Fast and accurate method of lifetime estimation for HfSiON/SiO2 dielectric n-MOSFETs under positive bias temperature instability

Abstract

This paper proposes a fast and accurate method to measure the constants a and n of the power law ∆Vth=atn for HfSiON/SiO2 dielectric nMOSFETs under positive bias temperature instability (PBTI), where ∆Vth is a shift of threshold voltage, and t is stress duration. The proposed method requires one nMOSFET only, uses a voltage ramp stress (VRS), measures ∆Vth vs. t data during VRS, uses a regression method to fit the data for each VRS pulse to the power law to obtain a and n at each stress voltage Vg,str, then obtains five voltage-independent constants for the power law after fitting the curves of a and n vs. Vg,str to empirical models. The five voltage-independent constants agreed very well with those obtained using the constant voltage stress (CVS) method. After obtaining the voltage-independent constants, the lifetime tL at an operating voltage Vop was estimated using the power law. The estimated tL=1.67×108s was quite close to tL=1.74×108s estimated using CVS, and to tL=1.72×108s estimated by extrapolating the ΔVth vs. t curve measured at Vg,str=Vop=1.2V to ΔVth=200mV. The time required for measurement was 900s, compared to 30,000s for the CVS method. These experimental results show that the proposed VRS-regression method is very useful for screening nMOSFETs under PBTI.