Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
1999-09-03
2001-12-04
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S681000
Reexamination Certificate
active
06326304
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing an amorphous silicon-based thin film photoelectric conversion device, and particularly to a method of manufacturing thereof to achieve an excellent performance as an amorphous silicon-based thin film photoelectric conversion device together with improvements in production cost and efficiency.
2. Description of the Background Art
An amorphous silicon based solar cell is a typical thin film photoelectric conversion device. An amorphous photoelectric conversion material is usually prepared by a plasma CVD method at a film-forming temperature as low as about 200° C., so that it can be formed on an inexpensive substrate, e.g., of glass, stainless steel, organic film, and thus expected as a preferable material for low-cost photoelectric conversion devices. Furthermore, since amorphous silicon has a large absorption coefficient for the visible-light range, a solar cell using an amorphous photoelectric conversion layer of a thickness at most 500 nm has achieved a short-circuit current at least 15 mA/cm
2
.
A p type semiconductor layer, an i type amorphous photoelectric conversion layer, and an n type semiconductor layer that compose the amorphous silicon-based solar cell are usually produced by plasma CVD respectively and the pressure in a conventional plasma CVD reaction chamber is 1 Torr or less.
U.S. Pat. No. 5,646,050, for example, discloses a method of manufacturing an amorphous silicon-based solar cell under a relatively high pressure condition. According to this document, an amorphous silicon layer in the amorphous silicon-based solar cell is fabricated on conditions that the pressure is greater than 1.0 Torr and at most 10 Torr, and the dilution ratio of dilution gas to raw material gas ranges from 5:1 to 200:1.
If the pressure is 1 Torr or less, the deposition rate decreases.
According to the conditions for depositing the amorphous silicon layer disclosed in U.S. Pat. No. 5,646,050, the amount of the dilution gas relative to the raw material gas is excessive. In other words, the amount of the raw material gas relative to the dilution gas is too small. As a result, the amount of the raw material gas supplied into the plasma CVD reaction chamber is insufficient, leading to degradation of the film deposition rate.
SUMMARY OF THE INVENTION
The present invention is made to solve the problems above. One object of the present invention is to provide a method of manufacturing an amorphous silicon-based thin film photoelectric conversion device having an excellent performance and improve the cost and efficiency in production by enhancing the efficiency in the use of raw material gas (ratio of the reacted gas to the total gas which is supplied into the reaction chamber) and increasing the film deposition rate.
According to a method of manufacturing an amorphous silicon-based thin film photoelectric conversion device in one aspect of the invention, the amorphous silicon-based thin film photoelectric conversion device having a stacked structure composed of a p type semiconductor layer, an i type amorphous silicon-based photoelectric conversion layer, and an n type semiconductor layer is fabricated by plasma CVD. The method is characterized in that at least one layer of the p type semiconductor layer, the i type amorphous silicon-based photoelectric conversion layer, and the n type semiconductor layer is formed on conditions that silane-type gas as a main component of raw material gas which is supplied into a plasma CVD reaction chamber as well as dilution gas containing hydrogen are used, the flow rate of the dilution gas is four or less times that of the silane-type gas, the partial pressure of the silane-type gas in the plasma CVD reaction chamber ranges from 1.2 Torr to 5.0 Torr, and the distance between a surface of a substrate mounted on one electrode and a surface of the other electrode opposed to the one electrode hereinafter referred to simply as “distance between electrodes”) ranges from 8 mm to 15 mm.
According to the method of manufacturing an amorphous silicon-based thin film photoelectric conversion device in the one aspect of the invention, the conditions of the dilution, pressure, and distance between electrodes are defined to be within predetermined ranges such that plasma can efficiently be confined between the electrodes. Accordingly, the film deposition rate is enhanced and the efficiency in the use of the raw material gas such as silane-type gas is improved to reduce the manufacturing cost of the amorphous silicon-based thin film photoelectric conversion device. Further, a resultant performance is similar to that of the photoelectric conversion device (e.g. solar cell) fabricated by the conventional method, and degradation of the photoelectric conversion property due to exposure to the light over a long period, i.e. the rate of light degradation can be reduced.
The condition that the flow rate of the dilution gas is four or less times that of the silane-type gas is defined in order to prevent reduction in amount of the raw material gas within the reaction chamber and thus prevent decrease in film deposition rate as observed in the conventional method if the flow rate is more than four times.
The condition that the partial pressure of the silane-type gas ranges from 1.2 Torr to 5.0 Torr is defined to avoid an insufficient amount of the raw material gas within the reaction chamber leading to decrease in deposition rate as observed if the partial pressure is less than 1.2 Torr, and prevent generation of a large amount of powder-like products and dust within the reaction chamber as observed if the partial pressure exceeds 5.0 Torr.
The condition that the distance between electrodes ranges from 8 mm to 15 mm is defined to avoid difficulty in plasma discharging and in implementing a constant distance between the electrodes over the electrode surfaces and thus prevent nonuniform deposition over the surfaces as observed if the distance is less than 8 mm. If the distance exceeds 15 mm, discharging cannot be maintained.
According to a method of manufacturing an amorphous silicon-based thin film photoelectric conversion device in another aspect of the invention, the amorphous silicon-based thin film photoelectric conversion device having a stacked structure composed of a p type semiconductor layer, an i type amorphous silicon-based photoelectric conversion layer, and an n type semiconductor layer is fabricated by plasma CVD. The method is characterized in that at least one layer of the p type semiconductor layer, the i type amorphous silicon-based photoelectric conversion layer, and the n type semiconductor layer is fabricated on conditions that silane-type gas as a main component of raw material gas which is supplied into a plasma CVD reaction chamber is used without using dilution gas, the partial pressure of the silane-type gas in the plasma CVD reaction chamber ranges from 1.2 Torr to 5.0 Torr, and the distance between a surface of a substrate mounted on one electrode and a surface of the other electrode opposed to the one electrode ranges from 8 mm to 15 mm.
According to the method of manufacturing an amorphous silicon-based thin film photoelectric conversion device in the another aspect of the invention, plasma can efficiently be confined between the electrodes since the conditions of the dilution, pressure, and distance between electrodes are defined to be within predetermined ranges as the one aspect of the invention discussed above. Consequently, the production cost of the amorphous silicon-based thin film photoelectric conversion device can be reduced since the film deposition rate is improved and the efficiency in the use of the raw material gas such as silane-type gas is enhanced. In addition, a resultant performance is almost similar to that of the photoelectric conversion device produced by the conventional method and the rate of light degradation can be reduced.
Enhancement of the film deposition rate is possible since the dilution gas is not used and
Yamamoto Kenji
Yoshimi Masashi
Hogan & Hartson L.L.P.
Kaneka Corporation
Le Dung A
Nelms David
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