Impact of Mixed Negative Bias Temperature Instability and Hot Carrier Stress on MOSFET Characteristics—Part II: Theory

Abstract

Bias temperature instability (BTI) and hot-carrier degradation (HCD) are among the most important reliability issues but are typically studied independently in an idealized setting. However, even though it is well understood that mixed BTI/HC degradation corresponds to a realistic scenario, there is only a limited number of studies available on the impact of mixed stress conditions. In this first part of the work, we present a thorough experimental study of the impact of mixed stress conditions on SiON pMOSFET characteristics, which contain a study at the single defect level. We focus on the contribution of single defects to the recoverable component of degradation. From an electrostatic point of view, recovery after mixed negative BTI (NBTI)/HC stress is typically attributed to charge carrier emissions by oxide defects near the source, which have been charged during stress. However, the experimental characterization of recovery after different stress conditions provides strong evidence that even defects located in the vicinity of the source can remain uncharged after mixed NBTI/HC stress, and thus do not contribute to the recovery signal. Consequently, the recoverable component can be negligibly small after certain stress conditions, which leads to the conclusion that a simple electrostatic model does not properly describe the behavior of recovery after mixed NBTI/HC stress.