Phase stability and stress relaxation effects of cubic boron nitride thin films under 350 keV ion irradiation

To investigate the effect of radiation damage on the stability and the compressive stress of cubic boron nitride (c-BN) films, samples either prepared by r.f. magnetron sputtering or ion beam-assisted sputter deposition (IBAD) were irradiated at room temperature with 350 keV inert ions (Kr+). FTIR spectra taken before and after each irradiation step clearly demonstrate that c-BN is stable under this medium energy bombardment. Furthermore, additional AES measurements show that the average film stoichiometry is not affected by the ion fluences used in the present experiments. While the observed broadening of the different lines in the IR spectra with increasing ion fluences points to a build-up of disorder and/or a decreasing average grain size due to the bombardment, the additionally found significant shift of the line related to the c-BN TO-mode towards smaller wave numbers, indicates a strong relief of the compressive stress present in the as-prepared films. This irradiation-induced stress relief could be independently confirmed by profilometer measurements yielding post-bombardment values of 5.1 GPa as compared to 20.5 GPa before irradiation. (C) 1997 Elsevier Science S.A.