Importance of heat-up ramp rate for palladium-silicide fully-silicided-gate structure formation

Silicidation process for fully-silicided (FUSI) Pd/sub 2/Si gate formation has been investigated. Two types of heating equipment was used for siliciding palladium deposited on a poly-Si/SiO/sub 2//Si MOS structure. One is lamp heating in a sputtering chamber and another is hot-plate heating. The former provide slower heat-up ramp because of relatively large thermal capacity. In this case, metal-rich phase was formed in the first stage of silicidation and it changed to Pd/sub 2/Si phase by additional heating after completion of silicidation reaction. FUSI utilizes impurity pre-doping to poly-Si to modulate workfunction. Pre-doping to poly-Si sometimes resulted in needle structure formation on a top of silicided film and voids at the interface between silicide and SiO/sub 2/. These defects were reduced by silicidation with hot plate heating. In addition, Pd/sub 2/Si phase was obtained at the early stage of silicidation. Palladium and silicon reacts even at temperatures lower than 250/spl deg/C. Therefore, in the case of the lamp heating, silicidation during heating is not negligible. These results are explainable considering change of major diffusion species during silicidation.