Nitrogen implantation prior to nickel silicidation is shown to result in a modified Schottky barrier height at the NiSi/Si(001) interface. Passivation of dangling bonds at the NiSi/Si interface to de-pin the Fermi level, axiotaxy texture, and strain-induced barrier lowering are determined to be the main mechanisms for the barrier-height modification. Significant barrier-height reduction (by as much as 0.37 eV) can be achieved on n-type silicon. However, the resistivity of nickel silicide increases significantly beyond a critical nitrogen-implant dose (1x10(15) cm(-2)).