Patent ID: 8329506

Claim:
A method for manufacturing a semiconductor device comprising the steps of: forming an In—Ga—Zn—O based oxide semiconductor layer having an amorphous structure over a substrate by a sputtering method; heating the In—Ga—Zn—O based oxide semiconductor layer to form an oxide semiconductor layer including crystal grains represented by InGaZnO 4 in the amorphous structure; and forming a channel formation region of a transistor using the oxide semiconductor layer including the crystal grains represented by InGaZnO 4 , wherein a proportion of the amorphous structure in the In—Ga—Zn—O based oxide semiconductor layer is 90 volume % or less after the heating, wherein a proportion of the crystal grains represented by InGaZnO 4 to a whole of crystal grains is 80 volume % or more.