Microscopic Thickness Uniformity and Time-Dependent Dielectric Breakdown Lifetime Dispersion of Thermally Grown Ultrathin SiO2 Film on Atomically Flat Si Surface

Abstract

Microroughness at the surface and interface of SiO2 thermally grown on an atomically flat Si terrace was investigated by atomic force microscopy. Although surface protuberances on SiO2 increased in height during oxidation, their relative locations were preserved. Their positions were mostly determined in the initial stage of oxidation and their heights increased during the subsequent oxidation. It was also found that, at many positions, protuberances on the SiO2 surface correspond to dimples at the interface and the dimples on the SiO2 surface correspond to the protuberances on the Si/SiO2 interface. With decreasing thickness, the thickness of the SiO2 layer becomes two-dimensionally less uniform. The Weibull slope of the time-dependent dielectric breakdown lifetime decreased when the thermal SiO2 films were grown on rougher Si substrates, which was attributed to film thickness nonuniformity. The SiO2 film formed on well-defined Si wafers showed a higher microscopic thickness uniformity and higher long-term reliability.