Removal of sp2-boron nitride transition layer in the growth of cubic boron nitride films

Practical application of cubic boron nitride (cBN) films is known to be hindered by its bad adhesion to substrates. One reason is that an sp2-bonded boron nitride (sp2-BN) transition layer is formed on the substrate surface at the early stage of deposition prior to the nucleation of cBN, which weakens the link between the cBN-rich layer and the substrate. In this study, we demonstrated the feasibility of removing this sp2-BN layer, by replacing it with a zirconium- (Zr-) rich composite layer. The method is to deposit a multilayer of Zr layer/sp2-BN layer/cBN-rich layer at 680 °C on a tungsten carbide substrate, followed by annealing the structure at 850 °C for 1 h. X-ray photoelectron spectroscopy, transmission electron microscopy and electron energy loss spectroscopy analyses showed that the Zr metal layer and sp2-BN layer reacted completely, to produce a composite interfacial layer consisting of metal Zr, Zr nitride, boride and oxide. The depth profiles of the elemental distributions and chemical states were investigated and discussed to reveal the diffusion of the elements associated with this deposition process.