an electrode area of 400 cm ^{2 and a} parallel plate was used. The distance between electrode substrates is 28 mm, and the pressure during discharge is 0.5 Torr
And the gas flow rate is SiH ₄ 25 sccm, H ₂ 100 s
It was set to ccm. Plasma was generated at an electric power of 20 W with the frequency of the ultra-short wave set to 80 MHz. Barium borosilicate glass (melting point 1160 ° C) is used for the substrate, and the substrate temperature is 150 ° C.
Then, a film was formed. A film having a film thickness of 550 nm was formed in 10 minutes. When the light conductivity and the dark conductivity of this film were measured, they were 7 × 10 ⁻⁵ S / cm and 4 × 10 ⁻¹¹ S / cm, respectively.
cm, and the light / dark conductivity ratio was 1.8 × 10 ⁶ .
The ratio of the number of SiH ₂ bonds to the number of SiH bonds in the film is 0.
It was less than 01.

Example 3 As the film forming apparatus, a capacitively coupled plasma CVD apparatus having an electrode area of 400 cm ^{2 and a} parallel plate was used. The distance between electrode substrates is 30 mm, and the pressure during discharge is 0.8 Torr
And the gas flow rate is SiH ₄ 25 sccm, H ₂ 100 s
It was set to ccm. Plasma was generated at an electric power of 10 W with the frequency of the ultra-short wave set to 100 MHz. Quartz glass (melting point: 1730 ° C.) was used as a substrate, and a film was formed at a substrate temperature of 120 ° C. A film having a film thickness of 500 nm was formed in 10 minutes. When the light conductivity and the dark conductivity of this film were measured, they were 8 × 10 ⁻⁵ S / cm and 6 × 10 ⁻¹¹ S / cm, respectively, and the light / dark conductivity ratio was 1.3 × 10 ⁶ . . S in the film
The ratio of the number of iH ₂ bonds to the number of SiH bonds was 0.01.

Example 4 The same as Example 1 except that the substrate temperature was 150 ° C., using a 25 μm thick polyimide film (without melting point) that was heat-treated at 200 ° C. for 1 hour in vacuum. A film was formed. A film having a film thickness of 612 nm was formed in 12 minutes. When the light conductivity and the dark conductivity of this film were measured, they were 8 × 10 ⁻⁵ S / cm and 5 × 10 ⁻¹¹ S / c, respectively.
m, and the light / dark conductivity ratio was 1.6 × 10 ⁶ . The ratio of the number of SiH ₂ bonds to the number of SiH bonds in the film is 0.0
It was less than 1.

Example 5 The same as Example 2 except that a polyethylene terephthalate film having a thickness of 25 μm (melting point 263 ° C.) which was heat-treated at 140 ° C. for 1 hour in vacuum was used as the substrate and the substrate temperature was 120 ° C. A film was formed in the same manner. A film having a film thickness of 612 nm was formed in 12 minutes. When the light conductivity and the dark conductivity of this film were measured, each was 5 × 10 ⁻⁵ S / cm,
4 × 10 ⁻¹¹ S / cm, and the light / dark conductivity ratio is 1.3 ×
It was 10 ⁶ . The ratio of the number of SiH ₂ bonds to the number of SiH bonds in the film was 0.01. Example 6 A 25 μm-thick polypropylene film (melting point: 160) was obtained by subjecting a substrate to a heat treatment in vacuum at 130 ° C. for 1 hour.
˜170 ° C.) and the substrate temperature was 100 ° C.
A film was formed in the same manner as in Example 3. Film thickness 5 in 10 minutes
A 03 nm film was formed. When the light conductivity and the dark conductivity of this film were measured, they were 8 × 10 ⁻⁵ S / cm and 6 ×, respectively.
10 ^-11 S / cm, and light-dark conductivity ratio is 1.3 × 10
^{Was 6} . The ratio of the number of SiH ₂ bonds to the number of SiH bonds in the film was 0.02.

