Theory of Fermi Level Pinning of High-k Dielectrics

Fermi-level pinning of poly-Si and metal-silicide gate materials on Hf-based gate dielectrics has been systematically studied theoretically. Fermi-level pinning in high-work-function materials is governed by the O vacancy generation and subsequent formation of interface dipoles near gate electrodes due to the electron transfer. On the other hand, O interstitial formation plays a crucial role for Fermi-level pinning in low-work-function materials. From our theoretical considerations, we have found that the work-function pinning-free-region generally appears due the difference in the mechanism of Fermi-level pinning of high- and low-work-function materials. The widening of this work-function pinning-free-region is the key issue for the fundamental relaxation of Fermi-level pinning in high-k gate dielectric