Properties of cubic boron nitride films with buffer layer control for stress relaxation using ion-beam-assisted deposition

Significant ion irradiation during film growth is required for the formatio n of cubic boron nitride (cBN) films. Meanwhile, a huge level of intrinsic stress possibly induced by the ion bombardment has been frequently reported to result in cracking and/or lack of adhesion of deposited cBN films. The present work has been performed to investigate the interfacial and/or the b uffer layer structures with better matching to the cBN film by relaxation o f the film stress using ion-beam-assisted deposition (IBAD). Boron nitride films have been synthesized on Si(100) wafer and tungsten carbide (WC) subs trates by depositing boron vapor under simultaneous bombardment with nitrog en ions and nitrogen-argon mixture ions in the energy range of 0.5-10 keV. Cubic BN films with enhanced tribological properties have been explored by inserting a BN layer with various B/N compositions as a controlled buffer a t the interface. Significant relaxation of the film stress has been observe d for the buffer layer with a boron-rich (B-rich) composition (B/N similar to 10) with hardness maintained at a relatively high value (similar to 30 G Pa). A structural analysis by Fourier transform infra-red spectroscopy (FTI R) and cross-sectional transmission electron microscopy (TEM) confirms that polycrystalline films with a high cBN fraction were synthesized on the B-r ich layer. Formation of the cBN films with a B-rich buffer layer enabled th e tribological characterizations to be performed, and the tribological prop erties have been observed to be significantly enhanced with the insertion o f the B-rich buffer and the enhancement of atomic intermixing at the initia l stage of cBN layer growth. Using the nanoindentation method, the hardness of the cBN films with a high cubic fraction was found to be as high as the values for the bulk cBN. (C) 1999 Elsevier Science S.A. All rights reserve d.