Process of forming recessed dielectric regions in a monocrystalline silicon substrate

A method of forming a recessed dielectric region in a silicon substrate comprising:

• forming an SiO.sub.2 layer on the surface of said silicon substrate,
• forming a relatively thick layer of polycrystalline silicon over said SiO.sub.2 layer.
• depositing a resist layer over said polycrystalline silicon layer,
• exposing and developing said resist layer to form openings that define the desired locations of desired said recessed dielectric regions,
• forming openings through said exposed polycrystalline silicon layer, said SiO.sub.2 layer, and into said substrate to the desired depth that defines isolation trenches,
• chemical vapor depositing a layer of dielectric material over the surface of said substrate to a depth sufficient to fill said trenches,
• depositing a planarizing layer over said layer of dielectric material,
• reactive ion etching said planarizing layer, said layer of dielectric material, said second layer and partially into said polycrystalline silicon layer,
• selectively removing the remaining polycrystalline silicon layer with an agent that etches silicon at a significantly higher rate than SiO.sub.2 to expose said SiO.sub.2 layer as the surface layer.