Selective oxidation technologies for high density MOS

Selective oxidation technologies using various thicknesses of silicon nitride formed by low-pressure chemical vapor deposition (LPCVD), plasma assisted nitridation in ammonia, and by nitrogen ion implantation were investigated. The transition region ("bird\´s beak") profiles were found to be related to the rigidity of the nitride film and also the oxidation underneath the nitride film via the buffer oxide or even a native oxide. With complete elimination of any oxide between Si3N4and Si achieved by implanting with nitrogen ions or nitriding in an ammonia plasma, a very abrupt transition region was achieved. This new sealed interface localized oxidation (SILO) technology appears to have low crystal defect density suitable for VLSI MOS technology.