Suppression Effects of Threshold Voltage Variation with Ni FUSI Gate Electrode for 45nm Node and Beyond LSTP and SRAM Devices

We have found that fully silicided (FUSI) gate is a promising technology for the first time not only for breaking the gate stack scaling limitation on low standby power (LSTP) devices but for keeping continuous scaling of high density SRAM (HDSRAM) for 45nm node and beyond. It is shown that FUSI will drastically suppress the fluctuation of threshold voltage (Vth) of fine transistors of HDSRAM. We have confirmed that FUSI gate drastically decreases the Vth variation which is caused by high impurity concentration of channel region and inter-diffusion of gate doping between nMOSFET and pMOSFET, both are essential and unable to be avoided. These parts of Vth fluctuation are suppressed to the degree that HDSRAM will be scaled on the ongoing trend by utilizing FUSI gate.