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 (Et) with increasing stress field Estr and stress time ts. 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 ∆Vth and larger power-law time exponent n of PBTI than the Thick HfSiON device. Low ∆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.