Patent ID: 8759132

Claim:
A method for manufacturing a semiconductor device comprising a pixel portion including a first thin film transistor and a driver circuit portion including a second thin film transistor, comprising the steps of: forming a first conductive film over a substrate; forming a second conductive film over the first conductive film, wherein resistance of the second conductive film is lower than that of the first conductive film; forming a first resist mask including a first region and a second region over the second conductive film, wherein the first resist mask is thinner in the first region than in the second region; etching with the use of the first resist mask so that the second conductive film and part of the first conductive film in the pixel portion, and part of the second conductive film and part of the first conductive film in the driver circuit portion are removed, thereby forming a first gate electrode layer of the first thin film transistor and a second gate electrode layer of the second thin film transistor; forming a first gate insulating film over the first gate electrode layer and a second gate insulating film over the second gate electrode layer; forming a first semiconductor layer over the first gate insulating film and a second semiconductor layer over the second gate insulating film; forming a third conductive film over the first semiconductor layer and the second semiconductor layer; forming a fourth conductive film over the third conductive film, wherein resistance of the fourth conductive film is lower than that of the third conductive film; forming a second resist mask including a third region and a fourth region over the fourth conductive film, wherein the second resist mask is thinner in the third region than in the fourth region; and etching with the use of the second resist mask so that part of the third conductive film and the fourth conductive film in the pixel portion, and part of the fourth conductive film and part of the third conductive film in the driver circuit portion are removed, thereby forming a first source electrode layer and a first drain electrode layer over the first gate insulating film, and a second source electrode layer and a second drain electrode layer over the second gate insulating film, wherein the first conductive film and the third conductive film are capable of transmitting light.