We apply a systematic approach to identify a highk/metal gate stack degradation mechanism. Our results demonstrate that the SiO 2 interfacial layer controls the overall degradation and breakdown of the high-k gate stacks stressed in inversion. Defects contributing to the gate stack degradation are associated with the high-k/metal-induced oxygen vacancies in the interfacial layer.

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Breakdown characteristics of Hf-based high-k dielectrics in a wide thickness range were investigated to identify the "weak link" in the gate stack and its leading breakdown mechanisms under inversion stress. A strong correlation among the growth rates of the stress leakage current, SILC, and interface trap density suggests that breakdown is triggered by trap generation in the interfacial SiO2 layer. Stress-time evolution of the differential resistance and its slope obtained from SILC data allows progressive breakdown in highk/metal gate stacks to be identified.

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A methodology to analyze charge pumping (CP) data, which allows positions of probing traps in the dielectric to be identified, was applied to extract the spatial profile of traps in SiO2∕HfO2 gate stacks. The results suggest that traps accessible by CP measurements in a wide frequency range, down to few kilohertz, are located within or near the interfacial SiO2 layer rather than in the bulk of the high-k film.

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Positive bias constant voltage stress combined with charge pumping (CP) measurements were applied to study trap generation phenomena in SiO 2 /HfO 2 /TiN stacks. Using gate stacks with varying thicknesses of the interfacial SiO 2 layer (IL) or high-κ layer and analysis for frequency-dependent CP data developed to address trap depth profiling, the authors have determined that the defect generation in the stress voltage range of practical importance occurs primarily within the IL on as-grown "precursor" defects most likely caused by the overlaying HfO 2 layer. The generated traps can be passivated by a forming gas or nitrogen (N 2 ) anneal, whereas a postanneal stress reactivates these defects. The results obtained identify the IL as one of the major targets for reliability improvement of high-κ stacks.