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Significant deviations in BTI characteristics for metal gate HfO2 films compared to silicon oxide based films prove that conventional reliability models based on SiO2 films can no longer be directly applied to HfO2 based MOSFETS. This study shows the use of conventional accelerated reliability testing in the Fowler-Nordheim tunneling regime to extrapolate time to failure at operating voltages (direct tunneling regime) overestimates device lifetimes. Additionally, unlike conventional gate oxides, the slope of ΔVt versus time (or the rate of charge trapping) in HfO2 MOSFETS is dependent on stress voltage. The HfO2 based metal gated nMOSFETS show poor PBTI characteristics and do not meet the 10 year lifetime criterion for threshold voltage stability. On the other hand, HfO2 based pMOSFETS show superior NBTI behavior and meet the 10 year lifetime criterion. These results are contrary to the observations with conventional gate dielectrics. This paper explores the anomalous charge trapping behavior and provides a comprehensive study of the PBTI characteristics and recovery mechanisms in metal gated HfO2 films.
Device and Materials Reliability, IEEE Transactions on (Volume:5 , Issue: 1 )
Date of Publication: March 2005