US Patent 7572685 Method of manufacturing thin film transistor

On a glass substrate, an insulating protective layer comprising SiO2 film is formed, and an active layer comprising a p-Si film is formed thereon. Further, a first gat insulating film comprising an SiN film which serves as a lower layer and a second gate insulating film comprising an SiN film which serves as an upper layer are stacked thereon. The second gate insulating layer is then removed by etching with a gate electrode formed thereon acting as a mask. Thus, ions can be doped only through the first gate insulating film to the p-Si film with a low acceleration energy.