Phase effects and short gate length device implementation of Ni fully silicided (FUSI) gates

A study of the implementation of Ni fully silicided (FUSI) gates to scaled devices is presented, addressing the issue of phase control at short gate lengths. A linewidth effect for Ni FUSI gates is found for non-optimized processes targeting NiSi, with formation of NiSi at long gate lengths and Ni-rich silicides at short gate lengths. This is attributed to Ni diffusion from areas surrounding the gates, resulting in a larger reacted Ni–Si ratio at short gate lengths. The linewidth dependence of the Ni FUSI phase results in an undesirable kink in the Vt roll-off characteristics, due to the difference in effective work function between the Ni silicide phases, which is particularly large for HfSiON dielectrics. An optimized 2-step RTP silicidation process is shown to eliminate this problem allowing the formation of NiSi gates uniformly at all gate lengths. The application and scalability of Ni-rich silicides to PMOS devices is also demonstrated, as well as a scheme for CMOS integration of dual WF phase controlled FUSI (NiSi for NMOS and Ni-rich silicides for PMOS), using an etch back step to reduce the poly-Si height on PMOS electrodes before full silicidation.