JPS62284080A - Optical deposition method - Google Patents

Abstract

PURPOSE:To continue optical CVD for a long time without reducing the light tansmittance of a window by optically etching the deposit on the light radiating window during the optical CVD process. CONSTITUTION:The raw gas such as Si2H4 is photochemically decomposed by a low-pressure mercury lamp 6, and a thin film of amorphous silicon, etc., is formed on a substrate 1 of Si, etc. In this case, an etching gas such as Cl2 which reacts with the thin film deposit on the incident window 8 for transmitting the light of the lamp 6 to form a volatile compd. is blown from a nozzle 11 on the window 8. The light such as XeC laser 9 as the light source which activates and excites the gaseous Cl2, etc., to promote the reaction with the deposit is radiated through a side window 10. CVD is thus performed while optically etching the deposit on the incident window 8 with the gaseous Cl2, etc., and CVD can be carried out while keeping the deposition rate constant for a long time.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for preventing deposition on a light entrance window in a photo-CVD apparatus.

[Conventional technology and its problems]

In a photo-CVD apparatus, a substrate is placed in a reaction chamber, a source gas is introduced, and light that decomposes the source gas is incident through an entrance window to deposit the decomposed substance on the substrate. In such a photo-CVD apparatus, as the growth time becomes longer,
Deposition proceeds not only on the substrate where this undergrowth should occur, but also on the light entrance window. This deposit significantly reduces the incident light transmission of the entrance window. Therefore, in long-term CVD, the intensity of the incident light, which is the energy source for film formation, gradually weakens, resulting in a decrease in the deposition rate. Conventionally, a method to avoid this has been to spray an inert gas onto the entrance window. This method aims to reduce the probability that the CVD source gas will reach the vicinity of the window by actively sending an inert gas to the surface of the entrance window, thereby preventing photodecomposition of the CVD source gas on the window. Although this method can reduce the rate of deposits on the window,
It is impossible to completely avoid raw material gas getting around the window.
If CVD is carried out for a long time, the influence of deposits on the window cannot be avoided. As an improvement on this method, a method of forming a window with a double structure was announced by Numazawa et al. in a paper with lecture number 1-322 in the proceedings of the 1960 Spring National Conference of the Institute of Electronics and Communication Engineers. In this method, in order to reduce the flow of raw material waste into the vicinity of the window, a second window is installed between the window and the substrate to prevent CVD gas from flowing toward the window. Inert gas is flowing through. Further, the second window is provided with fine holes on its entire surface so that the inert gas can diffuse through the surface of the second window. If this method is used, the deposition rate on the window is further reduced, but the influence of the CVD source gas cannot be avoided in long-time CVD. An object of the present invention is to provide a photodeposition method that solves these conventional problems.

[Means for solving problems]

In order to solve the problem mentioned in item 1, the photodeposition method of the present invention is characterized by using the following means. Etching gas that reacts with deposits from the film-forming raw material gas adhering to the light-incidence window attached to a light-based film-forming apparatus to generate volatile compounds is blown onto the light-incidence window, and the etching gas is It is characterized by being activated using light.

[Effect]

In the present invention, by utilizing the fact that deposits produced by CVD react with an activated specific gas to become a volatile compound and detach from the deposition substrate, the deposits generated in the photo-CVD process on the entrance window are removed from the window. CVD is performed by spraying an etching gas that reacts with the deposits on the groin to produce volatile compounds.
A light source is used to activate this gas and cause the deposits on the window to escape from the window as volatile compounds. If the etching gas is difficult to activate or cannot be activated by the CVD light source, light irradiation with a specific wavelength is separately used to accelerate the reaction and remove the deposits from the entrance window material.

〔Example〕

Embodiments in which the present invention is applied to the growth of amorphous silicon by photo-CVD will be described below in detail with reference to the drawings.

This embodiment is an embodiment in which the etching gas is activated using light other than the excitation light source. The apparatus used in the present invention is an optical CVD apparatus that uses a low-pressure mercury lamp 6 as an excitation source for film formation, and a nozzle 11 for spraying C12 gas onto the entrance window. CI! xecp laser beam irradiation for z gas activation Light irradiation side window L side 1 window side chamber Separation barrier for separating the chambers 7. It is characterized by having a rotary pump 3 for the window side chamber to prevent Ce2 gas in the window side chamber from entering the reaction chamber. In the figure, disilane Si2
H4 is a low pressure mercury lamp (1, 85mm, 254mm>
6 to form an amorphous silicon film on the Si substrate 1. At this time, in order to avoid amorphous silicon from being deposited on the synthetic quartz entrance window 8 for irradiation with the low-pressure mercury lamp 6, the C12 gas is injected into the nozzle 1.
1 onto the entrance window 8. In addition, the C12 gas was irradiated through the side window 10 with light from an x, cgl laser having an oscillation wavelength in the absorption wavelength of the Ce2 gas as a light source for activating the C12 gas and bringing it into an excited state to promote reaction with amorphous silicon. . Further, in order to prevent the C12 gas from leaking onto the Si substrate 1, a separation barrier 7 is provided between the entrance window 8 and the Si substrate 1, and the window side chamber 5 and the reaction chamber 2 are evacuated separately. At this time, the pressure in the window side chamber 5 is set to be lower than that in the reaction chamber 2 in order to prevent Cf2 gas from entering the substrate. For this reason, the rotary pump 3 for the window side chamber was selected to have a higher pumping speed than the rotary pump 4 for the reaction chamber.

The amorphous silicon deposited on the inner wall of the entrance window 8 is C1
By performing CVD before photo-etching using two gases, it was possible to perform CVD while keeping the deposition rate constant for several hours. Since the entrance window 8 is made of quartz, the Cl 2 gas, x, and cpl lasers are not etched, so no damage was caused even during long-time CVD. Also,
There was almost no influence of Cl 2 gas entering the substrate, and the quality of the formed amorphous silicon film was comparable to that when an inert gas was used for spraying the window material. In this example, C! Although Xe I laser is used to activate 2 gases, it does not necessarily have to be XeC! It is not necessary to use a laser beam, and a low-pressure mercury lamp 254 type, which is a CVD excitation source, may be used. However, in this case, the etching efficiency is XeC! It is lower than that of laser.

〔Effect of the invention〕

As explained above, according to the present invention, during the photo-CVD process, deposits on the light irradiation window are photo-etched at the same time, so that the photo-CVD can be carried out for a long time without reducing the transmittance of the window. It is possible to do this.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram 1 showing one embodiment to which the present invention is applied...
Si substrate, 2... reaction chamber, 3... rotary pump for window side chamber, 4... rotary pump for reaction chamber, 5...
window side room, 6... low pressure mercury lamp, 7... separation barrier,
8... Entrance window, 9... xecp laser, 10...
Side wall, 11... nozzle. 71

Claims (1)

[Claims] In the photodeposition method, a thin film is deposited on the substrate by installing a substrate in a reaction chamber, introducing a source gas onto the substrate, and allowing light to decompose the source gas from outside to enter through a window of the reaction chamber to deposit a thin film on the substrate. A photodeposition method characterized in that an etching gas that reacts with deposits adhering to the window to generate a volatile compound is sprayed onto a light incident window of the window, and light that activates the etching gas is introduced.