Contactless capacitance-voltage and photoluminescence characterization of ultrathin oxide-silicon interfaces formed on hydrogen terminated (111) surfaces

Electronic properties of the interfaces between Si and ultrathin (less than or similar to 10 Angstrom) oxides formed by various low-temperature processes were characterized in contactless fashion, using contactless capacitance-voltage and photoluminescence surface state spectroscopy techniques together with x-ray photoelectron spectroscopy measurement. Hydrogen (H) terminated Si(111) surfaces were used as the initial surface. Ultrathin oxides were formed at low temperatures by chemical oxidation processes (hot HNO3, H2SO4+H2O2), long-time air exposure, and low-temperature oxidation processes below 350 degrees C. The initial H-terminated surfaces showed presence of Fermi-level pinning at E(0)=E(V)+0.65 eV due to high density of amphoteric discrete state probably originating from Si dangling bonds. On the other hand, all the ultrathin oxide-Si interfaces exhibited very limited capacitance variations with voltage at low capacitance levels similar to GaAs metal-insulator-semiconductor systems, and indicated that the Fermi level is pinned near the hybrid orbital charge neutrality level E(HO) due to presence of interface states with narrow U-shaped continuous distributions. Low-temperature oxidation at 350 degrees C slightly weakens such pinning. The present work indicates difficulty of realizing unpinned ultrathin oxide-silicon interface by low-temperature processes. (C) 1996 American Vacuum Society.