Method of manufacturing silicon carbide semiconductor device

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

• forming a first epitaxial layer of a first conductivity type on a front surface of a silicon carbide substrate;
• epitaxially growing a second epitaxial layer of a second conductivity type on the first epitaxial layer;
• selectively forming a first semiconductor region of the second conductivity type by ion implantation in the second epitaxial layer, the first semiconductor region having an impurity concentration higher than that of the second epitaxial layer;
• selectively forming a second semiconductor region of the first conductivity type in the second epitaxial layer by ion implantation above the first semiconductor region, wherein a peak of impurity concentration in the second semiconductor region is higher than a peak of impurity concentration in the first semiconductor region;
• forming a trench to penetrate the second semiconductor region, the first semiconductor region, and the second epitaxial layer, and reach the first epitaxial layer;
• forming a gate insulating film in the trench;
• forming a gate electrode in the trench such that the gate electrode is surrounded in the trench by the gate insulating film;
• forming a first electrode contacting the second semiconductor region and the second epitaxial layer;
• and
• forming a second electrode on a rear surface of the silicon carbide substrate, wherein
• the first and second epitaxial layers have a second-conductivity-type impurity concentration profile,
• the first semiconductor region is formed to have a part of the second-conductivity-type impurity concentration profile in which concentration differences in a depth direction form a bell-shaped curve at the peak of impurity concentration higher than that of the second epitaxial layer,
• the impurity concentration of the second epitaxial layer is a range of 1×1016 atoms/cm3 to 2×1017 atoms/cm3,
• the impurity concentration of the peak of the second-conductivity-type impurity concentration profile is a range of 2×1016 atoms/cm3 to 5×1018 atoms/cm3, and
• the second-conductivity-type impurity concentration profile in the first and second epitaxial layers includes
• a first slope where the second-conductivity-type impurity concentration decreases from the peak toward an interface between the second epitaxial layer and the first epitaxial layer,
• a second slope where the second-conductivity-type impurity concentration decreases in the first epitaxial layer from the interface between the second epitaxial layer and the first epitaxial layer toward the second electrode, and
• an absolute value of the second slope is greater than an absolute value of the first slope.