Initial growth steps of ultrathin gate oxides

The studies on the atomic-scale surface roughness, interface structures and interface-state-distribution in silicon bandgap at the initial growth steps of ultrathin oxides formed on Si(100) are reviewed in comparison with ultrathin oxides formed on Si(111). Interface-state-density distribution in silicon band gap was found to change periodically with progress of oxidation in accordance with layer-by-layer oxidation. Therefore, the oxide film thickness must be adjusted with the accuracy of less than 0.1 nm in order to minimize the interface-state-densities. The structural difference between 1-nm-thick structural transition layer and bulk silicon dioxide was detected from the measurement of O1s photoelectron spectra. The effect of elastic scattering on Si 2p photoelectrons in silicon oxide, which is important in the accurate structural analysis of ultrathin gate oxides, is also discussed.