Theoretical models for work function control (Invited Paper)

Abstract

We have studied Fermi level pinning (FLP) of Hf-based high- k gate stacks based on thermodynamics based on an O vacancy model. Our study shows that FLP cannot be avoided when the system is under thermal equilibrium. O exposure to aim O vacancy elimination is not effective, since O vacancy elimination condition is equivalent to the Si substrate oxidation which leads to the increase in Equivalent oxide thickness (EOT). We also studied the mechanism of FLP induced by the reduction with H 2 anneal. FLP with H 2 anneal is governed by the O vacancy annihilation reaction by reducing SiO 2 interface layer. Based on these considerations, we propose some recipes for obtaining band-edge-work-function metals.