Semiconductor device and method for manufacturing the same

A semiconductor device comprising:

• a gate electrode over a substrate having an insulating surface;
• a first insulating film over the gate electrode;
• an oxide semiconductor layer including silicon oxide over the first insulating film;
• a second insulating film over the oxide semiconductor layer;
• and
• a source electrode and a drain electrode over the second insulating film,
• wherein the source electrode and the drain electrode are each electrically connected to the oxide semiconductor layer through an opening provided in the second insulating film,
• wherein the first insulating film and the second insulating film each comprise silicon and at least one of oxygen and nitrogen elements, and
• wherein a channel formation region of the oxide semiconductor layer is interposed between the first insulating film and the second insulating film.

A method for manufacturing a semiconductor device, comprising the steps of:

• forming a gate electrode over a substrate having an insulating surface;
• forming a first insulating film comprising a silicon oxynitride film over the gate electrode;
• forming an oxide semiconductor layer over the first insulating film in an atmosphere comprising oxygen;
• stacking a second insulating film comprising a silicon oxynitride film over the oxide semiconductor layer;
• selectively etching the second insulating film to form a protective film;
• selectively etching the oxide semiconductor layer with the use of the protective film as a mask to form an island-like semiconductor layer;
• selectively etching part of the protective film to form a first and a second openings through the protective film;
• forming a conductive film over the protective film and an exposed portion of the island-like semiconductor layer in the first and the second openings;
• and
• selectively etching the conductive film to form a source electrode and a drain electrode.

A method for manufacturing a semiconductor device, comprising the steps of:

• forming a gate electrode over a substrate having an insulating surface;
• forming a first insulating film comprising silicon and at least one of nitride and oxygen over the gate electrode;
• forming an oxide semiconductor layer over the first insulating film in an atmosphere comprising oxygen;
• stacking a second insulating film comprising silicon and at least one of nitride and oxygen over the oxide semiconductor layer;
• and
• forming a source electrode and a drain electrode over the second insulating film,
• wherein the source electrode and the drain electrode are in contact with the oxide semiconductor layer through at least one opening in the second insulating film.