Paper SS-ThP24
Formation and Collapse of Au/n-Si Schottky-Barrier Contact at the SiO₂/Si Interface and Oxidation Kinetics in Au-Contaminated and Thermally Oxidized n-Si (001) Surfaces

Thursday, October 23, 2008, 6:00 pm, Room Hall D

We have investigated an anomalous profile of Au in SiO₂/Si region as a function of oxidation temperature and then clarified an oxidation mechanism utilizing ellipsometer, X-ray photoelectron spectroscopy (XPS) and alternating current surface photovoltage (AC SPV) methods. When n-type Si wafers having hydrophobic surface were rinsed in Au aqueous solution (the Au surface concentration = ~2 1015 atoms/cm2) and then thermally oxidized at between 550 and 750C, an Au cluster still resided both at the SiO₂/Si interface and the top area of SiO₂ film. Most of the Au at SiO₂/Si was identified to be detected as the Au cluster which did not make bonds with other elements such as O, H and Si. The Au at the SiO₂/Si interface formed Au/n-Si Schottky-barrier, causing depleted and/or inverted layer at the Si surface, thereby, giving rise to an occurrence of a frequency-dependent AC SPV. As the oxidation temperature and time increased, the frequency-dependent AC SPV decreased and disappeared, corresponding to the fact that the Au cluster at SiO₂/Si interface decreased and/or disappeared. At oxidation temperatures higher than at 750~800 C, the frequency-dependent AC SPV was not detected. The Au was found to diffuse deeper in both SiO₂ bulk and Si substrate as the oxidation advanced. Regarding oxidation kinetics at between 550 and 900C, Au caused a drastic SiO₂ growth enhancement for SiO₂ thickness less than ~10 nm. This result shows that Au acted as catalyst to promote the initial SiO₂ growth at the Si(001) surface. The behavior of the Au in SiO₂ layer explained the relationship between oxide thicknesses and oxidation time. Finally, the SiO₂ growth mechanism influenced by the addition of Au is proposed.