Semiconductor device and method for manufacturing semiconductor device

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

• a step of forming a first trench and a second trench by selectively removing, through a mask, a semiconductor layer of a first conductivity type which has a first surface and a second surface on an opposite side to the first surface and in which a second semiconductor layer of a second conductivity type is embedded, with the first trench and the second trench extending from the first surface in a thickness direction of the semiconductor layer and penetrating the second semiconductor layer in a sectional view in a direction intersecting the first surface;
• a step of implanting an impurity of the second conductivity type into side surfaces of the first trench and the second trench while the mask is left on the semiconductor layer;
• a step of forming a first insulating film on at least a side surface of the first trench;
• a step of forming a second insulating film on at least a side surface of the second trench;
• a step of forming a first sinker layer of the second conductivity type and a second sinker layer of the second conductivity type by heat diffusion of an impurity of the second conductivity type such that the first sinker layer extends in a depth direction of the first trench and is in contact with the second semiconductor layer and the first insulating film, and the second sinker layer extends in a depth direction of the second trench and is in contact with the second semiconductor layer and the second insulating film;
• a step of forming a diode impurity region of the first conductivity type on the first surface of the semiconductor layer so as to be in contact with the first sinker layer;
• a step of forming a first wiring so as to be electrically connected to the diode impurity region;
• and
• a step of forming a second wiring so as to be electrically connected to the second sinker layer.