The effect of capping layer (Ti vs TiN) on CoSi formation and CoSi2 sheet resistance has been investigated. Resistance measurements and XTEM analysis have been used to show that the Ti cap lowers the activation energy for CoSi formation by gettering the O2 from the RTA (rapid thermal anneal) ambient and eliminating the formation of SiO2 between the growing CoSi and the Co. The sheet resistance of cobalt silicide formed from Co/Ti and Co/TiN bilayers on poly- Si lines was measured as a function of linewidth and RTA temperature. With a Ti cap, the sheet resistance is low and independent of temperature, and the RTA process window is large.