Tunable work function in fully nickel-silicided polysilicon gates for metal gate MOSFET applications

The work function of fully nickel-silicided polysilicon was investigated. The midgap work function (4.7 eV) was obtained for undoped mononickel-silicide (NiSi). It was shown that the implantation of both arsenic and antimony into the polysilicon before silicidation reduces the NiSi work function, and the change in work function is greater for antimony than for arsenic. The pile-up of these species at the oxide interface during the nickel silicidation is demonstrated to be the physical mechanism responsible for the work function shift. Both species activations before silicidation and silicidation conditions were found to affect the NiSi work function shift significantly. The nonactivated species have minimum effect and incomplete silicidation can have maximum work function shift. The doping effect of indium on the NiSi work function is reported for the first time. A shift of ∼0.14 eV toward the valence band was obtained for 2.6-nm oxide capacitors. It was found that the work function shift caused by the indium doping is saturated at a relatively low dose, which may be related to the low solid solubility of indium in polysilicon.