The effects of nitrogen ion implantation on the formation of nickel silicide contacts on shallow junctions have been investigated. The phase formation of nickel silicides on nitrogen implanted (001)Si was suppressed and shifted to a higher temperature compared to samples not implanted with nitrogen. The sheet resistance was found to be nearly constant in a wide range of temperature in nitrogen ion implanted samples. It indicates that low-resistivity NiSi is the dominant phase for the 1 x 10(15) N+/cm(2) implanted samples annealed at 400-750 degrees C and for the 2 x 10(15) N-2(+)/cm(2) implanted samples annealed at 400-800 degrees C. The diffusion of nickel atoms is thought to be retarded by the presence of nitrogen atoms. The presence of nitrogen ion can also improve the thermal stability of nickel disilicide. The effects of nitrogen on nickel silicide formation become more pronounced with an increase in the nitrogen dose up to a certain value.