Patent ID: 7687385

Claim:
A method of manufacturing a semiconductor device exhibiting a high breakdown voltage, the method comprising the steps of: forming an oxide film on a semiconductor substrate; forming a nitride film on the oxide film; coating a photoresist on the nitride film; positioning a photomask on the photoresist; selectively forming an opening in the photoresist through the photomask; removing the portion of the nitride film beneath the opening of the photoresist and that portion of the nitride film within a predetermined lateral range from the edge of the opening of the photoresist, using the photoresist as a mask; implanting impurity ions of a first conductivity type into the semiconductor substrate using the photoresist as a mask; removing the photoresist; thermally treating the portion of the oxide film not covered by the nitride film, thereby forming a selectively oxidized film; removing the nitride film; implanting impurity ions of a second conductivity type into the semiconductor substrate using the selectively oxidized film as a mask; and thermally driving the implanted impurity ions of the first conductivity type and the implanted impurity ions of the second conductivity type, thereby forming an impurity diffusion region of the first conductivity type and an impurity diffusion region of the second conductivity type in the semiconductor substrate.