Semiconductor device and method for manufacturing the same

A method for manufacturing a semiconductor device comprising:

• forming a gate electrode over an insulating surface;
• forming an insulating layer over the gate electrode;
• forming an oxide semiconductor layer including silicon oxide over the insulating layer by a sputtering method using a first oxide semiconductor target including silicon oxide at 2.5 wt % to 20 wt % inclusive;
• and
• forming an oxynitride layer over the oxide semiconductor layer including silicon oxide in an atmosphere including nitrogen using a second oxide semiconductor target.

A method for manufacturing a semiconductor device comprising:

• forming an oxide semiconductor layer over an insulating surface by a sputtering method using a first oxide semiconductor target including silicon oxide at 2.5 wt % to 20 wt % inclusive;
• forming an oxynitride layer over the oxide semiconductor layer including silicon oxide by a sputtering method using a second oxide semiconductor target in an atmosphere including nitrogen;
• forming an insulating layer covering the oxynitride layer;
• and
• forming a gate electrode over the insulating layer.