Semiconductor device with gradual injection of charge carriers for softer reverse recovery
A semiconductor device a first semiconductor layer of a first conductivity type at a first main side of a semiconductor wafer and a second semiconductor layer of a second conductivity type at second main side. The second semiconductor layer forms a pn junction with the first semiconductor layer. A first electrode is in ohmic contact with the first semiconductor layer and a second electrode layer is in ohmic contact with the second semiconductor layer. A first semiconductor region of the first conductivity type completely embedded in the second semiconductor layer and a second semiconductor region of the first conductivity type completely embedded in the second semiconductor layer.
1. A semiconductor device comprising:
a first semiconductor layer of a first conductivity type at a first main side of a semiconductor wafer;
a first electrode layer at the first main side and in ohmic contact with the first semiconductor layer;
a second semiconductor layer of a second conductivity type, the second semiconductor layer forming a first pn junction with the first semiconductor layer;
a third semiconductor layer of the second conductivity type at a second main side of the semiconductor wafer, the third semiconductor layer having a maximal doping concentration that is at least one order of magnitude higher than a maximal doping concentration of the second semiconductor layer;
a second electrode layer at the second main side and in ohmic contact with the third semiconductor layer;
a fourth semiconductor layer of the second conductivity type between the second semiconductor layer and the third semiconductor layer, the fourth semiconductor layer having a maximal doping concentration that is lower than the maximal doping concentration of the third semiconductor layer and that is higher than the maximal doping concentration of the second semiconductor layer;
a first semiconductor region of the first conductivity type completely embedded in the fourth semiconductor layer; and
a second semiconductor region of the first conductivity type completely embedded in the fourth semiconductor layer, wherein during reverse recovery, a first conductivity type charge carrier injection duration of the first semiconductor region is different from a first conductivity type charge carrier injection duration of the second semiconductor region.
2. The semiconductor device according to claim 1 , wherein a distance from the first semiconductor region to the second main side is different than a distance of the second semiconductor region to the second main side.
3. The semiconductor device according to claim 1 , wherein a distance of the first semiconductor region to the first main side is different from a distance of the second semiconductor region to the first main side.
4. The semiconductor device according to claim 1 , wherein the first semiconductor region overlaps with the second semiconductor region in an orthogonal projection onto a plane parallel to the second main side.
5. The semiconductor device according to claim 1 , wherein a maximal doping concentration of the first semiconductor region is different than a maximal doping concentration of the second semiconductor region.
6. The semiconductor device according to claim 1 , wherein the first semiconductor region and the second semiconductor region do not overlap with each other in each orthogonal projection onto a plane perpendicular to the second main side.
7. The semiconductor device according to claim 1 , wherein the first semiconductor region and the second semiconductor region are separated from each other.
8. The semiconductor device according to claim 1 , wherein the first semiconductor region and the second semiconductor region are closer to the second main side than to the first pn junction.
9. The semiconductor device according to claim 1 , wherein a thickness of the first semiconductor region is substantially the same as a thickness of the second semiconductor region when thickness is measured in a direction from the first main side to the second main side.
10. The semiconductor device according to claim 1 , wherein a thickness of the first semiconductor region is different than a thickness of the second semiconductor region when thickness is measured in a direction from the first main side to the second main side.
11. A semiconductor device comprising:
a first semiconductor layer of a first conductivity type at a first main side of a semiconductor wafer;
a first electrode layer at the first main side and in ohmic contact with the first semiconductor layer;
a second semiconductor layer of a second conductivity type, the second semiconductor layer forming a pn junction with the first semiconductor layer;
a third semiconductor layer of the second conductivity type at a second main side of the semiconductor wafer, the third semiconductor layer having a maximal doping concentration that is at least one order of magnitude higher than a maximal doping concentration of the second semiconductor layer;
a second electrode layer at the second main side and in ohmic contact with the third semiconductor layer;
a fourth semiconductor layer of the second conductivity type between the second semiconductor layer and the third semiconductor layer, the fourth semiconductor layer having a maximal doping concentration that is lower than the maximal doping concentration of the third semiconductor layer and that is higher than the maximal doping concentration of the second semiconductor layer;
a first semiconductor region of the first conductivity type completely embedded in the fourth semiconductor layer, the first semiconductor region spaced from the first main side by a first distance and spaced from the second main side by a second distance; and
a second semiconductor region of the first conductivity type completely embedded in the fourth semiconductor layer and separated from the first semiconductor region, the second semiconductor region spaced from the first main side by a third distance that is different than the first distance and spaced from the second main side by a fourth distance that is different than the second distance, wherein a maximal doping concentration of the second semiconductor region is less than or equal to a maximal doping concentration of the first semiconductor region.
