Growth study and theoretical investigation of the ultrathin oxide SiO2-Si heterojunction

The local atomic structure of ultrathin gate oxides and its effect and that of the corresponding SiO2-Si interface on the band offset of a MOS structure are investigated theoretically. To generate a physically realistic interface, we perform a "direct oxidation" simulation using quantum molecular dynamics. The critical thickness at which the oxidation rate switches from being limited by chemical kinetics to being diffusion limited is estimated. A novel method is introduced to evaluate the band offset within local orbital density functional theory. The valence band offset for the ultrathin oxide is found to be smaller (by 0.3 eV) than that of oxides thicker than similar to 10 Angstrom in accord with the recent XPS results.