Semiconductor device and method for manufacturing same

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

• forming a trench in a semiconductor wafer, the trench being provided on a front surface side of the semiconductor wafer, the semiconductor wafer including a portion to be a first semiconductor layer of a first conductivity type;
• forming a first insulating film over the semiconductor wafer, the first insulating film covering an inner surface of the trench;
• forming a second semiconductor layer of a second conductivity type on the portion to be the first semiconductor layer, the second semiconductor layer including second conductivity type impurities introduced in the semiconductor wafer on the front surface side;
• forming a third semiconductor layer of the first conductivity type on the second semiconductor layer, the third semiconductor layer including first conductivity type impurities introduced in the semiconductor wafer on the front surface side;
• forming a second insulating film on the first insulating film inside the trench, the second insulating film being formed so that a first space remains in the trench, the second insulating film having a dielectric constant smaller than a dielectric constant of the first insulating film;
• forming a field plate in the first space in the trench, the field plate facing the first semiconductor layer with the first and second insulating films interposed, the field plate being formed so that a second space remains on the field plate;
• forming a third insulating film on the field plate in the second space;
• removing a portion of the second insulating film and a portion of the third insulating film to form a third space in the trench;
• and
• forming a control electrode in the third space, the control electrode being electrically isolated from the field plate by the third insulating film, the control electrode facing the second semiconductor layer with the first insulating film interposed.