Sloped silicon nitride etch for smoother field oxide edge

Abstract

A method of fabricating an integrated circuit on a silicon substrate in such a manner as to avoid the requirement of over-etching the polysilicon usually necessary to prevent shorting of adjacent devices by poly filaments caused by deep polysilicon pockets in notch areas created in the field oxide during its growth. The notches are prevented by forming the nitride mask with sloped rather than perpendicular side walls. The sloped side walls present less resistance to the growing oxide than does the usual perpendicular wall and thus does not dig into the growing oxide to form the notches. The edge of the resultant field oxide is therefore smoother, permitting easier and more complete removal of the polysilicon without the need for over-etching.