JPH0112836B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an apparatus for producing amorphous silicon, which is attracting attention as a material for solar cells, photoreceptors, and the like. Vacuum deposition, reactive sputtering, ion plating, CVD, plasma CVD, and other methods have been tried to generate amorphous silicon (a-Si), but plasma CVD is generally used. The plasma CVD method uses the direct current bipolar method,
There are two methods: AC capacitive coupling method and AC electromagnetic inductive coupling method. Figure 1 shows the principle of AC capacitive coupling method. Become. Inside the reaction tank 2, which is connected to the exhaust system 1 via a valve 5, there is a-Si.
A support 7 that supports a substrate 6 on which a layer is to be formed and serves as one electrode, and another electrode 8 to which a voltage is applied by the power source 4 are arranged. Also, reaction tank 2
is connected to the gas supply system 3 via a gas inlet 9 and a valve 10. In order to form the a-Si layer, the reaction tank 2 is evacuated to a vacuum level of 10 ^-5 Torr or more, and a reactive gas such as SiH ₄ or a mixed gas with other gases is introduced from the gas inlet ⁹ . The pressure is about 5 Torr, and the base 6 is heated by the heater 11 of the support 7.
It is heated to 100 to 350°C and a radio frequency voltage of 500 to 5000 V is applied between it and the electrode 8 to generate glow discharge. Under these conditions, the reaction gas is decomposed in the glow and reacts on the surface of the base 6 to form a-
A Si:H (amorphous silicon containing hydrogen) film is formed. The deposition rate at this time is 1 to 100 Å/
sec, and the reaction gas utilization efficiency is several percent to 10
It is about %. Therefore, in order to reduce the cost of products using amorphous silicon, especially photoreceptors with thick films, one is to increase the film formation rate and shorten the manufacturing time, and the other is to reduce the manufacturing time. It is very effective to improve the utilization efficiency of reaction gas. BAScott et al. reported that when Si ₂ H ₆ or Si ₃ H ₆ is used instead of SiH ₄ gas as the reaction gas, a film formation rate of about 20 times can be obtained as shown in Table 1. (Applied Physics Letters) (Appl.Phys.
Lett.) Volume 37, No. 8, pp. 725-727).

