JPH0424430B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention produces an amorphous silicon film (hereinafter referred to as an a-Si film) by thermally decomposing a high-order silane gas represented by the general formula SinH ₂ n ₊₂ (where n is an integer of n≧2) and depositing it on a substrate. More specifically, regarding the method of forming a with a wide band gap,
-Relating to a method of forming a Si film. Since the a-Si film has excellent photoelectric properties, it can be used in solar cells, photoreceptors, thin film transistors,
Used in optical sensors, etc. However, in order to utilize light more effectively, a film with a wider optical band gap Egopt (an optical evaluation of the band gap) is required. The optical bandgap (hereinafter simply referred to as bandgap) of a film is closely related to physical properties such as dark conductivity, photosensitivity, and heat resistance, and has a very important meaning in defining the properties of the film. For example, (i) pin-a-Si solar cells require a material with a wider bandgap in the window layer.
However, if the bandgap material has a narrow window layer, light absorption will increase in the surface layer where no electric field is applied, making it impossible to utilize it effectively, whereas if the bandgap of the window layer is wide, more light can be taken in. This is because high photoelectric conversion efficiency can be obtained. However, when targeting sunlight,
Most of its energy intensity is visible light (1.6~
3.1eV), it is therefore desirable that the bandgap of the window layer has a width of at least 1.6eV. (ii) In addition, in a-Si films used as electrophotographic photoreceptors and image pickup tube devices, the sensitivity to red light generally tends to be too high compared to the sensitivity to blue light, although it depends on the nature of the light. Therefore, increasing the band gap to increase the resistance has become an important issue, and for this purpose, it is desirable to increase the band gap to 1.8 eV or higher, for example. (iii) Furthermore, in heat-resistant transistors, since semiconductors operate at high temperatures, a wide bandgap film is required to withstand such high-temperature operations. However, there is a correlation between band gap and heat resistance, and the larger (wider) the band gap, the more it can withstand high-temperature operation. As mentioned above, it is desirable that the a-Si film has a wide band gap of at least 1.6 eV.
If this is too wide and exceeds 3 eV, it will enter the insulator region and the range of use will be limited, so the upper limit is preferably about 2.5 eV or less. In other words, widening the band gap of the a-Si film,
In addition, it is desired to control the light within the above-mentioned appropriate range depending on the purpose of use or the characteristics of the target light. In view of the above points, the inventors of the present invention have conducted intensive studies and found that chemical vapor deposition (a method in which a gas such as silane is thermally decomposed and deposited on a substrate), which is widely used to form an a-Si film. , Chemical Vapor
In deposition (hereinafter referred to as CVD), by adding a specific amount of ammonia (derivative) etc. to the raw material gas, an a-Si film with a wide band gap of about 1.6 to 2.5 eV is formed at low temperature with good controllability. They discovered that it is possible to do this and completed the present invention. That is, according to the present invention, when a high-order silane gas represented by the general formula SinH ₂ n ₊₂ (where n is an integer of n≧2) is thermally decomposed and deposited on a substrate, the silane gas is In the expression () (In the formula, R ¹ , R ² , R ³ represent a hydrogen atom, an alkyl group, or an aryl group) Ammonia (derivative) and/or represented by the formula () (In the formula, R ⁴ , R ⁵ , R ⁶ , R ⁷ represent a hydrogen atom, an alkyl group, or an aryl group.) Hydrazine (derivative) represented by 0.5≦N/Si (gram-atom ratio) (where where N is ammonia (derivative) and/or hydrazine (derivative) brought into the pyrolysis system.
