Impact of Polarity of Gate Bias and Hf Concentration on Breakdown of HfSiON/SiO2 Gate Dielectrics.

We have investigated the impact of polarity of gate bias and Hf concentration on HfSiON/SiO2 gate dielectric breakdown (DB) with time-zero DB (TZDB) and time-dependent DB (TDDB). At TZDB, the gate leakage currents at breakdown (BD) under negative bias are much smaller than those with positive bias without regard to accumulation or inversion states. Since the electric fields at BD are not all the same, the BD mechanism cannot be explained with a simple thermochemical model for all types of stress for HfSiON gate dielectric. With TDDB, the electric-field acceleration constant is dependent on the Hf concentration. Calculated active dipole moments in HfSiON have been shown to be similar to theoretical values for nMOS but not pMOS. Thermochemic BD of HfSiON, itself (not interface SiO2), is adequate to describe nMOS in the inversion state. On the other hand, the BD of pMOS in the inversion state is affected by the carrier currents and not the electric fields as the TZDB. The BD mechanisms are strongly dependent on both the polarity of the gate bias and the Hf concentration. [ABSTRACT FROM AUTHOR]