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Our recent investigations and understanding of the negative bias temperature instability (NBTI) degradation in p-MOSFETs with ultrathin SiON gate dielectric are reviewed. The progressive understanding of NBTI mechanism is mainly related to the novel measurement techniques we developed. We show in this paper the following: 1) For the conventional charge pumping and direct-current current-voltage interface trap measurement, the interface trap density Nit is underestimated due to the recovery during measurement delay. The existing Nit data should be reexamined; 2) an ultrafast pulsed I-V method [fast pulsed measurement (FPM)] is developed to measure DeltaVth with measurement time tM = 100 ns. It can be considered as free from recovery during measurement; 3) due to the degradation during the initial threshold voltage measurement, the existing slow on-the-fly (OTF) DeltaVth measurement distorts (overestimates) the slope and induces a kink at early stress time in the Log-Log curve of the time evolution of NBTI degradation. A fast OTF DeltaVth measurement method is developed to overcome this problem; 4) a novel OTF interface trap (OFIT) measurement method is developed which is free from interface trap recovery during measurement. The OFIT measurement provides the most reliable data to inspect the interface trap R-D model; 5) combining the OFIT and FPM measurements, we decompose the NBTI DeltaVth into two components: A slow DeltaVth it component contributed by with a slow recovery time longer than 50mus and a fast DeltaVth ox component contributed by DeltaVox with a broad spectrum of recovery time, including a component with very fast recovery time (100 ns); and 6) the dynamic degradation by DeltaVth it component is frequency-independent and can be measured by a dc method, whereas the dynamic degradation DeltaVth ox by component measured by FPM is increased by increasing frequency. The ten-year lifetime of the p-MOSFETs is mainly determined by the degradation of the DeltaVth it component.
Device and Materials Reliability, IEEE Transactions on (Volume:8 , Issue: 1 )
Date of Publication: March 2008