Dry oxidation mechanisms of thin dielectric films formed under n/sub 2/o using isotopic tracing methods

Abstract

We investigated the mechanisms of thermal reoxidation in dry O2 of silicon oxynitride films prepared by processing Si~100! wafers in a rapid thermal furnace in a pure nitrous oxide ~N2O! ambient, using isotopic tracing of oxygen and nitrogen. Standard nuclear reaction analyses for the measurement of the total amounts of the different isotopes, and very narrow resonant nuclear reactions for high resolution ~1 nm! depth profiling of these elements were used. The silicon oxynitride films grown in pure 15N2 16O were 8-nm thick, with a small amount of nitrogen localized near the interfacial region. Under reoxidation in dry 18O2 , the thickness of the dielectric film increased while a pronounced isotopic exchange took place between the 18O from the gas and the 16O from the film, as well as a significant loss of 15N. This is in contrast with the reoxidation in dry O2 of pure SiO2 films, where the oxygen exchange is rather small as compared to that observed in the present case.