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 in which a first semiconductor layer of a first conductivity type is provided on a first surface of a starting substrate of the first conductivity type, the first surface of the starting substrate being opposite to a second surface of the starting substrate, the first semiconductor layer having an impurity concentration lower than an impurity concentration of the starting substrate;
• forming a plurality of first semiconductor regions of a second conductivity type in the first semiconductor layer by ion implantation;
• performing a first treatment of reversing warpage of the silicon carbide semiconductor substrate after forming the plurality of first semiconductor regions;
• forming a second semiconductor layer of the second conductivity type in the first semiconductor layer by ion implantation;
• forming a third semiconductor layer of the first conductivity type in a surface layer of the second semiconductor layer by ion implantation;
• activating the plurality of first semiconductor regions, the second semiconductor layer, and the third semiconductor layer;
• forming a plurality of trenches penetrating through the third semiconductor layer and the second semiconductor layer and reaching the first semiconductor layer, each of the plurality of trenches being formed at a position facing a corresponding one of the plurality of first semiconductor regions in a depth direction of the device;
• forming a plurality of gate electrodes in the plurality of trenches via a plurality of gate insulating films;
• forming a first electrode in contact with the third semiconductor layer and the second semiconductor layer;
• and
• forming a second electrode at the second surface of the starting substrate, wherein
• the first treatment of reversing the warpage includes forming, at a C-face of the silicon carbide semiconductor substrate, a first oxide film that is thicker than a second oxide film formed at a Si-face of the silicon carbide semiconductor substrate.