12. The semiconductor device according to claim 11 , wherein the first semiconductor region overlaps with the second semiconductor region in an orthogonal projection onto a plane parallel to the second main side.
13. The semiconductor device according to claim 11 , wherein the first semiconductor region and the second semiconductor region do not overlap with each other in each orthogonal projection onto a plane perpendicular to the second main side.
14. A method for manufacturing a power semiconductor device, the method comprising:
providing a semiconductor wafer having a first main side and a second main side, the semiconductor wafer comprising:
a first semiconductor layer of a first conductivity type at the first main side;
a second semiconductor layer of a second conductivity type, the second semiconductor layer forming a pn junction with the first semiconductor layer;
a third semiconductor layer of the second conductivity type at the second main side, the third semiconductor layer having a maximal doping concentration that is at least one order of magnitude higher than a maximal doping concentration of the second semiconductor layer;
a fourth semiconductor layer of the second conductivity type between the second semiconductor layer and the third semiconductor layer, the fourth semiconductor layer having a maximal doping concentration that is lower than the maximal doping concentration of the third semiconductor layer and that is higher than the maximal doping concentration of the second semiconductor layer;
a first semiconductor region of the first conductivity type completely embedded in the fourth semiconductor layer; and
a second semiconductor region of the first conductivity type completely embedded in the fourth semiconductor layer and spaced from the first semiconductor region, wherein during reverse recovery, a first conductivity type charge carrier injection duration of the first semiconductor region is different from a first conductivity type charge carrier injection duration of the second semiconductor region;
forming a first electrode layer at the first main side and in ohmic contact with the first semiconductor layer; and
forming a second electrode layer at the second main side and in ohmic contact with the third semiconductor layer.
15. The method of claim 14 , further comprising forming the semiconductor wafer, wherein forming the semiconductor wafer comprises:
providing a semiconductor substrate of the second conductivity type, the semiconductor substrate having a third main side and a fourth main side opposite to the third main side;
applying first dopants of the first conductivity type at the fourth main side for forming the first semiconductor region;
thereafter, forming a fifth semiconductor layer of the second conductivity type on the fourth main side, the fifth semiconductor layer having a fifth main side coinciding with the fourth main side and a sixth main side opposite to the fifth main side;
thereafter, applying second dopants of the first conductivity type at the sixth main side for forming the second semiconductor region;
thereafter, forming a sixth semiconductor layer of the second conductivity type on the sixth main side, the sixth semiconductor layer having a seventh main side coinciding with the sixth main side and an eighth main side opposite to the seventh main side; and
annealing the substrate to activate the applied first dopants and the applied second dopants thereby forming the first semiconductor region and the second semiconductor region.
16. The method according to claim 15 , wherein the fifth semiconductor layer and the sixth semiconductor layer are formed by epitaxy.
17. The method according to claim 15 , wherein the fifth semiconductor layer and the sixth semiconductor layer are formed at a temperature below 450° C.
18. The method according to claim 17 , wherein annealing the substrate comprises:
performing a first annealing step to activate the applied first dopants before the step of forming the fifth semiconductor layer; and
performing a second annealing step to activate the applied second dopants before the step of forming the sixth semiconductor layer and after the first annealing step.
19. The method according to claim 14 , wherein a distance from the first semiconductor region to the second main side is different than a distance of the second semiconductor region to the second main side; and
a distance of the first semiconductor region to the first main side is different from a distance of the second semiconductor region to the first main side.
20. The method according to claim 14 , wherein a maximal doping concentration of the first semiconductor region is different than a maximal doping concentration of the second semiconductor region.