Method of forming a MOS field-effect transistor

Claim 1

A process for fabricating a MOS field-effect translator, comprising: a first step of preparing a semiconductor body comprising a substrate and an upper layer of a first conductivity type formed on said substrate and which forms an upper surface of said semiconductor body, and forming on the upper surface of said semiconductor body a multilayer film which comprises a gate insulating layer, a polycrystalline silicon layer formed on said gate insulating layer, and an upper insulating layer; a second step of removing a predetermined portion of said multilayer film, thereby exposing a predetermined area of said upper surface of said semiconductor body to form a window in said multilayer film; a third step of doping said semiconductor body through said window to form a base region of a second conductivity type opposite to said first conductivity type, extending into said upper layer of said semiconductor body from said upper surface, and a source region of the first conductivity type extending into said base region from said upper surface; a fourth step of performing thermal oxidation, thereby forming an oxide layer which extends into said source region from said upper surface, and which has a bottom surface entirely bounded by said base region and a side surface bounded by said source region, a side surface of said polycrystalline silicon layer formed within said window by said second step being oxidized during said thermal oxidation, and said polycrystalline being insulated and used as a gate electrode; a fifth step of removing said oxide layer formed in said upper surface and forming a depression in said upper surface of said semiconductor body; and a sixth step of forming in said depression a metal electrode contiguous to both of said base and source regions.