A method for forming an amorphous silicon film characterized by allowing the presence of amorphous silicon (Si indicates the amount of nitrogen in the high-order silane gas, and Si indicates the amount of silicon in the high-order silane gas). is provided. The present invention will be explained in detail below. The higher-order silane in the present invention is represented by the general formula SinH ₂ n ₊₂ (where n is an integer of n≧2), and includes, for example, disilane (Si ₂ H ₆ ), trisilane (Si ₃ H ₈ ) , tetrasilane (Si ₄ H ₁₀ ), pentasilane (Si ₅ H ₁₂ ), hexasilane (Si ₆ H ₁₄ ), etc., but disilane, trisilane, and tetrasilane are preferred from the viewpoint of ease of handling. These may be used alone or in mixtures. In addition, when using higher-order silane as a mixture, it goes without saying that a small amount of monosilane (SiH ₄ ) may be contained. However,
When only monosilane is used instead of higher-order silane, the decomposition temperature is high and requires a high temperature of 600°C or higher, so the material of the substrate on which a-Si is deposited is limited to expensive quartz glass, sapphire, etc. and lacks practicality. The present invention uses such high-order silane as a raw material to form an amorphous silicon film on a substrate by a thermal decomposition method known per se. At that time, ammonia (derivative) and/or hydrazine (derivative) are heated It is characterized by being added to the decomposition reaction system. Ammonia (derivative) used in the present invention is represented by the formula (), These R ¹ , R ² , R ³ are hydrogen: methyl, ethyl, i
-propyl, n-propyl, i-butyl, sec-
Alkyl groups such as butyl, n-butyl, pentyl, etc.:
Or it represents an aryl group such as phenyl, tolyl, xylyl, naphthyl, etc. Examples of ammonia (derivatives) of formula () include ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, dimethylethylamine, diethylamine, triethylamine, i-propylamine, n
-propylamine, aniline, N-methylaniline, N,N-dimethylaniline, toluidine, xylidine, benzylamine, diphenylamine,
Examples include naphthylamine. In addition, hydrazine (derivative) is represented by the formula (), These R ⁴ , R ⁵ , R ⁶ , R ⁷ are hydrogen: methyl, ethyl, i-propyl, n-propyl, i-butyl,
An alkyl group such as sec-butyl, n-butyl, or pentyl; or an aryl group such as phenyl, tolyl, xylyl, or naphthyl. Examples of hydrazine derivatives of formula () include hydrazine, methylhydrazine, ethylhydrazine, isopropylhydrazine, phenylhydrazine, benzylhydrazine, naphthylhydrazine,
Examples include N,N'-dimethylhydrazine, N,N'-diethylhydrazine, N-methyl-N'-phenylhydrazine, and N,N'-diphenylhydrazine. Among the above-mentioned examples, ammonia is the most preferred in terms of ease of handling and its effects. In addition, other nitrogen compounds such as ethylenediamine, ethanolamine, diethanolamine, triethanolamine, phenylenediamine, and nitroaniline can also be used. Nitrogen amount N in ammonia (derivative) and/or hydrazine (derivative) added to the pyrolysis system
(gram-atom) and the amount of silicon Si (gram-atom) in the raw material high-order silane gas must satisfy the relationship 0.5≦N/Si. If the N/Si ratio is less than 0.5, there is little effect of increasing the band gap value of the a-Si film.
Note that if the N/Si ratio is in the range of 0.5, the band gap value will increase as the N/Si ratio increases, but if N/Si exceeds 1.5, the band gap will increase further as the N/Si ratio increases. Even if the value is increased, the band gap does not increase significantly any further, so it is not economical to use more ammonia (derivatives) or the like than necessary. In the present invention, the pyrolysis pressure may be any pressure including reduced pressure, normal pressure, and atmospheric pressure. It should be noted that it is convenient to carry out thermal decomposition at a pressure higher than atmospheric pressure because the growth rate of the film is originally high, but in that case, the purpose of the present invention can be sufficiently achieved within the range of 2 kg/cm ² -G or less. . Of course, there is nothing wrong with operating under pressure greater than this. In addition, the thermal decomposition temperature in the present invention is 250°C to 600°C.
℃, preferably in the range of 300 to 500℃. If the decomposition temperature exceeds 600° C., an expensive substrate is required and hydrogen is difficult to be incorporated into the a-Si film, making it impossible to obtain sufficient characteristics. In order to obtain sufficient properties, post-treatment to incorporate hydrogen is necessary. Also, if this is less than 250℃,
The decomposition rate of higher-order silane becomes slow, and the growth rate of the a-Si film becomes unsuitable for practical use. As an apparatus for carrying out the present invention, for example, the apparatus shown in FIG. 1 can be used. 10 is a decomposition furnace (reaction tube), 30mmφ×500
It is a quartz glass tube of about mm~60mmφ×1000mm. This may be a rectangular shape (duct) instead of a pipe. The reaction tube has a heater 2 such as a halogen lamp around the outside.
It is equipped with 0. The part of the tube corresponding to the heater is the decomposition zone, and the silicon susceptor 30
(support stand) and quartz glass on the susceptor,
A substrate 40 made of silicon, sapphire, SUS, etc. is set. The temperature in the decomposition zone is measured by thermocouple 45
It is measured by One end of the reaction tube is a raw material gas supply section 50, which supplies high-order silane gas 60, carrier gas 70, and gas 8 such as ammonia (derivative).
