Depth resolved stress investigations of c-BN thin films

Cubic boron nitride thin films were deposited by ion beam assisted deposition (IBAD) on (100)-oriented silicon cantilever structures prepared by standard micro-machining processes. This enables an accurate determination of the stress-induced bending of the beam by optical microscopy. Depth resolved characterisation of the coatings was achieved by subsequent back-etching and examination of the film stress and the IR data after each sputtering step. Cubic BN containing films exhibit a three layer sequence: non-cubic baselayer/transition h-BN --> c-BN/c-BN toplayer. This layered sequence was verified by the evolution of the IR data as well as the stress distribution. These investigations confirm the existence of a transition region between the h-BN baselayer and the c-BN toplayer. Furthermore, the dependence of the depth-resolved c-BN stress sigma (c-BN) on the main deposition parameters was investigated. A stress reduction can be achieved by reducing the Ar/N-2 ratio and/or by increasing the ion energy. As this stress relief is correlated with an increase of the Sp(2) bonded material within the c-BN toplayer, it can be concluded that stress relaxation occurs at the sp(2) bonded grain boundary material. Finally, the influence of the stress on the nucleation and the growth of c-BN containing films will be discussed. (C) 2001 Elsevier Science B.V. All rights reserved.