The effects of nitrogen ion implantation on CoSi2 contacts on shallow junctions have been investigated. The formation, growth, stability and resistivity of suicides as well as the removal of residual defects have been studied. Nitrogen ion implantation was shown to improve the thermal stability of CoSi2 thin films. The sheet resistance was found to be nearly constant in a wide range of temperature in N+ implanted samples. For Co on 30 keV N+ implanted samples, a continuous and pinhole-free polycrystalline CoS2 layer was found to form in all samples after annealing at 700-900 °C. The thermal stability of the CoSi2 layer in tha BFN2+-N+ samples was better than samples implanted with N + or As+-N+. The improvement in the thermal stability and surface morphology of CoSi2 in BF2+-N+ samples is attributed to the presence of fluorine bubbles at CoSi2 grain boundaries, which impeded the grain growth.