Thermally stable fully silicided Hf silicide metal gate electrode

Abstract

A method is described for forming an n-MOSFET with a fully silicided Hf suicide gate electrode that has a work function essentially the same as n.sup.+ polysilicon. An in-situ phosphorous doped polysilicon film is deposited on a gate dielectric layer on a CMOS substrate and annealed at 900.degree. C. After native oxides are removed, a Hf layer is sputter deposited on the doped polysilicon. A W capping layer is formed on the Hf layer to prevent oxidation during a subsequent silicidation. Following the silicidation, W and unreacted Hf are removed. A permanent TaN capping layer is deposited on the HfSi layer to suppress oxidation and reduce sheet resistance. There is no meaningful change in EOT or flat band voltage even after a RTA at 950.degree. C. for 30 seconds. The resulting Hf silicide has a composition ratio of 0.9 according to RBS and has a work function of about 4.23 eV.