Method for manufacturing semiconductor device

A semiconductor device comprising:

• a gate electrode;
• an insulating layer over the gate electrode, the insulating layer comprising silicon and excessive oxygen;
• an oxide semiconductor layer over the gate electrode, the oxide semiconductor layer including a channel formation region and being in contact with the insulating layer;
• and
• a channel protective layer over the oxide semiconductor layer.

A semiconductor device comprising:

• an insulating layer comprising silicon and oxygen;
• an oxide semiconductor layer in contact with the insulating layer, the oxide semiconductor layer including a channel formation region;
• a gate electrode adjacent to the oxide semiconductor layer;
• a first n-type conductivity region;
• a second n-type conductivity region;
• a source electrode comprising a first metal layer over the first n-type conductivity region, wherein the source electrode is in electrical contact with the channel formation region of the oxide semiconductor layer through the first n-type conductivity region;
• and
• a drain electrode comprising a second metal layer over the second n-type conductivity region, wherein the drain electrode is in electrical contact with the channel formation region of the oxide semiconductor layer through the second n-type conductivity region,
• wherein the oxide semiconductor layer contains excessive oxygen.

A semiconductor device comprising:

• a gate electrode;
• an insulating layer over the gate electrode, the insulating layer comprising silicon and oxygen;
• an oxide semiconductor layer over the gate electrode, the oxide semiconductor layer including a channel formation region and being in contact with the insulating layer;
• and
• a channel protective layer over the oxide semiconductor layer,
• wherein the oxide semiconductor layer contains excessive oxygen.