Selective polysilicon oxidation technology for defect free isolation

A new isolation technology is described for small geometry MOS LSI´s in which selective polysilicon oxidation is utilized. In the process, a polysilicon film is deposited on a oxide layer grown on a silicon substrate, first. Thick thermal oxide is then selectively formed by polysilicon oxidation with a masking Si3N4film without pad oxide. The unoxidized polysilicon is etched off by a reactive ion etching, and then the residual polysilicon under the overhung oxide is oxidized for providing desired field oxide edge configuration. A test device was fabricated by this technology and the bird´s beak length was reduced to 0.15 µm, typically, in the case of no pad oxide. The feasibility of this technology for MOS VLSI´s was confirmed without any serious process induced defects.