Semiconductor device

A semiconductor device comprising:

• a semiconductor substrate including an element region and a peripheral region located around the element region, the semiconductor substrate having a recess located at an upper surface of the semiconductor substrate in the peripheral region such that an upper surface of the semiconductor substrate in the element region protrudes further than the upper surface of the semiconductor substrate in the peripheral region;
• an upper electrode being in contact with the upper surface of the semiconductor substrate in the element region;
• a lower electrode being in contact with a lower surface of the semiconductor substrate in both of the element region and the peripheral region;
• an insulation layer covering a side surface and a bottom surface of the recess;
• and
• a field plate extending from the upper electrode to an upper portion of the peripheral region, the field plate being on a side of the insulation layer opposite to the side surface and the bottom surface of the recess with the insulation layer interposed between the field plate and each of the side surface and the bottom surface of the recess, wherein
• the semiconductor substrate includes:
• a high-concentration layer being an n-type layer and extending from the element region to the peripheral region, the high-concentration layer being in contact with the lower electrode, the high-concentration layer having a thick plate portion and a thin plate portion, an upper surface of the thick plate portion protruding further than an upper surface of the thin plate portion, the thick plate portion located in the element region, the thin plate portion extending from the element region to the peripheral region;
• a drift layer being an n-type layer and located in the element region, the drift layer being in contact with the upper surface of the thick plate portion in a stacking direction, the drift layer having a lower n-type impurity concentration than the high-concentration layer;
• and
• a low-concentration layer being an n-type layer and extending from the element region to the peripheral region, the low-concentration layer being in contact with a side surface of the drift layer, the low-concentration layer being in contact with the upper surface of the thin plate portion in the stacking direction, the low-concentration layer being in contact with a side surface of a stepped portion located at a boundary between the thick plate portion and the thin plate portion, the low-concentration layer being in contact with the insulation layer at the side surface and the bottom surface of the recess, the low-concentration layer having a lower n-type impurity concentration than the drift layer,
• the drift layer is connected to the upper electrode through at least one of a p-n junction or a Schottky barrier junction,
• a cross section of the semiconductor substrate perpendicularly intersects the stepped portion,
• the cross section of the semiconductor substrate includes a quadrilateral region surrounded by the side surface of the stepped portion, a first virtual line, the upper surface of the thin plate portion, and a second virtual line,
• the first virtual line is at a location shifted from the side surface of the stepped portion toward the peripheral region by a distance identical to a height of the stepped portion,
• the second virtual line is at a location shifted upward from the upper surface of the thin plate portion by a distance identical to the height of the stepped portion,
• a half or more of the quadrilateral region is not depleted in a case where an electric potential of the lower electrode with respect to the upper electrode is raised to a level causing an avalanche breakdown in the semiconductor substrate,
• the semiconductor substrate further includes a p-type anode layer, and
• a thickness of the low-concentration layer between the bottom surface of the recess and the thin plate portion is greater than one half of a thickness of the drift layer between the p-type anode layer and the thick plate portion, and is smaller than the thickness of the drift layer.