Reduction of lateral phosphorus diffusion in CMOS n-wells

It is shown that it is possible to control lateral diffusion of phosphorus during an n-well drive-in through appropriate choices of surface thin-film and drive-in conditions. This permits reduced design rules with no change in lithography. The n-well drive-in process takes advantage of vacancy supersaturation caused by SiO formation. In an n-well structure, vacancies are injected only outside the well region, from the thin oxide, and virtually no vacancies are injected from the thick SiO₂-Si interface. Therefore, while normal P diffusion in the vertical direction in the well is still expected, lateral diffusion of P into the region under the thin oxide can be retarded