| abstract |
A semiconductor device for high power applications is provided in which a novel semiconductor material having high mass productivity is provided. After the oxide semiconductor film is formed, a first heat treatment is performed on the exposed oxide semiconductor film in order to reduce impurities such as moisture and hydrogen in the oxide semiconductor film. Next, in order to further reduce impurities such as moisture and hydrogen in the oxide semiconductor film, oxygen is added to the oxide semiconductor film by an ion implantation method, an ion doping method, and the like. Thereafter, the exposed second oxide film is subjected to a second heat treatment . |