Effect of HfSiON thickness on electron trap distributions of HfSiON/SiO2 nMOSFET under PBTI

Abstract

The effect of HfSiON thickness on electron trap distributions under positive bias temperature instability (PBTI) was investigated in HfSiON/SiO2 nMOSFET. Trap distributions of HfSiON/SiO2 nMOSFET were observed by charging and discharging electrons at pre-existing or newly-generated traps. Experimental results show that the peak values of electron trap density shifted to deeper electron trap energy level (E-t) with increasing stress field E-str and stress time t(s). Compared to the Thick HfSiON device, the Thin HfSiON device had lower trap density and slower Et-shift; as a result, the Thin HfSiON device had lower threshold voltage-shift Delta Vth and larger power-law time exponent n of PBTI than the Thick HfSiON device. Low Delta Vth is beneficial for lifetime of HfSiON/SiO2 nMOSFET but large n is not, so the effect of HfSiON thickness on distribution of electron trap must be quantified to enable optimization of HfSiON thickness to yield reliable HfSiON/SiO2 nMOSFETs.