INVESTIGATION OF THE NUCLEATION LAYER IN C-BN FILM GROWTH

The nucleation of c-BN during an inductively coupled plasma chemical v apour deposition (CVD) process is investigated. The transition from th e textured h-BN nucleation layer to the c-BN layer turned out to be no t abrupt but to take place rather gradually in several steps. Increasi ng the substrate temperature sharpens the transition and increases the maximum c-BN content. It is speculated that this is correlated with a decreasing hydrogen content of the films at higher temperatures. Expe riments with different bias voltages during the nucleation step reveal ed that c-BN nucleation is possible only within the well-known c-BN re gion of the parameter space. Thus, this region might be determined by the nucleation of c-BN rather than by the growth step. Experiments wit h boron-rich interlayers finally results in extremely high c-BN conten ts of the subsequent c-BN layers. (C) 1997 Elsevier Science S.A.