Abstract: In manufacturing an insulated gate field effect transistor integrated circuit using both a self-alignment diffusion process and a non-self-alignment diffusion process, a mask is formed having a combined pattern of areas at which a subsequent self-alignment diffusion and a non-self-alignment diffusion will occur. An oxidation prevention layer for preventing thermal oxidation of a substrate is selectively formed on a semiconductor substrate using the prepared mask. Those areas of the semiconductor substrate which are not covered by the oxidation prevention layer are oxidized by thermal oxidation to form oxidized layers thereon, and impurities are diffused first in the areas of the substrate corresponding to the non-self-alignment portion of the mask pattern and subsequently in the areas of the substrate corresponding to the self-alignment portions of the mask pattern to build in an insulated gate field effect transistor network.

Abstract: A method of making a MOS device, for instance, metal-oxide semiconductor type integrated circuit, is disclosed which comprises the following steps:Sequentially forming on a specified part of single crystal silicon substrate,Firstly, an oxide film,Secondly, a film to become a conductor film having a high-temperature-resistive nature, which does not melt at an impurity-diffusion temperature, serves as a diffusion mask and later serves as a gate electrode, for instance, polycrystalline silicon film; and thirdly, an oxidation-preventing film for preventing oxidation of said film to become the conductor film, wherein at least said conductor film and said overiding oxidation-preventing film have the same pattern so as to cover and prevent oxidation of said conductor film by said oxidation-preventing film, and thenDiffusing an impurity into the substrate from openings which are the parts other than those covered by said conductor film and said oxidation preventing film,The method being characterized by having a step