Semiconductor field oxide formation process using a sealing sidewall of consumable nitride

Claim 1

A process for forming field oxide regions between active regions in a semiconductor substrate, comprising the steps of: forming over the substrate active regions a pad oxide layer; forming over the pad oxide layer a first silicon nitride layer to a thickness in the range of 100 nm or greater; anisotropically etching in the presence of a photoresist mask through the first nitride layer, the pad oxide layer, and into the substrate to define field oxide regions with substantially vertical sidewalls; forming a conformal second silicon nitride layer, over the patterned structure of the substrate and layers including the substantially vertical sidewalls, to a nominal thickness of 10-13 nm; anisotropically etching the horizontally disposed surfaces of the second silicon nitride layer to expose selected horizontally disposed surfaces of the substrate, while retaining second silicon nitride on the substantially vertical sidewalls of a thickness so that it will be consumed and converted to silicon dioxide when the substrate is oxidized to lift said retained sidewall silicon nitride; oxidizing the exposed substrate and second silicon nitride in a proportion to effectuate concurrent oxidation and lifting and bending, beginning at the low edge of the retained sidewall silicon nitride; continuing the oxidation of the substrate and the lifting of the sidewall silicon nitride until the upper surface of the oxidized substrate approximates the level of the pad oxide layer by the sidewall silicon nitride being consumed and converted in to silicon dioxide; and removing the remaining silicon nitride.