Patent ID: 8293594

Claim:
A method for manufacturing a semiconductor device, comprising the steps of: forming a first gate electrode layer and a second gate electrode layer over a substrate, wherein the first gate electrode layer is located in a pixel portion and the second gate electrode layer is located in a driver circuit portion; forming a gate insulating layer over the first gate electrode layer and the second gate electrode layer; forming a first source electrode layer and a first drain electrode layer over the gate insulating layer, wherein the first source electrode layer and the first drain electrode layer overlap with the first gate electrode layer; forming an oxide semiconductor layer over the gate insulating layer, the first source electrode layer and the first drain electrode layer; performing first heat treatment on the oxide semiconductor layer; forming a metal film over the oxide semiconductor layer; selectively etching the oxide semiconductor layer and the metal film to form a first oxide semiconductor layer and a first metal film, which overlap with the first gate electrode layer, and a second oxide semiconductor layer, a second source electrode layer and a second drain electrode layer, which overlap with the second gate electrode layer; removing the first metal film; forming an oxide insulating layer over the first oxide semiconductor layer, the second source electrode layer and the second drain electrode layer; and forming a pixel electrode layer electrically connected to one of the first source electrode layer and the first drain electrode layer, and a conductive layer overlapping with the second oxide semiconductor layer over the oxide insulating layer.