Coating processes – Electrical product produced – Welding electrode
Patent
1984-07-06
1986-04-29
Williams, Edward S.
Coating processes
Electrical product produced
Welding electrode
427 36, 427 531, B05D 306
Patent
active
045856710
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a process for forming an amorphous silicon film (hereinafter abbreviated "a-Si film") by photochemical decomposition of a higher silane, and more specifically to a process for forming an a-Si film at a low temperature by conducting such decomposition of a higher silane under radiation of a light having a specific wavelength.
BACKGROUND ART
owing to the excellent optoelectric characteristics of a-Si films, they are used in solar batteries, photosensors for electrophotography, thin-film transistors, optical sensors, etc. As one of fabrication processes of such a-Si films, may be mentioned the so-called chemical vapor deposition process (hereinafter abbreviated to "CVD") in which a gas such as silane is thermally decomposed to deposit amorphous silicon on a substrate. The CVD process has such great merits, compared with the plasma deposition technique, sputtering deposition technique, ion-plating process and the like, that the CVD process may be readily practiced without using complex, expensive and large facilities.
The CVD process is however accompanied by such drawbacks that the materials of substrates, on which a-Si is to be deposited, are limited to expensive metals, silica glass, sapphire or the like because the CVD process requires extremely high temperatures of 600.degree. C. and higher. It is the so-called photochemical vapor deposition process that was proposed with a view toward solving such drawbacks and enabling to practice the CVD process at lower temperatures and has recently been attracting attention. Among such photo CVD processes, the leading one is currently the mercury sensitizing process. This process makes use of the sensitizing effect of mercury (Hg). When Hg vapor is also allowed to exist in a thermal decomposition reaction system and a light is radiated to Hg vapor to excite same ##STR1## transfer of energy is induced to occur between the excited species and the reaction species so that the thermal decomposition reaction may be allowed to proceed. This action of Hg is a sort of catalytic effect and can increase the growth rate of the film by several to several thousands times. Accordingly, an a-Si film can be formed at a relatively low temperature (for example, 400.degree. C. or so) for example in a thermal decomposition reaction of SiH.sub.4.
The mercury sensitizing process involves an inherent problem from the viewpoints of pollution and safety aspects that it requires to use mercury, which is a toxic substance difficult to handle, and moreover to employ it in a vapor form, and it is accompanied by a drawback that it is indispensable to apply a surface treatment and post treatment to resulting a-Si although such treatments are difficult to conduct--(1). Besides, the mercury sensitizing process is accompanied by a serious shortcoming from the practical view point that, since Hg vapor is caused to exist all over the interior of the reactor cylinder, a-Si is allowed to deposit on a window or the like through which a light is introduced into the reactor cylinder and hence gradually deposit there, interferes the introduction of the light and lowers the growth rate rapidly in the course of each decomposition operation, resulting in unavoidable frequent interruption of the operation--(2). In addition, there is a possibility that Hg may be taken in the resulting a-Si film--(3).
DISCLOSURE OF THE INVENTION
An object of this invention is to provide a process which permits to form an a-Si film by the photochemical decomposition of silane without need for any Hg catalyst.
Another object of this invention is to provide a process which enables to form an a-Si film even at a low temperature of 300.degree. C. or lower, that is the thermal decomposition temperature of a higher silane.
The present invention provides the following formation process of an a-Si film:
A process for forming an amorphous silicon film, which process comprises subjecting a gaseous higher silane represented by the following general formula: decomposition under radiation of a li
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"Novel Amorphous Silicon Solar Cells Prepared by Photochemical Vapor Deposition", Saitoh, et al. (Sep. 1982 at Tokyo) Proc. 14th Int. Conf. Solid State Devices.
Ashida Yoshinori
Hirose Masataka
Isogaya Kazuyoshi
Kitagawa Nobuhisa
Mitsui Toatsu Chemicals Incorporated
Williams Edward S.
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