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-Angstrom-thick Pt/25 similar to 35-Angstrom-thick silicon oxide/n-Si(100)] metal-oxide-semi conductor (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 occup ancy of interface states by electrons, inducing a change in the potent ial drop across the silicon oxide layer. Devices with a native-oxide l ayer have high interface state density near the midgap, which is attri buted to isolated dangling-bond states. For MOS devices with a thermal oxide layer grown at 550 degrees C in a wet-oxygen atmosphere, the in terface states have two density maxima, one below and the other above the midgap. For devices with a thermal oxide layer formed at 700 degre es C in wet oxygen, two density maxima of the interface states are als o observed with reduced density.