Method for manufacturing silicon carbide semiconductor device having trench

1. 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.

2. The method for manufacturing the silicon carbide semiconductor device according to claim 1 , wherein

the step of thermally oxidizing said trench includes steps of:

changing the atmosphere surrounding said silicon carbide substrate from the oxidizing atmosphere to the non-oxidizing atmosphere while maintaining the temperature of said silicon carbide substrate at not less than 1300° C.; and

cooling said silicon carbide substrate from the temperature of not less than 1300° C. to a temperature of not more than 1000° C. while maintaining, as the non-oxidizing atmosphere, the atmosphere surrounding said silicon carbide substrate.

3. The method for manufacturing the silicon carbide semiconductor device according to claim 1 , wherein the step of changing the atmosphere surrounding said silicon carbide substrate from the non-oxidizing atmosphere to the oxidizing atmosphere includes a step of introducing oxygen gas into the atmosphere surrounding said silicon carbide substrate.

4. The method for manufacturing the silicon carbide semiconductor device according to claim 1 , wherein

the step of forming said corner insulating film includes steps of:

forming a covering insulating film to cover the region extending from said opening to said corner portion; and

patterning said covering insulating film.

5. The method for manufacturing the silicon carbide semiconductor device according to claim 4 , wherein

the step of forming said covering insulating film includes steps of:

forming a silicon film on said trench; and

thermally oxidizing said silicon film.

6. The method for manufacturing the silicon carbide semiconductor device according to claim 5 , wherein the step of forming said covering insulating film includes a step of forming a thermal oxidation film on said trench before the step of forming said silicon film.

7. The method for manufacturing the silicon carbide semiconductor device according to claim 6 , wherein the step of thermally oxidizing said silicon film is performed at less than 1300° C.

8. The method for manufacturing the silicon carbide semiconductor device according to claim 4 , wherein

the step of patterning said covering insulating film includes steps of:

forming a resist layer by applying a resist liquid to fill said trench with said covering insulating film being interposed therebetween;

patterning said resist layer by etching back said resist layer such that said resist layer partially remains on said trench; and

etching said covering insulating film using said resist layer as a mask after the step of patterning said resist layer.

9. The method for manufacturing the silicon carbide semiconductor device according to claim 8 , wherein the step of etching said covering insulating film is performed by wet etching.

10. 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 forming said corner insulating film includes steps of:

forming a covering insulating film to cover the region extending from said opening to said corner portion; and

patterning said covering insulating film.

11. The method for manufacturing the silicon carbide semiconductor device according to claim 10 , wherein

the step of forming said covering insulating film includes steps of:

forming a silicon film on said trench; and

thermally oxidizing said silicon film.

12. The method for manufacturing the silicon carbide semiconductor device according to claim 11 , wherein the step of forming said covering insulating film includes a step of forming a thermal oxidation film on said trench before the step of forming said silicon film.

13. The method for manufacturing the silicon carbide semiconductor device according to claim 12 , wherein the step of thermally oxidizing said silicon film is performed at less than 1300° C.

14. The method for manufacturing the silicon carbide semiconductor device according to claim 10 , wherein

the step of patterning said covering insulating film includes steps of:

forming a resist layer by applying a resist liquid to fill said trench with said covering insulating film being interposed therebetween;

patterning said resist layer by etching back said resist layer such that said resist layer partially remains on said trench; and

etching said covering insulating film using said resist layer as a mask after the step of patterning said resist layer.

15. The method for manufacturing the silicon carbide semiconductor device according to claim 14 , wherein the step of etching said covering insulating film is performed by wet etching.