Effect of Germanium on Solid-Phase Reaction and Effective Work Function in Fully Ni-Germanosilicided [Ni(Si1 − xGex)] Gate

Fully Ni-germanosilicided [Ni(SiGe)] gate electrode was systematically investigated by means of both structural analyses and electrical measurements. The authors fabricated Ni(SiGe)-gated MOS capacitors with various Ge fractions through the solid-phase reaction at Ni/polycrystalline SiGe (poly-SiGe) interface. It was found that Ge atoms can only be dissolved in NiSi phase, and then Ni(SiGe) phase is formed. In addition, even in the case that the thickness ratio of Ni to Si is equivalent to that required to form Ni₂Si, Ge atoms induce phase change from Ni₂Si to Ni(SiGe) near SiO₂ interface. This phenomenon promotes condensation of Ge atoms in Ni(SiGe). The values of effective work function (Phi_eff) are independent of the Ge fraction in the low Ge fraction (Ge < 60%) Ni(SiGe) gate. On the contrary, the Phi_eff values begin to change to values larger than that of NiSi in the case of a Ge fraction higher than 60%. In addition, the Ge incorporation modulates the Phi _eff shift effect of piled-up B atoms to the opposite direction compared to the NiSi cases reported previously. As a result, the controllable Phi_eff range for piled-up B atoms can be expanded to 0.47 eV near the Si midgap