Patent ID: 7196384

Claim:
A semiconductor device comprising: a first semiconductor domain and a second semiconductor domain isolated from each other by a field dielectric layer for device isolation formed selectively on a surface of a silicon semiconductor substrate; a first MOS device having a nitrogen-containing silicon oxide film formed on a surface of the first semiconductor domain as a gate dielectric; and a second MOS device having an oxygen-containing silicon nitride film formed on a surface of the second semiconductor domain as a gate dielectric, the oxygen-containing silicon nitride film having being formed from a silicon nitride film having an equivalent oxide thickness of 2.5 nm or less, wherein the oxygen concentration of the oxygen containing silicon nitride film is maximum near a surface of the oxygen-containing silicon nitride film, the oxygen concentration is minimum in an intermediate portion of the oxygen-containing silicon nitride film, and the oxygen concentration near a boundary between the oxygen-containing silicon nitride film and the silicon semiconductor substrate is lower than the oxygen concentration near the surface of the oxygen-containing silicon nitride film.