Correlation between midgap interface state density and thickness-averaged oxide stress and strain at Si/SiO2 interfaces formed by thermal oxidation of Si

Correlations between midgap interface state density (Dit) and thickness-averaged stress in thermally grown SiO2 thin films have been investigated by infrared spectroscopy, an optical beam deflection technique, and capacitance-voltage measurements. We find no correlations between Dit and either (i) the maximum stress in the Si or SiO2 at the Si/SiO2 interface or (ii) the stress gradient in the SiO2 film. By direct measurements of the strain-induced bending of the Si wafer, and by calculating the microscopic strain from the SiOSi bond-stretching vibrational frequency, we have established linear relationships between Dit and the thickness-averaged stress and strain in the oxide.