Patent ID: 7419893

Claim:
A method for fabricating semiconductor device having a plurality of well structures including a triple-well structure, comprising the steps of: forming a thermally stable film on a first conductivity type substrate; forming a first resist film having an opening at a position corresponding to a first well forming area on the thermally stable film; removing the thermally stable film selectively by masking with the first resist film so as to make a neutering mask; implanting second conductivity type impurity into the first well forming area by masking with the neutering mask and the first resist film; removing the first resist film; forming a first well having a second conductivity type by diffusing and activating the second conductivity type impurity implanted into the first well forming area with a heating process; implanting first conductivity type impurity into a surface region of the first well forming area by masking with the neutering mask to neutralize the second conductivity type impurity implanted; removing the neutering mask; forming a second resist film having openings at a position corresponding to the second well forming area in the neutralized area and at a position corresponding to a third well forming area which is located in an area other than the first well forming area on the substrate; implanting additional impurity of the first conductivity type into the second and the third well forming area by masking with the second resist film; removing the second resist film; and forming a second well at the second well forming area and a third well at the third well forming area by diffusing and activating the additional impurity of the first conductivity type implanted into the second and the third well forming areas with a heating process.