Patent ID: 8461007

Claim:
A method for manufacturing a semiconductor device, comprising: forming a first insulating film; forming source and drain electrodes over the first insulating film; forming an oxide semiconductor over the first insulating film; performing heat treatment on the oxide semiconductor film so that a hydrogen atom in the oxide semiconductor film is removed; after the heat treatment, performing oxygen doping treatment on the oxide semiconductor film, so that an oxygen atom is supplied into the oxide semiconductor film; after the oxygen doping treatment, forming a second insulating film over the oxide semiconductor film; and forming a gate electrode over the second insulating film so as to overlap with the oxide semiconductor film, wherein the oxygen doping treatment is performed so that the oxide semiconductor film includes an oxygen atom whose proportion is greater than a stoichiometric proportion of the oxide semiconductor film and less than twice the stoichiometric proportion, and wherein the oxide semiconductor layer is electrically connected to the source and drain electrodes.