Semiconductor device and method of manufacturing the same

A semiconductor device comprising a trench gate transistor which comprises:

• a trench provided in a semiconductor substrate;
• a gate electrode formed in the trench through a gate dielectric film;
• and
• a diffusion layer formed in the vicinity of the trench,
• wherein a cross-sectional contour of the trench is substantially U-shaped, a width of an opening portion of the trench is smaller than the width of a bottom portion of the trench, and a surface extending from the opening portion to the bottom portion has a curved surface.

A method of manufacturing a semiconductor device having a trench gate transistor, comprising:

• forming a trench in a semiconductor substrate;
• and
• forming a gate dielectric film and a gate electrode in the trench,
• wherein the step of forming the trench in the semiconductor substrate comprises:
• forming a first recess portion in the semiconductor substrate;
• after forming an oxide film on an inner surface of the first recess portion, removing the oxide film located at a bottom surface of the first recess portion;
• forming a second recess portion connected to the first recess portion by etching the bottom surface of the first recess portion using the oxide film remaining on a side surface of the first recess portion as a mask;
• performing hydrogen anneal to make a cross-sectional contour of the second recess portion a substantially circular arc shape;
• performing sacrifice oxidation;
• and
• removing the oxide film.