Semiconductor device with carbon-density-decreasing region

A semiconductor device comprising:

• an SiC semiconductor layer of a first conductivity type;
• a body region of a second conductivity type that is formed in a surface layer portion of the SiC semiconductor layer;
• a source region of the first conductivity type that is formed in a surface layer portion of the body region;
• a trench that is formed in the SiC semiconductor layer such as to penetrate the source region and the body region;
• an SiO2 layer that covers a part of a surface of the SiC semiconductor and a wall surface of the trench, and that has a first surface in contact with the SiC semiconductor layer and a second surface positioned on an opposite side to the first surface;
• a gate electrode that is arranged in the trench via the SiO2 layer;
• and
• an upper insulating layer that covers the second surface of the SiO2 layer and the gate electrode;
• wherein the SiO2 layer has:
• a first surface side region that has a carbon density gradually decreases from not less than 1.0×1022 cm−3 to not more than 4.0×1020 cm−3 from the first surface side to the second surface side;
• and
• a second surface side region that has a carbon density lower than the carbon density of the first surface side region, and that has a thickness of not less than a thickness of the first surface side region.