Silicon carbide semiconductor device and method for manufacturing same

A silicon carbide semiconductor device comprising:

• a silicon carbide substrate having a first main surface and a second main surface opposite to the first main surface;
• a gate insulating film;
• and
• a source electrode, wherein
• the first main surface corresponds to a {0001} plane or a plane angled off by less than or equal to 8° relative to the {0001} plane,
• a gate trench and a source trench are provided in the first main surface,
• the gate trench is defined by a first side surface continuous to the first main surface and a first bottom surface continuous to the first side surface, and an angle of the first side surface relative to the first bottom surface is more than or equal to 50° and less than or equal to 65°,
• the source trench is defined by a second side surface continuous to the first main surface and a second bottom surface continuous to the second side surface, and an angle of the second side surface relative to the second bottom surface is more than or equal to 50° and less than or equal to 65°,
• the silicon carbide substrate includes
• a drift region having a first conductivity type,
• a body region provided on the drift region and having a second conductivity type different from the first conductivity type,
• a source region on the body region, the source region being separated from the drift region by the body region, the source region having the first conductivity type,
• a first region between the second bottom surface and the second main surface, the first region having the second conductivity type, and
• a second region in contact with the first region, the second region constituting at least a portion of the second side surface and the second bottom surface, the second region having the second conductivity type,
• the gate insulating film is in contact with the drift region, the body region, and the source region at the first side surface, and the gate insulating film is in contact with the drift region at the first bottom surface,
• the source electrode is in contact with the second region at the second side surface and the second bottom surface,
• the second region has a third region and a fourth region, the third region being in contact with the first region, the fourth region being continuous to the third region, the fourth region being in contact with the drift region, and
• a concentration of a second conductivity type impurity in the second bottom surface is higher than a concentration of the second conductivity type impurity in a boundary between the third region and the fourth region.

A method for manufacturing a silicon carbide semiconductor device, the method comprising:

• preparing a silicon carbide substrate having a first main surface and a second main surface opposite to the first main surface;
• and
• forming a gate trench and a source trench simultaneously in the first main surface by thermal etching, wherein
• the gate trench is defined by a first side surface continuous to the first main surface and a first bottom surface continuous to the first side surface,
• the source trench is defined by a second side surface continuous to the first main surface and a second bottom surface continuous to the second side surface,
• the silicon carbide substrate includes
• a drift region having a first conductivity type,
• a body region provided on the drift region and having a second conductivity type different from the first conductivity type,
• a source region on the body region, the source region being separated from the drift region by the body region, the source region having the first conductivity type, and
• a first region between the second bottom surface and the second main surface, the first region having the second conductivity type,
• the method further comprising:
• forming a second region by performing ion implantation to the second side surface and the second bottom surface, the second region being in contact with the first region, the second region constituting at least a portion of the second side surface and the second bottom surface, the second region having the second conductivity type;
• performing activation annealing to the silicon carbide substrate after the forming of the second region;
• forming a gate insulating film after the performing of the activation annealing to the silicon carbide substrate, the gate insulating film being in contact with the drift region, the body region, and the source region at the first side surface, the gate insulating film being in contact with the drift region at the first bottom surface;
• and
• forming a source electrode in contact with the second region at the second side surface and the second bottom surface, wherein
• the forming of the second region includes
• performing ion implantation on a condition of first energy and a first dose amount, and
• performing ion implantation on a condition of second energy and a second dose amount, the second energy being higher than the first energy, the second dose amount being lower than the first dose amount.