Semiconductor device
Provided is a semiconductor device including a buffer region. Provided is a semiconductor device including: semiconductor substrate of a first conductivity type; a drift layer of the first conductivity type provided in the semiconductor substrate; and a buffer region of the first conductivity type provided in the drift layer, the buffer region having a plurality of peaks of a doping concentration, wherein the buffer region has: a first peak which has a predetermined doping concentration, and is provided the closest to a back surface of the semiconductor substrate among the plurality of peaks; and a high-concentration peak which has a higher doping concentration than the first peak, and is provided closer to an upper surface of the semiconductor substrate than the first peak is.
1. A semiconductor device comprising:
a semiconductor substrate of a first conductivity type;
a drift layer of the first conductivity type provided in the semiconductor substrate; and
a buffer region of the first conductivity type provided in the drift layer, the buffer region having a plurality of doping concentration peaks in a doping concentration distribution, wherein
the plurality of doping concentration peaks include four or more peaks,
a ratio NP i /NV i,i+1 is larger than a ratio NP i+1 /NP i , where NP i denotes a doping concentration of an i th peak, among the four or more peaks, from a back surface of the semiconductor substrate, NP i+1 denotes a doping concentration of an (i+1) th peak, among the four or more peaks, from the back surface of the semiconductor substrate, NP i+1 being higher than NP i , and NV i,i+1 denotes a doping concentration of a valley between the i th peak and the (i+1) th peak, for at least one value of i, where is a positive integer from 1 to the number of doping concentration peaks.
2. The semiconductor device according to claim 1 , wherein
the (i+1) th peak has the highest concentration among the plurality of doping concentration peaks.
3. The semiconductor device according to claim 1 , wherein
the (i+1) th peak is provided at a position between 1 μm and 12 μm inclusive from the back surface of the semiconductor substrate.
4. The semiconductor device according to claim 1 , wherein
the doping concentration NV i,i+1 of the valley between the i th peak and the (i+1) th peak is 10 times or more as high as a substrate concentration of the semiconductor substrate.
5. The semiconductor device according to claim 1 , wherein
the ratio NP i+1 /NP i satisfies 1<NP i+1 /NP i ≤100.
6. The semiconductor device according to claim 1 , wherein
the i th peak has the second highest concentration next to the (i+1) th peak among the plurality of doping concentration peaks.
7. The semiconductor device according to claim 1 , wherein
the semiconductor substrate has a doping concentration distribution in which a plurality of valleys are provided between the plurality of doping concentration peaks, and doping concentrations of the plurality of valleys sequentially decrease from a back surface side of the semiconductor substrate toward an upper surface side.
8. The semiconductor device according to claim 1 , further comprising a transistor section and a diode section.
9. The semiconductor device according to claim 8 , further comprising a collector region of a second conductivity type at a back surface of the transistor section.
10. The semiconductor device according to claim 1 , wherein
a doping concentration NP i+2 of an (i+2) th peak from the back surface of the semiconductor substrate among the four or more peaks is lower than the doping concentration NV i,i+1 of the valley between the i th peak and the (i+1) th peak.
11. The semiconductor device according to claim 1 , wherein
a distance X i+1 −X i in a depth direction between the (i+1) th peak and the i th peak is smaller than X i , where X i denotes a depth of the i th peak from the back surface of the semiconductor substrate and X i+1 denotes a depth of the (i+1) th peak from the back surface of the semiconductor substrate.
12. The semiconductor device according to claim 9 , wherein
a depth X 0 from the back surface of the semiconductor substrate to a boundary position between a first peak that is closest to the back surface of the semiconductor substrate and the collector region is smaller than a distance X 1 −X 0 in a depth direction, where X 1 denotes a depth of the first peak.
13. The semiconductor device according to claim 9 , wherein
a depth X 0 from the back surface of the semiconductor substrate to a boundary position between a first peak that is closest to the back surface of the semiconductor substrate and the collector region is larger than a distance X 1 −X 0 in a depth direction, where X 1 denotes a depth of the first peak.
14. The semiconductor device according to claim 1 , wherein
the four or more peaks includes a low-concentration peak that has a lower doping concentration than the doping concentration NP i+1 of the (i+1) th peak and that is provided closer to an upper surface of the semiconductor substrate than the (i+1) th peak.
15. The semiconductor device according to claim 9 , wherein
an integrated concentration from the collector region to the (i+1) th peak is higher than half of a critical integrated concentration of the semiconductor substrate.