By applying ion or optical energy or catalytic effects at the time of depositing a crystalline silicon thin film, improvements in crystallinity of the crystalline silicon thin film in proximities of an interface of a substrate or smoothing of its surface may be achieved. With this arrangement, it is possible to achieve improvements in crystallinity of the crystalline silicon film that is formed in a low temperature condition through CVD method and to prevent concaves and convexes from being formed on its surface or to prevent oxidation of grain fields, and it is accordingly possible to provide a thin film transistor, a semiconductor device such as a solar cell and methods for manufacturing these that exhibit superior characteristics and reliability.