Semiconductor device and method for manufacturing the same

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

• forming a trench in a semiconductor substrate adjacent to an upper surface of the semiconductor substrate;
• forming a gate insulating film and a gate electrode, the gate electrode being formed on the gate insulating film inside the trench to be insulated from the semiconductor substrate and to have an upper surface locating below the upper surface of the semiconductor substrate inside the trench;
• forming an interlayer insulating film extending above the upper surface of the semiconductor substrate and the upper surface of the gate electrode;
• etching the interlayer insulating film, the gate insulating film, and the semiconductor substrate using an etching gas so that the semiconductor substrate has a connection surface connecting between the upper surface of the semiconductor substrate and a side surface of the trench and locating below the upper surface of the semiconductor substrate, the gate insulating film has an upper surface locating below the connection surface, the interlayer insulating film has an upper surface locating below the upper surface of the gate insulating film, the connection surface of the semiconductor substrate, the upper surface of the gate insulating film, and the upper surface of the interlayer insulating film are each inclined to be displaced downward toward a center of the trench;
• and
• forming a metal film covering the upper surface of the semiconductor substrate, the connection surface of the semiconductor substrate, the upper surface of the gate insulating film, and the upper surface of the interlayer insulating film.