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 Delta V-th = at(n) for HfSiON/SiO2 dielectric nMOSFETs under positive bias temperature instability (PBTI), where Delta V-th 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 Delta V-th 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 V-g,V-str,,then obtains five voltage-independent constants for the power law after fitting the curves of a and n vs. V-g,V-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 t(L) at an operating voltage V-op was estimated using the power law. The estimated t(L) = 1.67 x 10(8) s was quite close to t(L) = 1.74 x 10(8) s estimated using CVS, and to t(L) = 1.72 x 10(8) s estimated by extrapolating the Delta V-th vs. t curve measured at V-g,V-str = V-op = 1.2 V to Delta V-th = 200 mV. The time required for measurement was 900 s, compared to 30,000 s for the CVS method. These experimental results show that the proposed VRS-regression method is very useful for screening nMOSFETs under PBTI.