Semiconductor device and method for manufacturing the same

A method for manufacturing a semiconductor device comprising:nforming a gate electrode over a substrate;forming a gate insulating film over the gate electrode;forming an oxide semiconductor layer over the gate insulating film, which contains indium, gallium, and zinc and overlaps with the gate electrode;forming buffer layers over the oxide semiconductor layer and a first electrode and a second electrode over the buffer layers,wherein the buffer layers are formed in such a manner that a target which includes, as its component, an oxide containing indium, gallium, and zinc is sputtered in an atmosphere including a nitrogen gas.

A method for manufacturing a semiconductor device comprising:nforming a gate electrode over a substrate;forming a gate insulating film over the gate electrode;forming a first electrode and a second electrode over the gate insulating film, whose end portions overlap with the gate electrode;forming buffer layers over the first electrode and the second electrode and an oxide semiconductor layer containing indium, gallium, and zinc over the buffer layers,wherein the buffer layers are formed in such a manner that a target which includes, as its component, an oxide containing indium, gallium, and zinc is sputtered in an atmosphere including a nitrogen gas.

A method for manufacturing a semiconductor device comprising:nforming a gate electrode over a substrate;forming a gate insulating film over the gate electrode;forming an oxide semiconductor layer over the gate insulating film, which contains indium, gallium, and zinc and overlaps with the gate electrode;sputtering a target including, as its component, an oxide containing indium, gallium, and zinc in an atmosphere including a nitrogen gas to form an oxynitride film;forming a conductive film over the oxynitride film; andetching the conductive film and the oxynitride film to form buffer layers over the oxide semiconductor layer and a first electrode and a second electrode over the buffer layers.