The structure and electronic properties of silicon oxynitride gate dielectrics

Despite considerable progress achieved over the past few years in understan ding ultrathin oxynitrides, several fundamental questions, in particular, t he oxynitridation mechanism and the mechanisms behind the beneficial role o f nitrogen are still not well understood. To improve understanding of the e xplanations which have been proposed for the phenomena specific to silicon oxynitride and for the nature of the defects, a study of the electron struc ture of a MOS system using silicon oxynitrides as the gate oxide and based on a molecular dynamics geometry optimization method, was carried out. Inve stigations of the band energy parameters versus the SiON film thickness and oxygen to nitrogen ratio were done theoretically as well as experimentally . Theoretical calculations were done by norm-conserving non-local pseudopot entials together with molecular dynamics geometry optimization. Experimenta l investigations included spectroscopic investigations of the film absorpti on. Both theoretical and experimental data indicate that the effective band energy gap possess modulated-like dependence versus the film thickness and oxygen/nitrogen ratio. The origin of the observed phenomenon is caused by specific electron-phonon anharmonic interactions between the film and the S i substrate.