Bias-temperature instabilities of polysilicon gate HfO2 MOSFETs

Bias-temperature instabilities (BTI) of HfO₂ metal oxide semiconductor field effect transistors (MOSFETs) have been systematically studied for the first time. NMOS positive BTI (PBTI) exhibited a more significant V_t instability than that of PMOS negative BTI (NBTI), and limited the lifetime of HfO₂ MOSFETs. Although high-temperature forming gas annealing (HT-FGA) improved the interface quality by passivating the interfacial states with hydrogen, BTI behaviors were not strongly affected by the technique. Charge pumping measurements were extensively used to investigate the nature of the BTI degradation, and it was found that V_t degradation of NMOS PBTI was primarily caused by charge trapping in bulk HfO₂ rather than interfacial degradation. Deuterium (D₂) annealing was found to be an excellent technique to improve BTI immunity as well as to enhance the mobility of HfO₂ MOSFETs.