Patent ID: 8293661

Claim:
A method for manufacturing a semiconductor device, comprising the steps of: forming a gate electrode layer over a substrate having an insulating surface; forming a first oxide insulating layer which covers the gate electrode layer; forming a first oxide semiconductor layer over the gate electrode layer and the first oxide insulating layer; performing first heat treatment so as to form a crystal region in which c-axis is aligned in a direction substantially perpendicular to a surface of the first oxide semiconductor layer; forming a second oxide semiconductor layer over the first oxide semiconductor layer; performing second heat treatment so as to crystallize at least a part of the second oxide semiconductor layer by causing crystal growth from the crystal region; forming a source electrode layer and a drain electrode layer over the second oxide semiconductor layer; forming a second oxide insulating layer which covers the second oxide semiconductor layer, the source electrode layer, and the drain electrode layer; performing third heat treatment so as to supply oxygen to the second oxide semiconductor layer; forming a nitride insulating layer containing hydrogen over the second oxide insulating layer; and performing fourth heat treatment so as to supply hydrogen at least to an interface between the first oxide semiconductor layer and the first oxide insulating layer.