Atomic force microscopy was used for the surface characterization of hard amorphous hydrogenated carbon-nitrogen films deposited by plasma enhanced chemical vapor deposition. The films were deposited onto silicon substrates by rf-plasma decomposition of methane-ammonia mixtures. The film roughness and the friction coefficient between the silicon nitride tip and the film surface were determined. The results indicate that the surface roughness increases with the amount of nitrogen incorporated in the film. The friction coefficients, measured in air, are almost constant for nitrogen incorporation up to 11 at. %.