0 piping section. 61, 71, 81 are valves, and 63, 73, 83 are gas flow meters. Further, the other end of the reaction tube is an outlet section 90 for exhaust gas. Naturally, the heater 20 is not a lamp heating type, but may be a resistance heating type that heats the entire reaction tube. Note that ammonia (derivatives), etc., can be supplied as a gas alone through piping in the same way as higher-order silane gas if it is gaseous at room temperature, such as ammonia or methylamine, or can be easily gasified, but hydrazine, methylamine, etc. It is preferable that a liquid substance with a slightly high boiling point, such as aniline, be bubbled with a carrier gas such as N ₂ or Ne (not shown) to carry out a diffusion operation, and then be entrained in the carrier gas and supplied to the thermal decomposition system. Next, to explain the decomposition operation, the temperature of the decomposition furnace is raised to above the decomposition temperature, nitrogen gas is flowed and a baking operation is performed, and then the temperature is lowered to the decomposition temperature and the
Temperature stabilize at °C. After that, higher silane
100%, or 0.1 to 20% diluted with an inert gas such as nitrogen, helium, argon, hydrogen, etc., or ammonia (derivative), etc., as is or with a carrier gas of the above inert gas. The high-order silane gas is thermally decomposed by supplying it to a decomposition furnace set at a decomposition temperature of 600°C and depositing a
-Deposit the Si film. Hereinafter, the present invention will be specifically explained with reference to Examples. The a-Si films obtained in the following examples were analyzed and evaluated as follows. (1) Film thickness Depending on the film thickness, the thickness was determined using a combination of the gravimetric method, the method using a surface roughness meter, and the method determined from interference using transmittance. The film growth rate (Å/min) is calculated from this film thickness and thermal decomposition time. (2) Optical band gap Measured using a JASCO CT-50 diffraction grating spectrometer. The absorption coefficient was determined from the transmittance, and the point where the linear part of the absorption coefficient curve was extended and intersected with the photon energy was defined as the optical bandgap. Example 1 The apparatus shown in FIG. 1 was used as an experimental apparatus (reaction tube: 40 mmφ x 600 mm). Source gas containing 1% Si ₂ H ₆ diluted with N ₂ gas at 500c.c./min
Gas containing 10% ammonia diluted with H _{2 50}
cc/min (N/Si=0.5), using _N2 gas as a carrier gas (flow rate 1000c.c./min), pressure 0.5
Kg/cm ² -G is passed through a decomposition furnace and thermally decomposed at 400℃ for 30 minutes.
I went for a minute. Examples 2 to 6 Experiments similar to those in Example 1 were conducted under the conditions shown in Table 1. The results are summarized in Table 1. Comparative Examples 1 to 4 Experiments similar to those in Example 1 were conducted under the conditions shown in Table 2. The results are summarized in Table 2.

【table】

[Table] As is clear from the table, a-Si film with a wide band gap (1.6eV to 2.5eV) can be controlled by adding 0.5≦N/Si of ammonia (derivative) gas in CVD using high-order silane gas. It can be seen that it is well formed. Note that there was almost no difference in the film growth rate (Å/min) compared to the case where no ammonia (derivative) gas was added. As described above, the a-Si film obtained according to the present invention can be suitably put to practical use as a solar cell, an electrophotographic photoreceptor, an image pickup tube device, and a heat-resistant transistor.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an apparatus for carrying out the present invention.

Claims (1)

[Claims] 1. When a high-order silane gas represented by the general formula SinH ₂ n ₊₂ (where n is an integer of n≧2) is thermally decomposed and deposited on a substrate, a , expression () (In the formula, R ¹ , R ² , R ₃ represent a hydrogen atom, an alkyl group, or an aryl group) Ammonia (derivative) and/or represented by the formula () (In the formula, R ⁴ , R ⁵ , R ⁶ , R ⁷ represent a hydrogen atom, an alkyl group, or an aryl group.) Hydrazine (derivative) represented by 0.5≦N/Si (gram-atom ratio) (where where N is ammonia (derivative) and/or hydrazine (derivative) brought into the pyrolysis system.
A method for forming an amorphous silicon film characterized by allowing the presence of amorphous silicon (Si indicates the amount of nitrogen in the high-order silane gas, and Si indicates the amount of silicon in the high-order silane gas).