Method for forming integrated circuit regions defined by recessed dielectric isolation

Claim 1

In the fabrication of integrated circuits, a method for forming dielectrically isolated regions in a silicon substrate comprising introducing conductivity-determining impurities into the substrate to form at least one region of one-type conductivity at the surface of said substrate forming over at least a part of said surface of said region, a composite mask comprising a lower layer of silicon dioxide in contact with said surface, and an upper layer of silicon nitride on said lower layer, said mask having a plurality of apertures extending therethrough, etching recesses in the portions of said substrate exposed in said apertures, thermally oxidizing the recessed portions of said substrate to an extent sufficient to form regions of recessed silicon dioxide abutting and laterally defining said at least one region of one-type conductivity, said mask acting as a barrier to prevent oxidation of the unrecessed surface of said substrate, providing a layer of electrically insulative material over at least a portion of the surface of said substrate by a processing step comprising at least the removal of said silicon nitride layer, forming at least one contact opening through said electrically insulative layer to expose at least a portion of said at least one region of one-type conductivity, said contact opening exposing a portion of a region of recessed silicon dioxide abutting said one-type conductivity region and depositing metal in said contact opening to form a contact to said region of one-type conductivity, said contact over-lapping said recessed silicon dioxide.