Semiconductor device and manufacturing method thereof

A method for manufacturing a semiconductor device comprising:

• forming a gate electrode over a substrate;
• forming a gate insulating film over the gate electrode;
• forming an oxide semiconductor layer containing indium and zinc over the gate insulating film;
• forming a second insulating film comprising silicon oxide over the oxide semiconductor layer;
• forming a channel protective layer over a channel formation region of the oxide semiconductor layer by selectively etching the second insulating film;
• and
• forming a conductive film over the oxide semiconductor layer,
• wherein each of the gate insulating film, the oxide semiconductor layer and the second insulating film is formed by sputtering in an atmosphere containing oxygen at 90% or more.

A method for manufacturing a semiconductor device comprising:

• forming a gate electrode over a substrate;
• forming a gate insulating film over the gate electrode;
• forming an oxide semiconductor layer containing indium and zinc over the gate insulating film;
• forming a second insulating film comprising silicon oxide over the oxide semiconductor layer;
• forming a channel protective layer over a channel formation region of the oxide semiconductor layer by selectively etching the second insulating film;
• and
• forming a conductive film over the oxide semiconductor layer,
• wherein the oxide semiconductor layer is formed by sputtering in an atmosphere containing oxygen at 90% or more.