Improvement on sheet resistance uniformity of nickel silicide by optimization of silicidation conditions

The formation of high resistivity phases of nickel silicide in a small silicide area is a problem for the uniformity of the sheet resistance. It was found that implementing furnace annealing method, as the first annealing step, improves the nickel silicide sheet resistance uniformity at small areas. Low ramp rate and prolonged annealing duration by furnace anneal promote grain size growth of Ni2Si phase, which decreases the free energy change and suppresses the formation of high resistivity phases of nickel silicide. Increasing the first anneal temperature was also found to improve the sheet resistance uniformity of only p+ active areas. Furthermore, increasing the temperature of Ni PVD stage or second anneal, promotes the formation of NiSi2 phase.