Process for creating fully-recessed field isolation regions by oxidizing a selectively-grown epitaxial silicon layer

A process for creating fully-recessed field isolation regions within the substrate of a substantially planar silicon wafer, said process comprising the following sequence of steps:

• a) creating a first pad oxide layer on the upper surface of the wafer;
• b) depositing a silicon nitride layer on top of the first pad oxide layer;
• c) creating a photoresist mask on the upper surface of the wafer which covers future active areas and exposes future field oxide regions;
• d) performing an anisotropic plasma etch which removes portions of the first pad oxide layer and first nitride layer in unmasked regions of the wafer, and also etches the substrate in said unmasked regions to create recessed substrate regions in the future field oxide regions, said recessed regions having substantially vertical sidewalls and substantially horizontal floors;
• e) removing the photoresist mask;
• f) creating a second pad oxide layer on exposed silicon within the recessed substrate regions;
• g) blanket depositing a second nitride layer;
• h) performing a second anisotropic etch which creates silicon nitride spacers on the substantially vertical sidewalls of said recessed regions, clears the floors of silicon nitride and silicon dioxide, and leaves said first nitride layer on top of the future active areas essentially intact;
• i) growing an epitaxial silicon layer within the recessed regions;
• j) thermally oxidizing the epitaxially-grown silicon layer to create field oxide plugs within the recessed regions;
• k) removing all remaining silicon nitride, thus creating substantially vertical voids around the peripheries of the field oxide plugs;
• and
• l) filling the voids with silicon dioxide.