Patent ID: 7164178

Claim:
A semiconductor device, comprising: a device isolation region for partitioning a principle surface of a semiconductor substrate into at least a first region and a second region; a first gate insulating film formed on the first region; a first gate electrode formed on the first gate insulating film; a second gate insulating film formed on the second region; and a second gate electrode formed on the second gate insulating film, wherein each of the first and second gate insulating films are with a single layer, a thickness of the second gate insulating film is smaller than a thickness of the first gate insulating film, a nitrogen concentration in the first gate insulating film is distributed only in a surface portion of the first gate insulating film such that nitrogen does not reach an interface between the first gate insulating film and the semiconductor substrate, and the nitrogen concentration in the second gate insulating film is distributed such that the nitrogen reaches an interface between the second gate insulating film and the semiconductor substrate.