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

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

• preparing a silicon carbide semiconductor substrate of a first conductivity type, the silicon carbide semiconductor substrate having a first surface and a second surface opposite to each other;
• forming a first semiconductor layer of the first conductivity type on the first surface of the silicon carbide semiconductor substrate, the first semiconductor layer 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 of the first semiconductor layer facing the silicon carbide semiconductor substrate;
• forming a second semiconductor layer of the first conductivity type on the first surface of the first semiconductor layer, the second semiconductor layer having an impurity concentration in a range from 1.0×1018/cm3 to 5.0×1018/cm3, 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;
• forming a third semiconductor layer of the first conductivity type on the first surface of the second semiconductor layer, the third semiconductor layer having an impurity concentration lower than the impurity concentration of the silicon carbide semiconductor substrate, the third semiconductor layer having a first surface and a second surface opposite to each other, the second surface of the third semiconductor layer facing the silicon carbide semiconductor substrate;
• forming a fourth semiconductor layer of a second conductivity type, on the first surface of the third semiconductor layer, the fourth semiconductor layer having a first surface and a second surface opposite to each other, the second surface of the fourth semiconductor layer facing the silicon carbide semiconductor substrate;
• selectively forming a plurality of first semiconductor regions of the first conductivity type in the fourth semiconductor layer, at the first surface of the fourth semiconductor layer;
• forming a gate electrode via a gate insulating film in the fourth semiconductor layer, at least a portion of the gate electrode being positioned between the first semiconductor regions and the third semiconductor layer;
• irradiating protons, so that a concentration of the protons in the second semiconductor layer is in a range from 1.0×1013/cm3 to 1.0×1014/cm3;
• forming a first electrode on the front surface of the fourth semiconductor layer and surfaces of the first semiconductor regions;
• and
• forming a second electrode on the second surface of the silicon carbide semiconductor substrate.