Consideration of recovery effects during NBTI measurements for accurate lifetime predictions of state-of-the-art pMOSFETs

The NBTI recovery phenomenon leads to a fast reduction of the stress induced electrical device parameter degradation after end of stress. Delay times between device-stress and -characterization within NBTI-experiments affect the measurement values of degradation. This work discusses the impact of these delays on lifetime prediction for technology qualifications. For this reason we investigate delay times from 1mus up to 60s and stress times from 100ms up to 250000s. A correlation between stress time, delay time induced recovery and error in predicted lifetime is elaborated for the first time. The influence of the recovery on single device stress experiments, on the voltage acceleration and finally on lifetime extrapolation is discussed. Furthermore we give simple guidelines for measurement requirements and essential stress times for accurate lifetime evaluations.