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, Ni₂Si, and Ni₃₁ Si₁₂. 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 Ni₂Si 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, Ni₂, and Ni₃₁Si₁₂ 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 Ni₂Si are less than or equal to 25°C, whereas a single-phase Ni₃₁Si₁₂ is obtained over an ∼ 200°C temperature range.