Method for manufacturing silicon carbide semiconductor device having trench

A method for manufacturing a silicon carbide semiconductor device comprising steps of:

• preparing a silicon carbide substrate including a first semiconductor layer, a second semiconductor layer, and a third semiconductor layer, said first semiconductor layer having a first conductivity type, said second semiconductor layer being provided on said first semiconductor layer, said second semiconductor layer having a second conductivity type, said third semiconductor layer being provided on said second semiconductor layer, said third semiconductor layer being separated from said first semiconductor layer by said second semiconductor layer, said third semiconductor layer having said first conductivity type;
• forming a trench having an opening in said silicon carbide substrate, said trench including a bottom surface and a side wall surface, said bottom surface being constituted of said first semiconductor layer, said side wall surface having first to third side surfaces respectively constituted of said first to third semiconductor layers, said trench having a corner portion formed by said first side surface and said bottom surface meeting each other;
• forming a corner insulating film to cover said corner portion and expose a region extending from said opening onto said second side surface;
• forming a gate insulating film to cover a region extending from said opening to said corner portion, the step of forming said gate insulating film including a step of thermally oxidizing said trench provided with said corner insulating film, the step of thermally oxidizing said trench including a step of heating said silicon carbide substrate at not less than 1300° C.;
• and
• forming a gate electrode on said trench with said gate insulating film being interposed therebetween, wherein
• in said step of forming said corner insulating film, said first side surface and said second side surface are exposed from said corner insulating film, and
• the step of thermally oxidizing said trench includes steps of:
• increasing a temperature of said silicon carbide substrate from a temperature of less than 1300° C. to a temperature of not less than 1300° C. in a non-oxidizing atmosphere;
• and
• changing an atmosphere surrounding said silicon carbide substrate from the non-oxidizing atmosphere to an oxidizing atmosphere while maintaining the temperature of said silicon carbide substrate at not less than 1300° C.