Method for forming dielectric isolation in integrated circuits

Claim 1

In the fabrication of integrated circuits, a method for forming dielectrically isolated regions in a silicon substrate comprising forming over a silicon substrate surface of one-type conductivity a first mask comprising silicon nitride having a plurality of openings therethrough, etching to recess the silicon substrate exposed in said plurality of openings, thermally oxidizing the recessed portions of the silicon substrate to form regions of recessed silicon dioxide extending into the substrate, removing said mask to expose the silicon substrate, carrying out a blanket introduction of impurities of opposite-type conductivity into the portions of the substrate surface remaining unoxidized to form regions which do not extend from the surface of said substrate to a substrate depth beyond that of the regions of recessed silicon dioxide, epitaxially depositing a layer of silicon of said opposite-type conductivity on said substrate surface, forming over said epitaxial layer a second mask comprising silicon nitride having a plurality of openings therethrough, in registration with said plurality of openings in said first mask, etching to recess the silicon epitaxial layer exposed in said plurality of openings in said second mask, and thermally oxidizing the recessed portions of said epitaxial layer to an extent sufficient to form regions of recessed silicon dioxide extending through said epitaxial layer into registered contact respectively with said regions of recessed silicon dioxide formed in the substrate.