Insulated gate semiconductor device and its manufacturing method

Abstract

A gate electrode includes a first polysilicon film remaining on a first oxide film, a part of a second polysilicon layer superimposed on the polysilicon layer, and a part of the second polysilicon layer partially extending over second gate oxide films. Thus, the thickness of the gate electrode on the first gate oxide film is the same as that of the gate electrode of the prior art, but the film thickness t of the gate electrode on the second gate oxide films A and B is thinner than the thickness t of the prior art. Therefore, the height gap h between the gate electrode and the N + type source layer and the height gap h between the gate electrode and the N + type drain layer become smaller compared to those of prior art, leading to the improved flatness of the interlayer oxide film