Semiconductor device and method for manufacturing semiconductor device

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

• forming a gate electrode layer;
• forming a gate insulating film over the gate electrode layer;
• forming an oxide semiconductor film over the gate insulating film in a region overlapping with the gate electrode layer;
• processing the oxide semiconductor film into an island-shaped oxide semiconductor layer;
• forming source and drain electrode layers electrically connected to the island-shaped oxide semiconductor layer;
• and
• forming an oxide insulating film containing nitrogen over the island-shaped oxide semiconductor layer and the source and drain electrode layers, wherein the oxide insulating film is in contact with the island-shaped oxide semiconductor layer,
• wherein a spin density of the island-shaped oxide semiconductor layer is lower than or equal to 1×1018 spins/cm3.

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

• forming a gate electrode layer over a substrate;
• forming a gate insulating film over the gate electrode layer;
• and
• forming an oxide semiconductor film over the gate insulating film in a region overlapping with the gate electrode layer by a sputtering method using an oxide target comprising indium, gallium, and zinc while heating the substrate,
• wherein the oxide semiconductor film is a c-axis aligned crystalline oxide semiconductor layer, and
• wherein a spin density of the oxide semiconductor film is lower than or equal to 1×1018 spins/cm3.