Nitride cap sidewell oxide protection from BOE etch

Abstract

A new method of forming a self-aligned contact is achieved. A pattern of polysilicon gate electrode stack including a silicon oxide gate dielectric, a polysilicon gate electrode, a first thermal polyoxide layer over the top of said polysilicon gate electrode layer, a first silicon nitride layer over said first thermal polyoxide layer, and a TEOS layer over said silicon nitride layer is provided on a silicon substrate. Each of the layers has its side open to the ambient. Inert ions are implanted into the substrate which is not covered by the polysilicon gate electrode stack in such a manner as to reduce the possibility of the oxidation of the surface of the substrate. The pattern of polysilicon gate electrode stack and the surface of the said substrate are subjected to a thermal oxidizing ambient which causes oxidation of the sides open to the ambient of the polysilicon layer to form a second polyoxide layer on the sides of the polysilicon layer. A second silicon nitride layer is formed over the pattern of stack and the surface of the substrate. The second silicon nitride layer is anisotropically etched to remove the second silicon nitride from the top of the stack and from over the surface of the substrate while leaving the second silicon nitride layer remaining upon the sides of the stack to form a self-aligned opening to regions within the silicon substrate. A self-aligning contact to the regions is formed through said opening.

Dependencies are inferred from the claim text.