Investigation of the nucleation of c-BN by AFM measurements

The poor adhesion commonly observed for c-BN thin films is caused by the high compressive stress of the films and the low adhesion strength at the interface. In general, the adhesion strength of a coating is determined by the nature of its interface to the substrate and, therefore, influenced by the nucleation process. In order to evaluate the mechanisms of c-BN nucleation a nucleation sequence was deposited by inductively coupled plasma CVD (ICP-CVD) and investigated by AFM measurements. The surface roughness of all films is rather high and increases with deposition time. The height differences within the films are also rather large. The AFM images show small rounded features at the surface, which become more and more prominent with deposition time. It is speculated that they are the first c-BN nanocrystals formed on a h-BN nucleation layer. Finally, our results will be discussed in view of the growth mode of the nucleation layer, which can be correlated with the delamination behavior of the c-BN films.