Patent ID: 8207026

Claim:
A method for manufacturing a semiconductor device including a thin film transistor comprising the steps of forming a first conductive film; forming an insulating film over the first conductive film; forming a semiconductor film over the insulating film; forming an impurity semiconductor film over the semiconductor film; forming a second conductive film over the impurity semiconductor film; forming a first resist mask over the second conductive film; performing first etching on the insulating film, the semiconductor film, the impurity semiconductor film, and the second conductive film using the first resist mask to expose at least a surface of the first conductive film; performing an oxidation treatment to oxidize at least a side surface of the semiconductor film and the surface of the first conductive film; performing second etching in which side-etching is performed on part of the first conductive film by dry etching to form a gate electrode layer after performing the oxidation treatment; forming a second resist mask over the second conductive film; and performing third etching on each part of the second conductive film, the impurity semiconductor film, and the semiconductor film using the second resist mask to form a source and drain electrode layer, a source and drain region, and a semiconductor layer.