Thermal Instability of Effective Work Function in Metal/High- $kappa$ Stack and Its Material Dependence

Thermal instability of effective work function and its material dependence on metal/high-/spl kappa/ gate stacks is investigated. It is found that thermal instability of the effective work function of metal electrode on a gate dielectric is strongly dependent on the gate electrode and dielectric material. Thermal instability of a metal gate is related to the presence of silicon at the interface, and the Fermi-level pinning position is dependent on the location of silicon at the interface. The silicon-metal or metal-silicon bond formation by thermal anneal at the metal/dielectric interface induces the donor-like or acceptor-like interface states, causing a change of effective work function.