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The positive bias temperature instability (PBTI) and the stress-induced leakage current (SILC) effects are thoroughly examined in nFETs with SiO2/HfO2/TiN dual-layer gate stacks under a wide range of bias and temperature stress conditions. Experimental evidence of the SILC increase with time is obtained suggesting the activation of a trap generation mechanism. Threshold voltage (V T) instability is found to be the result of a complicated interplay of two separate mechanisms; filling of preexisting electron traps versus trap generation each one dominating at different stress condition regimes. Furthermore, V T instability relaxation experiments, undertaken at judiciously chosen conditions, show that the preexisting and stress-induced traps exhibit similar detrapping kinetics indicating that both types of traps may have similar characteristics. Finally, it is shown that the role of the SILC effect (and the associated trap generation component) on V T instability is process dependent and that SILC reduction is accompanied by enhancement of the PBTI device lifetime.
Device and Materials Reliability, IEEE Transactions on (Volume:9 , Issue: 2 )
Date of Publication: June 2009