Patent ID: 6919252

Claim:
A method for manufacturing a MOS semiconductor device that includes the formation of elementary active elements in active zones of the device, said method comprising the steps of: masking and successive implantation and diffusion of dopant of a first conductivity type in a semiconductor substrate of a second conductivity type to form body regions of the elementary active elements; forming a field oxide layer on the substrate in inactive zones of the device; masking and selectively attacking the field oxide layer in the inactive zones so as to remove the field oxide layer only in at least two selected parts; implanting dopant of the first conductivity type in the semiconductor substrate of the second conductivity type in the inactive zones in order to form semiconductor regions of the first conductivity type under the at least two selected parts of the field oxide layer; thermally diffusing the dopant in the substrate in order to merge together the adjacent regions of the first conductivity type and to simultaneously form silicon oxide in the at least two selected parts in order, so as to obtain a silicon oxide layer having an alternation of at least two first zones and at least two second zones that are contiguous between to each other, with the first zones having a greater thickness than the second zones; and depositing a conductivity layer over the silicon oxide layer.