Observation of two gate stress voltage dependence of NBTI induced threshold voltage shift of ultra-thin oxynitride gate p-MOSFET

Abstract

Ultra-fast measurement of NBTI induced threshold voltage shift (|ΔV t |) reveals two |ΔV t | components that exhibit different dependence on the stress time and the gate stress voltage V g s . One component is spontaneously generated upon stress, i.e. fast generation, and the amount generated saturates within the first few seconds of stress. The saturation level is observed to scale linearly with V g s . The second component increases steadily with stress time, i.e. it exhibits a relatively slow generation rate; its stress time dependence may be described by a power-law with exponent n asymptotically approaching ~0.167 at steady state. This component exhibits an exponential/power-law dependence on V g s . Index Terms -negative bias temperature instability (NBTI), ultrafast switching (UFS), threshold voltage I. INTRODUCTIONFast generation and recovery of NBTI induced oxide and interface defects [1] render precise measurement of device degradation very challenging. Though present fast methods significantly minimize measurement induced recovery, they have a wide variation in delay (~10 −6 -10 −3 s). Stress induced degradation of the drain current is typically measured at a relatively large gate voltage and the result is converted to an equivalent |ΔV t | using an I-V model. The accuracy of conversion is limited by the model used and unknown errors [2] (e.g. the effect of stress on mobility, which itself is a function of gate voltage, is not well characterized). Because of these practical difficulties, the exact gate voltage dependence of NBTI induced degradation remains unclear. In this work, we employ an ultra-fast switching (UFS) method [3] for NBTI characterization. The method is readily implemented using a standard parametric tester; it has a very short measurement delay (≤ 100 ns) and a good measurement resolution (~1 µA). These attributes enable the sub-threshold I-V of the transistor to be precisely measured at minimal delay, and |ΔV t | directly determined from the relatively shift in the I-V curves. Through this method, new observations on the gate voltage dependence of NBTI are revealed.

Separation of Hole Trapping and Interface-State Generation by Ultrafast Measurement on Dynamic Negative-Bias Temperature Instability

“…This activation energy corresponds to ∼ T 1.3 dependence on temperature (inset), which is weaker than the T 2 dependence expected of multiphonon-field-assisted tunneling (MPFAT) [4]. We speculate that other forms of hole-trapping/detrapping events (e.g., by elastic tunneling) [2], [10], of weaker thermal activation, may also be occurring in conjunction with MPFAT. Fig.…”