Example 7 The same as Example 1 except that a 25 μm-thick polyphenylene sulfide film (melting point 285 ° C.) heat-treated in vacuum at 180 ° C. for 1 hour was used as the substrate and the substrate temperature was 140 ° C. A film was formed in the same manner. A film having a film thickness of 503 nm was formed in 10 minutes. When the light conductivity and the dark conductivity of this film were measured, each was 1 × 10 ⁻⁴ S / cm,
6 × 10 ^-11 S / cm, and the light-dark conductivity ratio is 1.7 ×
It was 10 ⁶ . The ratio of the number of SiH ₂ bonds to the number of SiH bonds in the film was 0.02. Example 8 As the film forming apparatus, a capacitively coupled plasma CVD apparatus having an electrode area of 400 cm ² parallel plates was used. The distance between electrode substrates is 35 mm, and the pressure during discharge is 0.6 Torr
And the gas flow rate is SiH ₄ 25 sccm, H ₂ 150 s
It was set to ccm. Plasma was generated at a power of 5 W with the frequency of the ultra-short wave set to 160 MHz. Substrate 14 in vacuum
A film was formed at a substrate temperature of 120 ° C. using a 25 μm-thick polycarbonate film (melting point 222 to 230 ° C.) that was heat-treated at 0 ° C. for 1 hour. Time 15
A film having a thickness of 420 nm was formed in a minute. When the light conductivity and the dark conductivity of this film were measured, each was 6 × 10 ⁻⁶ S /
cm, 4 × 10 ⁻¹¹ S / cm, and the light / dark conductivity ratio was 1.5 × 10 ⁵ . Number of SiH ₂ bonds and S in the film
The ratio of the number of iH bonds was less than 0.01.

Example 9 A film was formed in the same manner as in Example 8 except that the frequency of ultra-high frequency was 140 MHz and the power was 10 W. A film having a film thickness of 513 nm was formed in 15 minutes. When the light conductivity and the dark conductivity of this film were measured, each was 9 × 10
^{It was −5} S / cm, 6 × 10 ⁻¹¹ S / cm, and the light / dark conductivity ratio was 1.5 × 10 ⁶ . The ratio of the number of SiH ₂ bonds to the number of SiH bonds in the film was less than 0.01.

Example 10 The same film forming apparatus as in Example 1 was used, the distance between electrode substrates was 35 mm, and the pressure during discharge was 0.6 T.
orr and the gas flow rate is SiH ₄ 25sccm, H ₂ 1
It was set to 25 sccm. Plasma was generated at an electric power of 14 W with an ultra-short wave frequency of 75 MHz. The substrate was heat-treated in vacuum at 180 ° C for 1 hour and had a thickness of 25μ.
m polyphenylene sulfide film (melting point 285
C.) was used at a substrate temperature of 140.degree.
A film having a film thickness of 520 nm was formed in 12 minutes. When the light conductivity and the dark conductivity of this film were measured, each was 1 × 1.
It was 0 ⁻⁴ S / cm, 8 × 10 ⁻¹¹ S / cm, and the light / dark conductivity ratio was 1.3 × 10 ⁶ . The ratio of the number of SiH ₂ bonds to the number of SiH bonds in the film was 0.01.

Example 11 The same film forming apparatus as in Example 1 was used, the distance between the electrode substrates was 35 mm, and the pressure during discharge was 0.6 T.
orr and the gas flow rate is Si ₂ H ₆ 15 sccm, H ₂
It was set to 80 sccm. Plasma was generated at a power of 18 W with an ultra-short wave frequency of 150 MHz. The substrate was heat-treated in vacuum at 160 ° C for 1 hour and had a thickness of 25μ.
m polycarbonate film (melting point 222-230
C.) was used at a substrate temperature of 140.degree.
A film having a film thickness of 650 nm was formed in 10 minutes. When the light conductivity and the dark conductivity of this film were measured, each was 4 × 1.
It was 0 ⁻⁵ S / cm, 3 × 10 ⁻¹¹ S / cm, and the light / dark conductivity ratio was 1.3 × 10 ⁶ . The ratio of the number of SiH ₂ bonds to the number of SiH bonds in the film was 0.02.

Example 12 The same film forming apparatus as in Example 1 was used, the distance between electrode substrates was 35 mm, and the pressure during discharge was 0.1 T.
orr and the gas flow rate is Si ₂ H ₆ 12sccm, H ₂
It was set to 40 sccm. Plasma was generated at a power of 18 W with an ultra-short wave frequency of 200 MHz. The substrate was heat-treated in vacuum at 180 ° C for 1 hour and had a thickness of 25μ.
m polyphenylene sulfide film (melting point 285
C.) was used at a substrate temperature of 140.degree.
A film having a film thickness of 520 nm was formed in 8 minutes. When the light conductivity and the dark conductivity of this film were measured, each was 5 × 10 5.
^{It was −5} S / cm, 3 × 10 ⁻¹¹ S / cm, and the light / dark conductivity ratio was 1.7 × 10 ⁶ . The ratio of the number of SiH ₂ bonds to the number of SiH bonds in the film was 0.02.

