Silicon carbide semiconductor device

1. A silicon carbide semiconductor device, comprising:

a silicon carbide layer having a first main surface and a second main surface opposite to said first main surface,

said silicon carbide layer including

a first layer forming said first main surface and having a first conductivity type,

a second layer provided on said first layer and having a second conductivity type different from said first conductivity type, and

a third layer provided on said second layer to be spaced apart from said first layer, forming said second main surface, and having said first conductivity type,

said second main surface of said silicon carbide layer being provided with one or more trenches,

said one or more trenches having a sidewall surface passing through said third layer and said second layer to reach said first layer and a bottom portion located in said first layer,

said sidewall surface having a first sidewall surface and a second sidewall surface which are opposed to each other in a cross-sectional view,

said one or more trenches further having, in a cross-sectional view, a first corner portion which is an intersection between said first sidewall surface and said bottom portion and a second corner portion which is an intersection between said second sidewall surface and said bottom portion,

said first layer having one or more second-conductivity-type regions located on a side of said first main surface relative to said bottom portion and having said second conductivity type,

in a cross-sectional view, said one or more second-conductivity-type regions being arranged to intersect with a line which passes through any of said first corner portion of said one or more trenches and said second corner portion of said one or more trenches and is in parallel to a <0001> direction of a silicon carbide crystal forming said silicon carbide layer, and

a ratio calculated by dividing SP by ST being not lower than 20% and not higher than 130%, where ST represents a total area of said one or more trenches in a boundary surface between said first layer and said second layer and SP represents a total area of said one or more second-conductivity-type regions in a plan view,

wherein said one or more second-conductivity-type regions being distant from said bottom portion, below said first corner portion, and below said second corner portion of one of said one or more trenches.

2. The silicon carbide semiconductor device according to claim 1 , wherein

a distance between said one or more second-conductivity-type regions and said bottom portion of said one or more trenches is not greater than 4 μm.

3. The silicon carbide semiconductor device according to claim 1 , wherein

a distance between said one or more second-conductivity-type regions and said first main surface is not smaller than 5 μm.

4. The silicon carbide semiconductor device according to claim 1 , further comprising a silicon carbide single-crystal substrate in contact with said first main surface.

5. The silicon carbide semiconductor device according to claim 4 , wherein

a dislocation density of a surface of said silicon carbide single-crystal substrate in contact with said first main surface is not less than 50/cm′ and not more than 5000/cm 2 .

6. The silicon carbide semiconductor device according to claim 4 , wherein

a surface of said silicon carbide single-crystal substrate in contact with said first main surface has an off angle not smaller than 2° and not greater than 8° with respect to a {000-1} plane.

7. The silicon carbide semiconductor device according to claim 1 , wherein

on said sidewall surface of said one or more trenches, said second layer is provided with a surface having a first surface having a plane orientation {0-33-8}.

8. The silicon carbide semiconductor device according to claim 7 , wherein

said surface microscopically includes said first surface and said surface microscopically further includes a second surface having a plane orientation {0-11-1}.

9. The silicon carbide semiconductor device according to claim 8 , wherein

said first and second surfaces of said surface form a combined surface having a plane orientation {0-11-2}.

10. The silicon carbide semiconductor device according to claim 9 , wherein

said surface has an off angle of 62°±10° macroscopically with respect to a {000-1} plane.