The possibility of controlling the growth of nickel silicide by implanting N into thin Ni films evaporated on Si substrates has been studied using4He backscattering spectrometry. The reaction between Ni and Si is completely halted below annealing temperatures of ∼375 °C by implanted doses of 5×1016N/cm2. At higher annealing temperatures, localized intermixing takes place. For low doses ≲0.5×1016N/cm2, the reaction between Ni and Si is that observed for unimplanted samples both in the phase formed (Ni2Si) and in rate of growth. For intermediate doses ∼0.9×1016N/cm2, the first phase formed corresponds to NiSi, and the growth rate is greatly reduced. These results are explained in terms of a silicon nitride barrier to Ni diffusion forming at the Ni/Si interface.