The structure and electronic properties ofsilicon oxynitride gate dielectrics

Abstract

Despite considerable progress achieved over the pastfew years in understanding ultrathin oxynitrides, severalfundamental questions, in particular, the oxynitridationmechanism and the mechanisms behind the beneficial role ofnitrogen are still not well understood. To improve understandingof the explanations which have been proposed for the phenomenaspecific to silicon oxynitride and for the nature of thedefects, a study of the electron structure of a MOS systemusing silicon oxynitrides as the gate oxide and based on amolecular dynamics geometry optimization method, was carriedout. Investigations of the band energy parameters versus theSiON film thickness and oxygen to nitrogen ratio were done theoretically as well as experimentally. Theoretical calculationswere done by norm-conserving non-local pseudopotentials togetherwith molecular dynamics geometry optimization. Experimentalinvestigations included spectroscopic investigations of thefilm absorption. Both theoretical and experimental dataindicate that the effective band energy gap possessmodulated-like dependence versus the film thickness andoxygen/nitrogen ratio. The origin of the observed phenomenon iscaused by specific electron-phonon anharmonic interactionsbetween the film and the Si substrate.