[Table] Therefore, by changing the reaction gas from SiH ₄ to Si ₂ H ₆ , the photoreceptor film formation time, which conventionally required more than 10 hours, can be shortened to within a few hours. However, at present, it is difficult to obtain Si ₂ H ₆ gas, and even if it were available, it is very expensive, so it is not useful for reducing product costs. As a way to solve this problem, Inoue et al. polymerized SiH ₄ -based gas by silent discharge to synthesize higher-order silicon hydrides than SiH ₄ such as Si ₂ H ₆ and Si ₃ H ₈ , and used this as a reaction gas. He proposed a glow discharge decomposition method (1981 Spring Meeting of the Japan Society of Applied Physics, 1p-S-5).
Figure 2 shows a gas circuit to which this method is applied, in which SiH ₄ gas is passed from a cylinder 12 through a valve 13 to a silent discharge tube 14, a gas pump 15, and a cold trap 1.
The SiH 4 gas is introduced into a closed gas circuit consisting of 6 and circulated there by a pump 15, and a part of the SiH ₄ gas is decomposed and synthesized by a reaction such as 2SiH ₄ →Si ₂ H ₆ +H ₂ in the silent discharge tube 14. ₂ H ₆ or Si ₃ H ₈
system silicon hydride is produced. The generated high-order silicon hydride is captured in the cold trap 16, and after a predetermined capacity has been stored, the residual gas present in this gas circuit is removed. Next, the temperature of the cold trap 16 is raised to gasify the trapped components, which are then passed through the valve 17 together with the carrier Ar gas from the cylinder 18 from the flow path selection and flow path control section 19 as shown in FIG. It is supplied to a similar plasma CVD reaction tank 2. However, this batch processing method is complicated to operate;
This method has drawbacks such as the inability to produce an a-Si film while producing or capturing Si ₂ H ₆ compounds, making it difficult to apply to the production of products such as photoreceptors. The present invention solves the drawbacks in the process of synthesizing higher-order silicon hydrides such as Si ₂ H ₆ from SiH ₄ based compounds by such silent discharge.
It is an object of the present invention to provide an apparatus for synthesizing higher-order silicon hydride by continuous processing without batch processing, and producing amorphous silicon using the same. In order to carry out continuous processing, it is necessary to continuously remove hydrogen produced as a by-product during the above-mentioned chemical reaction. This is because amorphous silicon containing a high concentration of hydrogen has poor photoconductivity. The present invention solves this problem by synthesizing higher-order silicon hydride from SiH ₄ gas between a reaction tank that uses silicon hydride to produce amorphous silicon by plasma CVD and a SiH ₄ gas supply system. The solution was solved by inserting a device and a device for continuously removing hydrogen produced by the synthesis reaction, and the above objective was achieved. The method using silent discharge described above can be applied to synthesize higher-order silicon hydride from SiH ₄ -based gas. In order to continuously remove hydrogen, it is effective to use a hydrogen gas selective permeation membrane. Embodiments of the present invention will be described below with reference to the drawings. In FIG. 3, parts common to those in FIGS. 1 and 2 are given the same reference numerals. cylinder 1
From 2, SiH ₄ gas such as SiH ₄ , SiH ₂ F ₂ , or a mixed gas with other gases is supplied to the gas reformer 2.
0. The gas reformer 20 modifies SiH ₄ -based gas into higher-order SinHm -based compounds, and the main reaction is 2SiH ₄ →Si ₂ H ₆ + in the case of SiH ₄
It is expressed by the formula H ₂ . In addition to the silent discharge method, such reactions can also be induced by the application of short wavelength ultraviolet light (for example, 2537 Å light from a low-pressure mercury lamp). The reformed gas containing a large amount of H ₂ coming out of the reformer 20 is passed through a filter 21 for removing solid content.
The hydrogen is then introduced into the hydrogen removal device 22. The hydrogen removal device 22 is configured to selectively permeate hydrogen gas through a bundle of thin tubes 23 made of a polyimide-based polymer material, as shown in FIG. 4A and FIG. Gas from the filter 21 is introduced into the inlet chamber 24 and reaches the outlet chamber 25 from one end of the bundled hydrogen gas permeable capillaries 23 to the other end. Hydrogen is tube 2
3, the gas permeates through the wall of the pipe 23 and is removed from the system by the connected suction pump 25. Of course, as can be easily surmised, the hydrogen gas selective permeation membrane is not limited to the shape of a thin tube, and a system having the same function can be constructed even if it is shaped like a flat plate. The reformed gas with reduced hydrogen content that has reached the outlet chamber 25 of the hydrogen removal device 22 is subjected to plasma CVD via the valve 10.
The gas is introduced into the gas inlet 9 of the reaction tank 2. The introduced reformed gas is a high-order SinHm such as Si ₂ H ₆ .
Because it contains a high concentration of compounds, it is difficult to use conventional
The film formation rate of a-Si can be greatly improved compared to SiH ₄ based reactive gas. In this case, the supply amount of the reformed gas is controlled by gas flow rate control, gas reformer 2
This can be secured by adopting a zero capacity and a recirculation method. As described above, the present invention is directed to Si ₂ H ₆ which is used to improve the deposition rate of amorphous silicon.
Alternatively, the reactive gas of Si ₃ H ₈ is produced by polymerization using easily available SiH ₄ gas as a raw material, and the
This method forms an amorphous silicon film by the plasma CVD method while removing _H2 gas and continuously supplying a reaction gas with a high concentration of silicon hydride to the reaction tank. It is extremely effective in improving the productivity of amorphous silicon applied devices such as silicon photoreceptors.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an example of an amorphous silicon production device, FIG. 2 is an explanatory diagram showing an example of an amorphous silicon production device having a batch type gas reformer, and FIG. 3 is an explanatory diagram showing an example of an amorphous silicon production device having a batch type gas reformer. FIG. 4 is an explanatory diagram of an amorphous silicon device having a continuous gas reforming device as shown in FIG. 2... Plasma CVD reaction tank, 12... SiH ₄ gas cylinder, 20... Gas reformer, 22... Hydrogen removal device, 23... Hydrogen gas permeable thin tube.

Claims (1)

[Claims] 1. In a device that produces amorphous silicon by plasma CVD using silicon hydride, there _is
An amorphous silicon production device characterized by being equipped with a device for synthesizing a higher-order silicon hydride from _SiH4 -based gas and a device for continuously removing hydrogen produced by the synthesis reaction. 2. In the device according to claim 1,
An amorphous silicon production device characterized in that the device for synthesizing high-order silicon hydride from _SiH4 -based gas uses silent discharge. 3. In the device according to claim 1,
An amorphous silicon production device characterized in that the device for removing hydrogen produced by a synthesis reaction is a hydrogen gas selective permeation membrane.