Impact of silicide formation on the resistance of common source/drain region

Silicide had been used to reduce the sheet resistance of diffusion region for almost 20 years. However, as the silicided region becomes small, the contact resistance of silicide/silicon interface becomes higher than the resistance of the Si diffusion region such that current may not flow into the silicide layer. The effect of silicide thickness and contact resistivity on the total resistance of the silicided diffusion region was studied by two-dimensional simulation. It is observed that below a threshold length, the resistance of silicided diffusion region is higher than the unsilicided diffusion region if the silicon consumption during silicide formation is taken into consideration. Thinner silicide and lower contact resistivity reduce total resistance and threshold length but the threshold length is still much longer than the typical design rule of poly-Si to poly-Si distance. It is thus recommended to inhibit silicide formation at the common source/drain region at the metal-gate generation.