Carbon nitride (CNx) thin films have been prepared by cathodic are evaporation of a graphite cathode under simultaneous bombardment of the growing film by a nitrogen ion beam produced by a Kaufman type source. Film deposition was performed varying the ratio of arrival rates of nitrogen and carbon ions, Q(r), the energy of the nitrogen ion beam as well as temperature and bias potential of the substrate. Film composition was analyzed using elastic recoil detection (ERD) analysis. Comparing the fluences of carbon and nitrogen atoms to the number of the respective atoms per unit area found by the ERD analysis, the sticking coefficients for carbon and nitrogen could be obtained. The sticking coefficients are lower than expected for sputtering. Therefore, an additional chemical mechanism has to be assumed. Most probably this mechanism consists of the formation of volatile (CN)(2) supported by the dissociation and excitation of neutral nitrogen species by the are plasma and the ion source. At increasing Q(r) the incorporation of nitrogen is more hampered than that of carbon. This is probably due to the formation and out-diffusion of N-2 molecules.