Effects of interface roughness on the density of interface states at ultrathin oxide/Si interfaces: XPS measurements under biases

The energy distribution of interface states for MOS devices with atomically smooth and rough Si(l1 II/ultrathin oxide interfaces was obtained from measurements of X-ray photoelectron spectra under biases between the metal overlayer and the Si substrate. The interface state density for the smooth interface is always lower than that for the rougher interface. Synchrotron radiation ultraviolet photoelectron spectra show that the amount of the Si2+ species in the oxide layer is reduced by forming a smooth interface. It is proposed that the Si2+ species at step edges hinder the formation of complete SiO, networks, resulting in the production of Si dangling bond interface states near them.