Semiconductor device and method for manufacturing semiconductor device

A semiconductor device comprising:

• a semiconductor substrate having an upper surface and a rear surface opposite to the upper surface, a trench being formed in the upper surface;
• a first main electrode provided on the upper surface of the semiconductor substrate;
• a second main electrode provided on the rear surface of the semiconductor substrate;
• a first gate electrode provided inside the trench;
• a first insulating film provided between the first gate electrode and a sidewall of the trench in a direction parallel to the upper surface of the semiconductor substrate;
• a second gate electrode provided on the first gate electrode inside the trench;
• a second insulating film provided between the second gate electrode and the sidewall of the trench in the direction parallel to the upper surface of the semiconductor substrate;
• and
• a third insulating film separating the first gate electrode and the second gate electrode in a direction from the upper surface to the rear surface of the semiconductor substrate, wherein
• the first insulating film includes an outer insulating film in contact with the semiconductor substrate, and an inner insulating film in contact with the first gate electrode, and
• a density of interface states of the inner insulating film is higher than a density of interface states of the outer insulating film.