The structure and electronic properties of silicon oxynitride gate dielectrics

Despite considerable progress achieved over the past few years in understanding ultrathin oxynitrides, several fundamental questions, in particular, the oxynitridation mechanism and the mechanisms behind the beneficial role of nitrogen are still not well understood. To improve understanding of the explanations which have been proposed for the phenomena specific to silicon oxynitride and for the nature of the defects, a study of the electron structure of a MOS system using silicon oxynitrides as the gate oxide and based on a molecular dynamics geometry optimization method, was carried out. Investigations 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 pseudopotentials together with molecular dynamics geometry optimization. Experimental investigations included spectroscopic investigations of the film absorption. 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 Si substrate.