BTI characteristics and mechanisms of metal gated HfO2 films with enhanced interface/bulk process treatments

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 ΔV_t 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.