ANALYSIS OF CUBIC BORON-NITRIDE THIN-FILMS BY NEUTRON DEPTH PROFILING

Cubic boron nitride (c-BN) thin films are of interest in such diverse areas as semiconducting devices, wear resistant coatings, and low friction coatings, owing to the exceptional electrical and mechanical properties of that material. In this work, the boron to nitrogen ratio of thin films produced by physical vapor deposition (PVD) was determined and compared with the crystal phase of BN thin films. Thin films (approximately 0.1 mum) of c-BN were deposited onto heated silicon substrates by electron beam evaporation of boron with concurrent nitrogen and argon ion bombardment. The films were characterized by IR spectroscopy. The stoichiometry of the BN layer was determined by neutron depth profiling (NDP) using the nuclear reactions B-10(n,alpha) Li-7 and N-14(n,p) C-14. Boron-to-nitrogen ratios were determined with uncertainties of 2%-3%. Shifts in IR spectra were observed over a narrow range of boron-to-nitrogen ratios near unity. Stoichiometric results are compared with the crystal phase. Details of the NDP analysis are presented.