1. Field of the Invention
The present invention relates to a method of producing a single crystal film. More particularly, it relates to a method of forming a single crystal silicon film on an insulating film by a heat treatment of low temperature.
2. Description of the Prior Art
In the field of the production of semiconductor devices, there has heretofore been extensively employed a technique in which a material required for the formation of a single crystal film is transported onto the surface of a single crystal substrate, and the epitaxial growth is performed on the surface of the single crystal substrate, thereby to form the single crystal film.
On the other hand, the remarkable progress of various semiconductor devices in recent years has led to an eager request for a technique which can form a single crystal film, not only on the single crystal substrate, but also on an amorphous substance such as an insulating film.
As methods of forming a single crystal film on an insulating film, a large number of methods have been proposed. For example, a method has been proposed in which a polycrystalline or amorphous silicon film is irradiated with a powerful laser beam or electron beam to be turned into a single crystal.
With this method, the polycrystalline or amorphous silicon film deposited on an insulating film is melted by irradiating it with the laser beam or electron beam, and the single crystal film is formed on the insulating film by utilizing the liquid phase epitaxy or the grain growth which takes place in the course of the solidification of the melted silicon film.
In the growth of the single crystal film based on the irradiation with the laser beam or the electron beam, however, there are involved such numerous problems, which need to be solved, that the deposited film is deformed, that a strain develops in the deposited film due to a great heat gradient, that the growth conditions of the single crystal are limited, and that since impurity diffusion is caused in the active region of a device by a temperature rise in the vicinity of the melted area, a p-n junction is deformed, so the characteristics of the semiconductor device fluctuate.
On the other hand, a method has been proposed in which a film of a desired substance is deposited on the surface of a single crystal substrate in ultra-high vacuum on the order of, e.g., 10.sup.-7 -10.sup.-11 Torr, whereupon the resultant substrate is heated to turn the film of the substance into a single crystal by the solid phase epitaxial growth.
In this case, the temperature of the heat treatment which is conducted after the deposition of the film may be a comparatively low temperature, and it is said that the single crystal is grown at, for example, 600.degree.-700.degree. C. This method, however, consists in epitaxially growing the single crystal film on the single crystal substrate and does not refer at all to the growth of a single crystal on an amorphous substrate or amorphous film.
As is well known, it is an already established technique to form a single crystal film on a single crystal substrate by the epitaxial growth, and it is this method that has been in extensive practical use in the field of semiconductor device production.
The growth of a single crystal film on an insulator, however, is far more difficult than the growth on the single crystal substrate and has not been put into wide practical use yet.
Obviously, it is very useful in the field of semiconductor device production that a single crystal film can be formed on a film or substrate made of an amorphous substance such as insulator, especially at a comparatively low temperature. Nevertheless, such a method has not been established yet.