The Influence of Silicon Surface Defects on MOS Radiation-Sensitivity

The relationships of the electrical properties of irradiated MOS structures to processed-induced surface defects have been investigated. It has been found that the radiation-induced perturbations in oxide space-charge and interface states relate directly to the density of oxidation-induced stacking faults and edge dislocations. The density of such surface defects depends on both the structural properties of the starting silicon and the fabrication procedures. Oxidation-induced stacking faults are strongly related to the oxidation conditions, such as temperature, time, and ambiance. High-frequency CV, quasi-static CV, and ac conductance techniques were used to determine the interface state densities and flat-band voltage distributions. It has been found that, in addition to interface states, exposure to ionizing radiation causes gross non-uniformities in trapped positive space-charge. Using secondary ion mass spectrometry (SIMS) on an MOS sample possessing a high density of stacking faults, it has been shown that positive charge-species drift to the SiO2/Si interface and form clusters in a random fashion similar to that of the defects delineated by differential etching. Based on the known relationship of surface generation lifetime on surface defects pre-irradiation lifetime has been demonstrated as an effective electrical parameter for the prediction of the total-dose radiation sensitivity of MOS devices.