Characterization of ion-assisted pulsed laser deposited cubic boron nitride films

Cubic boron nitride films were deposited by pulsed laser deposition from a boron nitride and a boron target using a KrF-excimer laser, where the growing films were bombarded by a nitrogen or a nitrogen/argon ion beam. The variation of the film properties with laser and ion beam parameters and substrate temperature has been investigated by infrared spectroscopy, cross-section and plan-view high-resolution transmission electron microscopy, electron-energy-loss spectroscopy and in situ ellipsometry. It will be shown that c-BN films with high phase purity can be prepared at sufficiently strong ion bombardment as well as substrate temperatures above 160 degrees C. The c-BN phase was found to grow exclusively on top of the well-known hexagonal interlayer with c-axis orientation parallel to the substrate surface. Two types of nucleation were observed, the first characterized by c-BN (111) and the second by c-BN (001) lattice planes growing parallel to the (0002) lattice planes of the initially formed h-BN layer. c-BN films were prepared at maximum growth rates of 16 nm/min. Additional UV-photon irradiation of the growing films results in distinct modifications of the microstructure of the BN films. Using laser pulse energy densities on the substrate surface above 200 mJ/cm(2) the laser irradiation leads to the formation of turbostratic h-BN even though the unirradiated film regions of the same sample show the cubic structure. In contrast, films irradiated at 100 to 160 mJ/cm(2) are cubic. Electron microscopic observations show that in this range the mean diameter of crystallite in the excimer laser irradiated regions increased by a factor of two in comparison with unirradiated regions of the same sample. The experimental results will be discussed in context with the results of temperature field calculations. (C) 1999 Elsevier Science S.A. All rights reserved.