Semiconductor device and method for manufacturing thereof

A semiconductor device comprising:

• an insulating layer including a projecting structural body;
• an oxide semiconductor layer in contact with at least a part of a top surface and a side surface of the projecting structural body;
• a gate insulating layer over the oxide semiconductor layer;
• a gate electrode over the gate insulating layer, wherein the gate electrode covers at least a part of the top and the side surfaces of the projecting structural body;
• and
• a source electrode and a drain electrode which are electrically connected to the oxide semiconductor layer,
• wherein the projecting structural body has a curved surface in an upper end corner portion where the top surface and the side surface intersect with each other, and
• wherein the oxide semiconductor layer in the upper end corner portion includes a crystal having a c-axis substantially perpendicular to the curved surface of the upper end corner portion.

A method for manufacturing a semiconductor device, comprising:

• forming an insulating layer including a projecting structural body that includes a curved surface in an upper end corner portion where a top surface of the projecting structural body and a side surface of the projecting structural body intersect with each other;
• forming an oxide semiconductor layer in contact with at least a part of the top surface and the side surface while heat treatment is performed;
• forming a source electrode and a drain electrode adjacent to the oxide semiconductor layer;
• forming a gate insulating layer over the oxide semiconductor layer;
• and
• forming a gate electrode over the gate insulating layer to cover at least a part of the top surface and the side surface.

A method for manufacturing a semiconductor device, comprising:

• forming an insulating layer including a projecting structural body that includes a curved surface in an upper end corner portion where a top surface of the projecting structural body and a side surface of the projecting structural body intersect with each other;
• forming an oxide semiconductor layer having an amorphous state in contact with at least a part of the top surface and the side surface while heat treatment is performed at a temperature lower than 200° C.;
• heating the oxide semiconductor layer at a temperature higher than or equal to 450° C. so that the oxide semiconductor layer includes a crystal having a c-axis substantially perpendicular to the curved surface;
• forming a source electrode and a drain electrode adjacent to the oxide semiconductor layer;
• forming a gate insulating layer over the oxide semiconductor layer;
• and
• forming a gate electrode over the gate insulating layer to cover at least a part of the top surface and the side surface.