The constitution and properties of cubic boron nitride thin films: a comparative study on the influence of bombarding ion energy

Boron nitride thin films were deposited by unbalanced radio frequency magnetron sputtering of a hot-pressed hexagonal boron nitride target in a mixed argon/nitrogen atmosphere of 0.2 Pa. The intensity of ion bombardment during deposition was varied by a direct current substrate bias between 0 and −500 V. Thin films containing more than 85% of the sp3-bonded cubic phase (c-BN), as confirmed by infrared spectroscopy, were produced in a wide voltage range from −200 to −400 V. The high c-BN content can be maintained even at an appreciably reduced bias of −80 V when a nucleation layer is formed in advance. In that case a decrease of compressive stress as well as an alteration of surface structure of the deposited c-BN films was observed. An analysis in light of electron energy loss spectroscopy indicates moreover the existence of an sp2-coordinated surface layer with an ion-energy-dependent thickness. The results are discussed within the frame of the subplantation model.