Evidence That Two Tightly Coupled Mechanisms Are Responsible for Negative Bias Temperature Instability in Oxynitride MOSFETs

Negative bias temperature instability (NBTI) is a serious reliability concern for pMOS transistors. Although discovered more than 40 years ago, the phenomenon remains highly controversial in both experimental and theoretical terms. A considerable number of recent publications suggest that NBTI is caused by the following two independent mechanisms: 1) generation of defects close to the silicon/silicon dioxide interface and 2) hole trapping in the oxide. We have performed stress and recovery experiments at different temperatures and voltages that, quite surprisingly, reveal that all data can be scaled onto a single universal curve during stress, recovery, and restress. This suggests that in our samples, NBTI is caused by either a single dominant mechanism, which is more complicated than previously anticipated, or that the previously suggested mechanisms, i.e., hole trapping and defect creation, are actually tightly coupled.