Silicon Carbide Semiconductor Device and Manufacturing Method Thereof

A method of manufacturing a silicon carbide semiconductor device, comprising:

• preparing a silicon carbide substrate which includes a semiconductor layer located over a semiconductor substrate comprising silicon carbide, wherein the semiconductor layer contains a first concentration of an impurity of a first conductivity type, and the semiconductor substrate contains a second concentration of an impurity of the first conductivity type, the first concentration being less than the second concentration, and wherein an upper surface of the silicon carbide substrate defines a cell forming area and an outer peripheral area;
• diffusing an impurity of a second conductivity type into an upper surface of the cell forming area of the semiconductor layer to form a plurality of well regions in the cell forming area of the semiconductor layer, wherein the second conductivity type is opposite the first conductivity type;
• diffusing an impurity of the first conductivity type into the upper surface of the semiconductor layer within the well regions to form source layers within the respective well regions;
• forming an amorphous layer in the semiconductor layer at a boundary between the cell forming area and the outer peripheral area;
• forming an outer peripheral insulating film over the semiconductor layer in the outer peripheral area;
• thermally oxidizing the upper surface of the semiconductor layer in the cell forming area and at least a portion of the amorphous layer exposed by the outer peripheral insulating film to form a gate oxide film including a stepped portion of increased thickness adjacent the outer peripheral insulating film;
• and
• forming a gate electrode layer extends from the gate oxide film to above the outer peripheral insulating film.