Example 13 The same film forming apparatus as in Example 1 was used, the distance between the electrode substrates was 35 mm, and the pressure during discharge was 0.1 T.
orr and the gas flow rate is Si ₂ H _{6 10} sccm, H ₂
It was set to 30 sccm. Plasma was generated at an electric power of 16 W with an ultra-short wave frequency of 250 MHz. The substrate was heat-treated in vacuum at 180 ° C for 1 hour and had a thickness of 25μ.
m polyphenylene sulfide film (melting point 285
C.) was used at a substrate temperature of 140.degree.
A film having a film thickness of 460 nm was formed in 8 minutes. The light conductivity and the dark conductivity of this film were measured and found to be 3 × 10
^{It was −5} S / cm, 2 × 10 ⁻¹¹ S / cm, and the light / dark conductivity ratio was 1.5 × 10 ⁶ . The ratio of the number of SiH ₂ bonds to the number of SiH bonds in the film was 0.03.

Example 14 The same film forming apparatus as in Example 1 was used, the distance between the electrode substrates was 50 mm, and the pressure during discharge was 0.3 T.
orr and the gas flow rate was SiH ₄ 25 sccm.
Plasma was generated at an electric power of 40 W with an ultrashort frequency of 90 MHz. Quartz substrate (melting point 1730 ° C)
Was used to form a film at a substrate temperature of 200 ° C. Time 1
A film having a thickness of 580 nm was formed in 0 minutes. The light conductivity and the dark conductivity of this film were measured and found to be 7 × 10 ⁻⁴ S
/ Cm, 1 × 10 ⁻¹¹ S / cm, and the light / dark conductivity ratio was 7.0 × 10 ⁷ . Number of SiH ₂ bonds and S in the film
The ratio of the number of iH bonds was less than 0.01.

Example 15 The same film forming apparatus as in Example 1 was used, the distance between the electrode substrates was 30 mm, and the pressure during discharge was 0.4 T.
orr and the gas flow rate is SiH ₄ 52sccm, H ₂ 1
It was set to 66 sccm. The frequency of the ultra-short wave is 70 MHz, and the power is 22 W (55 mW / cm ² ), 40 W (10
0 mW / cm ² ), 60 W (150 mW / cm ² ), 8
Plasma was generated by changing it to 0 W (200 mW / cm ² ). Barium borosilicate glass (melting point 116
0 ° C.) and a substrate temperature of 150 ° C. to form a film having a thickness of 500 nm. The light conductivity and the dark conductivity of these films were measured and found to be as shown in Table 1. The relationship between the power of ultrashort waves and the ratio of the number of SiH ₂ bonds to the number of SiH bonds in these films is shown in FIG. S when the power is 55 mW / cm ^2.
The ratio of the number of iH ₂ bonds to the number of SiH bonds was as large as 1.07, but when the power was 100 mW / cm ² or more, SiH ₂
The ratio of the number of bonds to the number of SiH bonds was as good as 0.05 or less.

[0044]

[Table 1] Example 16 400 on barium borosilicate glass (melting point 1160 ° C.)
The substrate on which the ITO film of nm thickness was formed was used. Using the same plasma CVD apparatus as in Example 1, the distance between electrode substrates was 30 mm, the pressure during discharge was 0.4 Torr, the gas flow rate was SiH ₄ 25 sccm, H ₂ 80 sccm, B ₂ H ₆
0.5% -H ₂ 100sccm, the frequency of VHF 70
Plasma was generated at MHz and power of 40 W. A 15-nm-thick amorphous silicon film doped with boron was formed at a substrate temperature of 150 ° C. Then, the distance between the electrode substrates is set to 3 by using another chamber of the same device with the same specifications
0 mm, discharge pressure 0.5 Torr, gas flow rate S
Plasma is generated with iH ₄ 50 sccm, H ₂ 200 sccm, ultra-short wave frequency of 70 MHz, and ultra-short wave power of 40 W to generate a plasma on the amorphous silicon film doped with boron at a substrate temperature of 150 ° C. and a thickness of 5 ° C.
A non-doped amorphous silicon film having a thickness of 00 nm was formed. Next, using another chamber of the same device with the same specifications, the distance between the electrode substrates was 30 mm and the pressure during discharge was 0.4.
Torr, gas flow rate is SiH ₄ 25 sccm, H ₂ 80
sccm, PH ₃ 1% -H ₂ 100 sccm, the frequency of the ultra short wave was 70 MHz, and the electric power of the ultra short wave was 40 W to generate plasma, and the substrate temperature was 150 ° C. and the phosphorus of 30 nm thick was formed on the non-doped amorphous silicon film. A doped amorphous silicon film was formed. An aluminum film having a thickness of 200 nm and a size of 10 mm was formed on the phosphorus-doped amorphous silicon film by a vacuum deposition method. When the voltage-current characteristics were measured while irradiating the solar cell thus obtained with AM-1 light at an intensity of 100 mW / cm ² , the energy conversion efficiency was 6.2%, which was good.

