Sensitivity of contactless transient spectroscopy and actual measurement of localized states in oxidized Si wafer

Abstract

The detection sensitivity of contactless transient spectroscopy (COLTS) to localized states was investigated in detail. We first point out that the detection sensitivity of conventional capacitance transient spectroscopy to interface traps is greatly degraded as oxide thickness is very thin. This is a serious problem for the electrical characterization of recent MOS devices with an ultra-thin gate oxide. In this study, we found that COLTS measurements could overcome this problem: we determined that high detection sensitivity to the interface traps could be maintained using an optimal air gap in the COLTS measurements even when the oxide film is very thin. This is because maximal sensitivity is obtained at the optimal oxide thickness of around 300 nm in conventional capacitance transient spectroscopy. This shows that COLTS can become a highly sensitive tool for interface traps in advanced MOS devices with an ultra-thin gate oxide. In addition, actual COLTS measurements were performed using an oxidized n-type Si wafer doped with gold impurity. Experimental results support the dependence of the detection sensitivity on an air gap which is predicted by theoretical calculation.