Linewidth effect and phase control in Ni fully silicided gates

The scalability of Ni fully silicided (FUSI) gate processes to short gate lengths was studied for NiSi, Ni
₂
Si, and Ni
₃₁
Si
₁₂
. It is shown that the control of the deposited Ni-to-Si ratio is not effective for phase and V
_t
control at short gate lengths. A transition to Ni-richer phases at short gate lengths was found for nonoptimized NiSi and Ni
₂
Si processes with excessive thermal budgets, resulting in significant V
_t
shifts for devices on HfSiON consistent with the difference in work function among the Ni silicide phases. Linewidth-independent phase control with smooth V
_t
rolloff characteristics was demonstrated for NiSi, Ni
₂
Si, and Ni
₃₁
Si
₁₂
FUSI gates by controlling the Ni-to-Si reacted ratio through optimization of the thermal budget of silicidation (prior to selective Ni removal). Phase characterization over a wide temperature range indicated that the process windows for scalable NiSi and Ni
₂
Si are less than or equal to 25 degC, whereas a single-phase Ni
₃₁
Si
₁₂
is obtained over an ~200degC temperature range