Comparative Example 1 A solar cell was produced in the same manner as in Example 16 except that the plasma excitation frequency when forming a non-doped amorphous silicon film was 13.56 MHz. AM-1 light was applied to the solar cell thus obtained at 100 mW / cm
^{When the} voltage-current characteristics were measured while irradiating with the intensity of ² , the energy conversion efficiency was as small as 2%. It is presumed that the ITO film was damaged when the non-doped amorphous silicon film was formed, and the resistance value increased.

[0046]

According to the present invention, a high-quality amorphous silicon film having a high bright conductivity can be formed on a substrate having a melting point of 290 ° C. or lower. As a result, an inexpensive plastic material having low heat resistance can be used as the substrate, and an inexpensive solar cell, active matrix display, image sensor or the like can be provided.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the power of ultra-high frequency in Example 15, the number of SiH ₂ bonds in an amorphous silicon film, and the ratio of the number of SiH bonds.

Claims (15)

[Claims] 1. An amorphous silicon film formed on a substrate having a melting point of 290 ° C. or lower, and having a bright conductivity of 5 × 10 5.
^-6 S / cm or more, an amorphous silicon film. 2. The amorphous silicon film according to claim 1, wherein the melting point of the substrate is 240 ° C. or lower. 3. The amorphous silicon film according to claim 1, wherein the substrate is a flexible substrate. 4. The amorphous silicon film according to claim 1, wherein the substrate is plastic. 5. The amorphous silicon film according to any one of claims 1 to 4, wherein the light-dark conductivity ratio is 1 × 10 ⁵ or more. 6. The amorphous silicon film according to claim 1, wherein the ratio of SiH ₂ bond to SiH bond in the amorphous silicon film is 0.05 or less. 7. A method for producing an amorphous silicon film, characterized by forming an amorphous silicon film on a substrate by plasma-decomposing a gas containing a hydrogenated silicon gas by using an ultrashort wave in the range of 30 MHz or more and 300 MHz or less. Method. 8. The method for producing an amorphous silicon film according to claim 7, wherein the amorphous silicon film is formed on a substrate kept at 170 ° C. or lower. 9. The method for producing an amorphous silicon film according to claim 7, wherein the amorphous silicon film is formed on a substrate having a melting point of 290 ° C. or lower. 10. The method for producing an amorphous silicon film according to claim 7, wherein the amorphous silicon film is formed on a substrate having a melting point of 240 ° C. or lower. 11. A gas containing silicon hydride gas is a silicon hydride gas simple substance or a mixed gas of silicon hydride gas and at least one selected from the group consisting of hydrogen, helium and argon. The method for producing an amorphous silicon film according to claim 7. 12. The frequency of ultra-high frequency is 55 MHz or more 20
The method for producing an amorphous silicon film according to claim 7, wherein the range is 0 MHz or less. 13. The method for producing an amorphous silicon film according to claim 7, wherein the power value of the ultrashort wave divided by the area of the cathode electrode is 80 mW / cm ² or more and 1 W / cm ² or less. 14. A non-doped amorphous silicon film is formed on a substrate on which a transparent conductive film made of an oxide is formed with a doped silicon semiconductor film of 70 nm or less interposed therebetween. Method for manufacturing amorphous silicon film. 15. The method for producing a semiconductor film according to claim 14, wherein the transparent conductive film made of an oxide is tin oxide-doped indium oxide, tin oxide, zinc oxide, or a laminated body thereof.