Silicon carbide semiconductor device and method of manufacturing the same

A silicon carbide semiconductor device comprising:

• a silicon carbide substrate having a first main surface and a second main surface located opposite to the first main surface, the silicon carbide substrate including
• a first impurity region in contact with the first main surface and having a first conductivity type,
• a second impurity region located in the first impurity region, in contact with the first main surface, and having a second conductivity type different from the first conductivity type,
• a third impurity region having the second conductivity type and connected to a bottom of the second impurity region,
• an electric field relaxing region having the second conductivity type, located adjacent to the second impurity region, and having an impurity concentration lower than an impurity concentration in the third impurity region, and
• at least one guard ring region having the second conductivity type, located opposite to the second impurity region with the electric field relaxing region interposed therebetween, and having an impurity concentration lower than the impurity concentration in the third impurity region,
• the silicon carbide semiconductor device further comprising:
• an oxide film located on the first main surface of the silicon carbide substrate, and having an opening to expose the second impurity region;
• a first electrode electrically connected to the second impurity region through the opening;
• and
• a second electrode electrically connected to the second main surface of the silicon carbide substrate, wherein
• a depth of a bottom of the third impurity region from the first main surface is not less than 0.9 μm.

A method of manufacturing a silicon carbide semiconductor device, comprising:

• preparing a silicon carbide substrate having a first main surface and a second main surface located opposite to the first main surface, the silicon carbide substrate including a first impurity region in contact with the first main surface and having a first conductivity type;
• and
• forming, in the first impurity region, by ion implantation, a second impurity region, a third impurity region, an electric field relaxing region, and at least one guard ring region, each region having a second conductivity type different from the first conductivity type,
• the second impurity region being located in the first impurity region and in contact with the first main surface,
• the third impurity region being connected to a bottom of the second impurity region,
• the electric field relaxing region being located adjacent to the second impurity region, and having an impurity concentration lower than an impurity concentration in the third impurity region, and
• the at least one guard ring region being located opposite to the second impurity region with the electric field relaxing region interposed therebetween, and having an impurity concentration lower than the impurity concentration in the third impurity region,
• the method of manufacturing a silicon carbide semiconductor device further comprising:
• forming an oxide film on the first main surface of the silicon carbide substrate by thermal oxidation of the silicon carbide substrate;
• forming an opening in the oxide film so as to expose the second impurity region;
• forming a first electrode electrically connected to the second impurity region through the opening;
• and
• forming a second electrode electrically connected to the second main surface of the silicon carbide substrate, wherein
• in the forming, with the first main surface as a depth reference position, the electric field relaxing region and the at least one guard ring region are formed to be shallower than the second impurity region.