Semiconductor device
A semiconductor device includes a semiconductor layer made of a wide bandgap semiconductor and including a gate trench; a gate insulating film formed on the gate trench; and a gate electrode embedded in the gate trench to be opposed to the semiconductor layer through the gate insulating film. The semiconductor layer includes a first conductivity type source region; a second conductivity type body region; a first conductivity type drift region; a second conductivity type first breakdown voltage holding region; a source trench passing through the first conductivity type source region and the second conductivity type body region from the front surface and reaching a drain region; and a second conductivity type second breakdown voltage region selectively formed on an edge portion of the source trench where the sidewall and the bottom wall thereof intersect with each other in a parallel region of the source trench.
1. A semiconductor device comprising:
a semiconductor layer made of a wide bandgap semiconductor having a gate trench provided with a sidewall and a bottom wall;
a gate insulating film formed on the sidewall and the bottom wall of the gate trench; and
a gate electrode embedded in the gate trench to be opposed to the semiconductor layer through the gate insulating film, wherein
the semiconductor layer includes:
a source region of a first conductivity type formed to be exposed on the side of a front surface of the semiconductor layer for partially forming the sidewall of the gate trench;
a body region of a second conductivity type formed on a side of the source region closer to a rear surface of the semiconductor layer to be in contact with the source region for partially forming the sidewall of the gate trench;
a drift region of a first conductivity type formed on a side of the body region closer to the rear surface of the semiconductor layer to be in contact with the body region for forming the bottom wall of the gate trench; and
a first breakdown voltage holding region of a second conductivity type selectively formed on an edge portion of the gate trench where the sidewall and the bottom wall intersect with each other in a partial region of the gate trench, wherein
the semiconductor layer is partitioned by the gate trench to form a unit cell, the unit cell including the source region, the body region and the drift region, and having a corner portion,
the first breakdown voltage holding region is formed on a corner edge portion of the gate trench formed on the corner portion of the unit cell, such that the first breakdown voltage holding region reaches a portion of the body region immediately above the corner portion, and
the drift region includes:
a first region of a first impurity concentration forming the bottom wall of the gate trench; and
a second region of a second impurity concentration smaller than the first impurity concentration formed on a side of the first region closer to the rear surface of the semiconductor layer to be in contact with the first region.
2. The semiconductor device according to claim 1 , wherein
the impurity concentration in the first breakdown voltage holding region is higher than the impurity concentration in the drift region.
3. The semiconductor device according to claim 1 , wherein
the gate trench is formed in a latticed manner, and
the semiconductor layer includes a plurality of the unit cells provided in the form of polygonal prisms each having a plurality of the corner portions.
4. The semiconductor device according to claim 3 , wherein
the first breakdown voltage holding region is selectively formed on an intersection portion of the latticed gate trench.
5. The semiconductor device according to claim 3 , wherein
the semiconductor layer further includes a second conductivity type second breakdown voltage holding region, formed on a bottom wall of a linear portion of the latticed gate trench, having a width narrower than the width of the linear portion.
6. The semiconductor device according to claim 5 , wherein
the impurity concentration in the second breakdown voltage holding region is higher than the impurity concentration in the first breakdown voltage holding region.
7. The semiconductor device according to claim 5 , wherein
the thickness of the second breakdown voltage holding region is smaller than the thickness of the first breakdown voltage holding region.
8. The semiconductor device according to claim 1 , wherein the semiconductor layer further includes:
a source trench having a sidewall and a bottom wall, passing through the source region and the body region from the front surface and reaching the drift region; and
a second conductivity type second breakdown voltage holding region selectively formed on an edge portion of the source trench where the sidewall and the bottom wall intersect with each other in a partial region of the source trench.
9. The semiconductor device according to claim 1 , wherein
the thickness of the first region is greater than the thickness of the first breakdown voltage holding region.
10. The semiconductor device according to claim 1 , wherein
the thickness of the first region is not more than the thickness of the first breakdown voltage holding region.
11. The semiconductor device according to claim 1 , wherein
the interface between the first region and the second region undulates in response to a step caused by partial lowering of the front surface of the semiconductor layer resulting from the formation of the gate trench.
12. The semiconductor device according to claim 1 , wherein
the interface between the first region and the second region is at a constant distance from the front surface of the semiconductor layer.
13. The semiconductor device according to claim 1 , wherein
a portion of the gate insulating film on the bottom wall of the gate trench is thicker than a portion of the gate insulating film on the sidewall of the gate trench, and a top portion thereof is below the deepest portion of the body region.
14. The semiconductor device according to claim 1 , wherein
the front surface of the semiconductor layer is a C plane.
15. The semiconductor device according to claim 1 , wherein
the body region is formed by ion implantation.
16. The semiconductor device according to claim 1 , wherein the semiconductor layer is made of SiC.
17. A semiconductor device comprising:
a semiconductor layer made of a wide bandgap semiconductor having a gate trench provided with a sidewall and a bottom wall;
a gate insulating film formed on the sidewall and the bottom wall of the gate trench; and
a gate electrode embedded in the gate trench to be opposed to the semiconductor layer through the gate insulating film, wherein
the semiconductor layer includes:
a source region of a first conductivity type formed to be exposed on the side of a front surface of the semiconductor layer for partially forming the sidewall of the gate trench;
a body region of a second conductivity type formed on a side of the source region closer to a rear surface of the semiconductor layer to be in contact with the source region for partially forming the sidewall of the gate trench; and
a drift region of a first conductivity type formed on a side of the body region closer to the rear surface of the semiconductor layer to be in contact with the body region for forming the bottom wall of the gate trench, wherein
the drift region includes:
a first region of a first impurity concentration forming the bottom wall of the gate trench; and
a second region of a second impurity concentration smaller than the first impurity concentration formed on a side of the first region closer to the rear surface of the semiconductor layer to be in contact with the first region, and
the second region of the drift region has selectively a projection portion extending toward the side of the front surface of the semiconductor layer and sandwiched by the first region.
18. The semiconductor device according to claim 17 , wherein
the semiconductor layer further includes a first breakdown voltage holding region of a second conductivity type selectively formed on an edge portion of the gate trench where the sidewall and the bottom wall intersect with each other in a partial region of the gate trench.
19. The semiconductor device according to claim 17 , wherein the semiconductor layer is made of SiC.