Anomalous TDDB Statistics of Gate Dielectrics Caused by Charging-Induced Dynamic Stress Relaxation Under Constant–Voltage Stress

Anomalous Time Dependent Dielectric Breakdown (TDDB) statistics of thick gate dielectrics, i.e., too large stress field/voltage dependence and nonlinear Weibull plot of TDDB lifetime, have been observed. Through the analysis of behaviors under the TDDB stress and also the comparison with thin gate dielectrics, it has been revealed that just the intrinsic charging of injected carriers to initial and stress-generated defects induces the dynamic stress relaxation under the constant-voltage stress, resulting in anomalous TDDB statistics. This charging-induced dynamic stress relaxation (CiDSR) effect reduces the validity of well-known Weibull statistics and prevents us from accurately predicting TDDB lifetimes utilizing various conventional scaling procedures, such as area, failure rate, and temperature scaling. Impact of the CiDSR effect increases with the thickness of gate dielectrics and the development of an appropriate lifetime prediction method is urgent not only for Si devices but also for various compound devices having thick gate dielectrics, such as GaN and SiC power devices.