Semiconductor device and method for manufacturing the same

A method for manufacturing a semiconductor device comprising:

• forming a first oxide semiconductor layer by a sputtering method;
• crystallizing a region of the first oxide semiconductor layer by a first heat treatment, the region including a surface of the first oxide semiconductor layer;
• forming a second oxide semiconductor layer over the first oxide semiconductor layer by a sputtering method;
• crystallizing the second oxide semiconductor layer by a second heat treatment;
• wherein the second oxide semiconductor layer includes In, Ga, and Zn, and
• wherein the second oxide semiconductor layer includes a crystal whose c-axis is aligned in a direction perpendicular to a surface of the second oxide semiconductor layer.

A semiconductor device comprising:

• a first oxide semiconductor layer;
• and
• a second oxide semiconductor layer over the first oxide semiconductor layer,
• wherein the second oxide semiconductor layer includes In, Ga, and Zn,
• wherein the first oxide semiconductor layer is a first non-single crystalline layer including a crystal, and
• wherein the second oxide semiconductor layer is a second non-single crystalline layer including a crystal whose c-axis is aligned in a direction perpendicular to a surface of the second oxide semiconductor layer.