Silicon carbide semiconductor device and method of manufacturing silicon carbide semiconductor device

A silicon carbide semiconductor device, comprising:

• a silicon carbide semiconductor substrate of a first conductivity type, having a first main surface and a second main surface opposite to each other;
• a first semiconductor layer of the first conductivity type, provided on the first main surface of the silicon carbide semiconductor substrate, and having an impurity concentration lower than an impurity concentration of the silicon carbide semiconductor substrate, the first semiconductor layer having a first surface and a second surface opposite to each other, the second surface facing the silicon carbide semiconductor substrate;
• a second semiconductor layer of a second conductivity type, provided on the first surface of the first semiconductor layer, the second semiconductor layer having a first surface and a second surface opposite to each other, the second surface of the second semiconductor layer facing the silicon carbide semiconductor substrate;
• a first semiconductor region of the first conductivity type, selectively provided in the second semiconductor layer at the first surface of the second semiconductor layer;
• a trench penetrating through the first semiconductor region and the second semiconductor layer, and reaching the first semiconductor layer;
• a gate insulating film provided in the trench;
• a gate electrode provided on the gate insulating film in the trench;
• an interlayer insulating film provided on the gate electrode;
• a first electrode provided on the second semiconductor layer and the first semiconductor region;
• and
• a second electrode provided on the second main surface of the silicon carbide semiconductor substrate, wherein
• the gate insulating film is configured by a first gate insulating film provided on a surface of a semiconductor body layer, a second gate insulating film provided on a first surface of the first gate insulating film opposite to a second surface of the first gate insulating film facing the semiconductor layer, and a third gate insulating film provided on a first surface of the second gate insulating film opposite to a second surface of the second gate insulating film facing the semiconductor layer, the semiconductor body layer being configured by the first semiconductor region, the second semiconductor layer, and the first semiconductor layer,
• the first gate insulating film is a silicon nitride layer,
• the second gate insulating film is a silicon oxide film, and
• the third gate insulating film is a silicon oxide film having a nitrogen area density lower than a nitrogen area density of the second gate insulating film.