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 Ni31Si12. 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 Vt 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, Ni2Si, 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 degrees C, whereas a single-phase Ni31Si12 is obtained over an -200 degrees C temperature range.