Method of manufacturing a ROM in a MOS-technology and memory fabricated with this method

摘要

On an n-silicon substrate a pattern of n-wells is formed by masking in first phase (a) and followed by p-well masking (b). Removal of the protective oxide layer enables enrichment- and depletion-mode transistors to be defined. After suppression of the mask of resin (R), the p-well definition is performed by implantation of p-type dopant (e.g. B) such that at the level of the initial n-type diffusion region, a p-doped region is achieved at the level of NMOS enrichment-mode transistors. In the depletion-mode transistor region the p-type implantation remains superficial and the underlying region is uncompensated.