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 Si
3
N
4
and 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.