Correlation between Interface States and Structures Deduced from Atomic-Scale Surface Roughness in Ultrathin SiO2/Si System

Abstract

Since MOSFETs with a gate oxide film thickness of 1.5 nm were shown to operate at room temperature [1], extensive studies have been performed on the reliability of ultrathin gate oxides. [2] Because the thickness of the structural transition layer is in the order of 1 nm [3,4] and the amount of electronic defect states in the structural transition layer must be larger than that in bulk SiO2, the reliability of gate oxides must be mainly determined by the chemical structures of compositional and structural transition layers. In spite of the extensive studies on the interface states and structures, the structural origin of interface states has not yet been explained. [5] This is because of the difficulty of two-dimensional atomic-scale observation of interface structures and the two-dimensional atomic-scale detection of interface states. In the present study the dependence of the atomic-scale surface roughness of ultrathin oxide on oxide film thickness was measured. This enabled the effect of the interface structure on the atomic-scale surface roughness to be clarified on an atomic-scale. The effect of the interface structure on the interface electronic states and the valence band structure were also studied.