Charging and Discharging of Oxide Defects in Reliability Issues

Advances in the microelectronic design implicate a reduction of device dimensions requiring a better understanding of the microscopic processes involved. One of these processes concern charging and discharging of defects via tunneling, which is supposed to constitute a grave contribution to various ongoing reliability issues. A deep understanding and a correct modeling of this mechanism are of utmost importance in this context. Conventionally, tunneling levels are believed to remain at fixed positions within the oxide bandgap regardless whether they are occupied or not. From a theoretical point of view, defect energy levels undergo shifts within the silicon dioxide bandgap after charging or discharging. As a result, defect levels for tunneling into and out of traps have to be distinguished. Based on this understanding of trapping, defects can be characterized as fixed charges, switching oxide charges, interface traps, or other types of defects. In this study, we conduct first-principle investigations on the energetics for a series of individual defects encountered in the context of reliability. In order to deduce their tunneling dynamics, a new model. which accounts for the effects of shifting tunneling levels, has been established. On the basis of the E-gamma' center, the main discrepancies between the model relying on trap level shifts and the model with coinciding trap levels have been highlighted.