Raman scattering of cubic boron nitride films deposited from the low-pressure gas phase

By introduction of the chemical effects of fluorine, thick cubic boron nitride (cBN) films with high phase purity and low residual stress were synthesized on silicon substrates by dc-bias-assisted dc jet chemical vapor deposition in an Ar–N₂–BF₃–H₂ system. In this paper, the characterization of the films by scanning electron microscopy, glancing-angle x-ray diffraction, infrared spectroscopy, and Raman spectroscopy was done. Among these techniques, Raman spectroscopy was intensively studied, and a method was established to evaluate the crystallinity and residual stress of the cBN films from the line width and peak shift of Raman charactersitic peaks. The influences of the experimental parameters, i.e., bias voltage, substrate temperature, and deposition time, on the film quality were systematically studied. An experimental window for the deposition of cBN films was described. The cBN films deposited under optimized conditions showed the similar line width of both Raman TO and LO modes and thus a crystallinity comparable to that of 4–8-μm cBN single crystals synthesized by high-ressure and high-temperature methods.