Optimization of nitrogenated amorphous carbon films deposited by dual ion beam sputtering

Optimization of deposition conditions for nitrogenated amorphous carbon (a-C:N) films prepared by a dual ion beam sputtering (DIBS) technique is reported. A ripple structure was observed on the surface of a-C:N films, which was believed to be corresponding to the off-normal incidence bombardment by N ions during deposition. Infrared spectra indicated that the nitrogen atoms incorporated were bonded as C–N, CN and CN in the carbon network. The relative intensity of D and G bands obtained by fitting the Raman spectra showed that the sp3 content in the a-C:N films increased as the Ar ion energy was increased and the sp3 content was the highest with 100 eV N ion bombardment. The maximum micro-hardness achieved was about 25 GPa for the 200 nm thick a-C:N films deposited under the optimized conditions. The compressive stress ranged from 1 to 3 GPa. The optical band gap determined by spectral ellipsometry ranged from 0.6 to 1.0 eV. The refractive index and extinction coefficient at 633 nm wavelength were about 2.14 and 0.22 for the films deposited under the optimized conditions, respectively. Hardness, stress and optical band gap measurements showed a similar trend with the relative intensity of ID/IG.