Formation of c-BN thin films under reduced ion impact

A special multistep r.f. magnetron sputtering process with an h-BN target was investigated. After proper pretreatment a very thin c-BN film was grown under optimum conditions. For further film deposition the gas atmosphere was changed to pure nitrogen and the substrate bias voltage was reduced. Using Langmuir probe measurements we analyzed the ion flux towards the growing film and found that the strength of the ion impact sufficient to maintain c-BN growth is much smaller than that necessary to initiate the growth of c-BN. This has been demonstrated in terms of the total incorporated momentum per deposited atom as well as considering ion energy and ion-to-atom flux ratio. We conclude that continuation of c-BN growth after the formation of a certain initial c-BN layer is governed by an epitaxial mechanism. (C) 1997 Elsevier Science S.A.