Patent ID: 7528041

Claim:
A method of manufacturing a semiconductor device, comprising: preparing a semiconductor substrate having first to fourth active regions and element isolating insulation films, the third and fourth active regions sandwiching the second active region, and the element isolating insulation films isolating the first to fourth active regions; forming a protective film for preventing the semiconductor substrate from being oxidized, the protective film having an opening over the second active region and the element isolating insulation film adjoining the second active region; forming a first gate insulation film on the second active region by conducting a thermal oxidation treatment through the opening; removing the protective film; forming a second gate insulation film on the first, third and fourth active regions, by conducting a thermal oxidation treatment, the second gate insulation film being thinner than the first gate insulation film; forming a first gate electrode on the second gate insulation film over a portion of the first active region, so that a remainder of the first active region is not covered with the first gate electrode; forming a second gate electrode on the first gate insulation film over the second active region, so that an entirety of the second active region is covered with the second gate electrode; forming a pair of first doped regions as a source and a drain in the first active region; and forming a pair of second doped regions as a source and a drain in the third and fourth active regions.