Silicon carbide semiconductor device and method for manufacturing same
A trench has first to third side surfaces respectively constituted of first to third semiconductor layers. A first side wall portion included in a first insulating film has first to third regions respectively located on the first to third side surfaces. A second insulating film has a second side wall portion located on the first side wall portion. The second side wall portion has one end and the other end, the one end being connected to the second bottom portion of the second insulating film, the other end being located on one of the first and second regions, the other end being separated from the third region.
1. A silicon carbide semiconductor device comprising:
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, said silicon carbide substrate being provided with a trench, 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;
a gate insulating film provided on said trench, said gate insulating film having a first insulating film and a second insulating film, said first insulating film directly covering each of said side wall surface and said bottom surface, said second insulating film being provided on said first insulating film, said first insulating film having a first bottom portion and a first side wall portion, said first bottom portion being located on said bottom surface, said first side wall portion being located on said side wall surface, said first side wall portion having first to third regions respectively located on said first to third side surfaces, said second insulating film having a second bottom portion and a second side wall portion, said second bottom portion being located on said first bottom portion, said second side wall portion being located on said first side wall portion, said second side wall portion having one end and an other end, said one end being connected to said second bottom portion, the other end being located on one of said first and second regions, the other end being separated from said third region; and
a gate electrode provided on said trench with said gate insulating film being interposed therebetween.
2. The silicon carbide semiconductor device according to claim 1 , wherein the other end of said second side wall portion is located on a boundary between said first region and said second region.
3. The silicon carbide semiconductor device according to claim 1 , wherein the other end of said second side wall portion is separated from said second region and is located on said first region.
4. The silicon carbide semiconductor device according to claim 1 , wherein the other end of said second side wall portion is separated from said third region and is located on said second region.
5. The silicon carbide semiconductor device according to claim 4 , wherein said second semiconductor layer has a depth position in which an impurity concentration has a peak, and the other end of said second side wall portion is located deeper than said depth position.
6. The silicon carbide semiconductor device according to claim 1 , wherein the other end of said second side wall portion has an inclination angle of less than 70° relative to said first side wall portion.
7. The silicon carbide semiconductor device according to claim 1 , wherein said first and second insulating films respectively have first and second carbon atom concentrations, and said second carbon atom concentration is less than said first carbon atom concentration.
8. The silicon carbide semiconductor device according to claim 7 , wherein said first carbon atom concentration is more than 1×10 15 cm −3 and said second carbon atom concentration is less than 1×10 15 cm −3 .
9. The silicon carbide semiconductor device according to claim 1 , wherein said second insulating film is made of at least one of silicon oxide, silicon nitride and phosphosilicate glass.
10. The silicon carbide semiconductor device according to claim 1 , wherein said second insulating film is a thermal oxidation film of a film including silicon and including no carbon.