Manufacturing method of semiconductor device

A manufacturing method of a semiconductor device comprising:

• forming an oxide semiconductor layer wherein the oxide semiconductor layer comprises an oxide including crystals having c-axis alignment;
• forming a protective conductive film over the oxide semiconductor layer;
• forming a conductive film over the protective conductive film;
• selectively etching the conductive film under a condition that a first etching selectivity of the conductive film to the protective conductive film is greater than 1, so that the protective conductive film is exposed;
• selectively etching the protective conductive film under a condition that a second etching selectivity of the protective conductive film to the oxide semiconductor layer is greater than 1, so that the oxide semiconductor layer is exposed;
• and
• forming a gate electrode layer over the oxide semiconductor layer.

A manufacturing method of a semiconductor device comprising:

• forming an oxide semiconductor layer wherein the oxide semiconductor layer comprises an oxide including crystals having c-axis alignment;
• forming a first conductive film over the oxide semiconductor layer;
• forming a second conductive film over the first conductive film;
• selectively etching the second conductive film under a condition that a first etching selectivity of the second conductive film to the first conductive film is greater than 1,so that the first conductive film is exposed;
• selectively etching the first conductive film under a condition that a second etching selectivity of the first conductive film to the oxide semiconductor layer is greater than 1, so that the oxide semiconductor layer is exposed;
• and
• forming an insulating layer and an electrode layer over the oxide semiconductor layer so that the insulating layer is interposed between the oxide semiconductor layer and the electrode layer.