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This paper reports significantly improved charge trapping lifetime of HfOz nMOSFETs by using TaSiN gate instead of polySi gate. It will demonstrate that the trapping induced threshold voltage shift is much more of a concem than TDDB in determining the device operating lifetime. A trapping model with a continuous distribution in trapping capture cross section has been used to extrapolate the device lifetime. Charge pumping results suggest the improvement on trapping lifetime is due to reduced bulk trap density in TaSiN gated HfO2 nMOSFETs.

This paper focuses on a major reliability issue for Hf-based high-k gate dielectrics. It will show that (1) the operating lifetime extracted from the trapping induced threshold voltage shift, ∆V th , is much shorter than that extracted from Time-Dependent Dielectric Breakdown, and therefore the actual device lifetime is limited by charge trapping; (2) Biased in inversion, electron trapping is the dominant mechanism for nMOSFETs; hole trapping is the dominant mechanism for pMOSFETs at low voltages (< 2 eV); (3) for pMOSFETs biased at high voltages (> 2.6 V), either net electron trapping or net hole trapping are observed, depending on the details of the stress conditions; (4) the above can be explained by the electron and hole currents through the dielectric for a given stress condition; (5) electron traps (with the energy level at ~0.68eV below E c of the dielectric) give rise to Frenkel-Poole (F-P) conduction; (6) hole traps do not participate in F-P conduction in the temperature range studied (300-500 k).

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