The self-aligned-silicidation technique has become a crucial part of ultra-high speed CMOS technologies. Many studies on NiSi have been reported recently. NiSi possesses many advantages and appears to be a suitable candidate to replace TiSi2 in future ULSI devices. Nitrogen ion implantation has been used to suppress the boron and arsenic diffusion as well as hot-carrier degradation. In this paper, the formation of Nickel silicides on nitrogen ion implanted silicon is investigated. The phase formation of nickel silicides on nitrogen implanted (001) Si was suppressed and shifted to a higher temperature compared to that of blank sample. The presence of nitrogen ion was found to improve the crystallinity of epitaxial NiSi2. The effects of nitrogen on nickel silicide formation become more pronounced with the increase in the dose of nitrogen implantation.