Manufacturing method of sidewall insulating film

Abstract

Disclosed are a semiconductor device having a sidewall insulating film free from the formation of fence-shaped residue when a conductive layer formed on the sidewall insulating film is anisotropically etched by means of plasma etching, and a method of forming the sidewall insulating film. The method of forming the sidewall insulating film includes the steps of isotropically etching an insulating film 4 formed on a polycrystalline silicon film 3 to be a gate electrode as much as a prescribed thickness, using resist as a mask, anisotropically etching the remaining part of insulating film 4 and polycrystalline silicon film 3, forming an insulating film 6 entirely over the surface, and forming a sidewall insulating film 6a on the side plane of polycrystalline silicon film 3. The resultant sidewall insulating film 6a has a cross-section reduced upwardly in width. A polycrystalline silicon film 7 formed on sidewall insulating film 6a will not have a surface in the vertical direction relative to a semiconductor substrate 1. Consequently, the disconnection of an upper layer interconnection can be effectively prevented, and miniaturization of elements can be achieved without forming fence-shaped residue, when polycrystalline silicon film 7 is anisotropically etched (plasma etching).