Interface states for si-based mos devices with an ultrathin oxide layer: X-ray photoelectron spectroscopic measurements under biases

Energy distributions of interface states for <30-Å-thick Pt/25~35-Å-thick silicon oxide/n-Si(100)> metal-oxide- semiconductor (MOS) devices have been obtained from measurements of X-ray photoelectron (XPS) spectra under biases. Upon applying bias voltages, the substrate Si(2p) peak is shifted because of a change in the occupancy of interface states by electrons, inducing a change in the potential drop across the silicon oxide layer. Devices with a native oxide layer have high interface state density near the midgap, which is attributed to isolated dangling-bond states. For MOS devices with a thermal oxide layer grown at 550°C in a wet-oxygen atmosphere, the interface states have two density maxima, one below and the other above the midgap. For devices with a thermal oxide layer formed at 700°C in wet oxygen, two density maxima of the interface states are also observed with reduced density.