Use of the Subthreshold Behavior to Compare X-Ray and CO-60 Radiation-Induced Defects in MOS Transistors

Transistor behavior in the subthreshold region is used to compare the production of oxide trapped charge and interface states produced by x-ray and Co-60 radiation. For the oxides used in this study, the subthreshold data indicates the presence of two types of interface states. One of these interface states appears to differ from the more commonly observed amphoteric defect. The characteristics of these states suggest that they are donor defects. These states further complicate testing protocols because they anneal at room temperature. A modification to the subthreshold measurement technique of McWhorter and Winokur is proposed for oxides in which these donor states occur. Using this revised subthreshold technique, less interface dose enhancement occurs during x-ray exposures than was observed previously with thick-oxide-capacitor measurements.