Semiconductor device and method of manufacturing semiconductor device

A method of manufacturing a semiconductor device, the method comprising steps of:

• preparing a semiconductor substrate of a first conductivity type;
• forming a base layer of a second conductivity type in a surface portion of the semiconductor substrate;
• forming a trench that reaches below the base layer in the semiconductor substrate;
• forming a first insulating film on an upper surface of the semiconductor substrate including an inner surface of the trench;
• embedding a first conductive film in the trench by forming the first conductive film on the first insulating film;
• forming a first gate insulating film made of the first insulating film and a first gate electrode made of the first conductive film in a lower portion in the trench by removing the first insulating film and the first conductive film on the upper surface of the semiconductor substrate and in an upper portion in the trench;
• forming a second insulating film on the upper surface of the semiconductor substrate including the inner surface of the trench after forming the first gate insulating film and the first gate electrode;
• embedding a second conductive film in the trench by forming the second conductive film on the second insulating film;
• forming a second gate insulating film made of the second insulating film and a second gate electrode made of the second conductive film in the upper portion in the trench by removing the second insulating film and the second conductive film on the upper surface of the semiconductor substrate;
• forming a source layer of the first conductivity type in a surface portion of the base layer;
• forming an interlayer insulating film including an oxide film so as to cover the second gate insulating film and the second gate electrode;
• and
• performing annealing in an oxygen atmosphere on the interlayer insulating film.