There is provided a technique to form a single crystal semiconductor thin film
or a substantially single crystal semiconductor thin film. An amorphous semiconductor
thin film is irradiated with ultraviolet light or infrared light, to obtain a crystalline
semiconductor thin film (102). Then, the crystalline semiconductor thin
film (102) is subjected to a heat treatment at a temperature of 900 to 1200
C. in a reducing atmosphere. The surface of the crystalline semiconductor thin
film is extremely flattened through this step, defects in crystal grains and crystal
grain boundaries disappear, and the single crystal semiconductor thin film or substantially
single crystal semiconductor thin film is obtained.
