Patent ID: 7754568

Claim:
A method of fabricating a semiconductor device including a semiconductor substrate having a first and a second region, comprising: forming a first recess in the second region of the semiconductor substrate by a reactive ion etching (RIE) process; forming a first silicon oxide film in the recess; removing the first silicon oxide film so that an inner surface of the first recess and a first upper surface of the semiconductor substrate in the first and the second regions are exposed; forming a second silicon oxide film in the first recess so that a second upper surface of the second silicon oxide film protrudes from the first upper surface; forming a first polycrystalline silicon film on the second upper surface so that the first upper surface is exposed; forming a third silicon oxide film on the first upper surface so that a first height of a third upper surface of the third silicon oxide film is lower than a second height of the second upper surface; forming a second polycrystalline silicon film on the third upper surface except the second upper surface so that a fourth upper surface of the first polycrystalline silicon film is flush with a fifth upper surface of the second polycrystalline silicon film; forming an insulating film on the first and the second polycrystalline silicon film; forming a third polycrystalline silicon film on the insulating film; and etching the third polycrystalline silicon film, the insulating film and first polycrystalline silicon film in the second region to form a first gate electrode, and the third polycrystalline silicon film, the insulating film and second polycrystalline silicon film in the first region to form a second gate electrode.