Deposition of c-BN by ion beam assisted CVD

The main problem in growing c-BN rich films in the past has been their very high intrinsic stress, leading to partial or complete detachment from the substrate after reaching a critical thickness of 200 nm. The process we are using is closely related to IBAD or IAE. However. in addition to the evapo ration of boron atoms and simultaneous nitrogen ion bombardment by an ion g un, the films were grown in a highly reactive gas (SF6, BF3) atmosphere, pr ovided by a nozzle close to the Si substrate [chemically modified ion assis ted evaporation (CMIAE)]. Reactive gases were used to verify preferential e tching of impurities and different phases of boron nitride. SF6 represents a pure etchant. BF3, in addition, is a boron source. With this modification it was possible to grow films at 450 degrees C with a c-BN content of 85% up to a thickness of 800 nm. The films showed very go od adhesion and could be deposited over a wide range of ion/neutral (I/N) r atios (0.4-1.2), depending on gas flux and geometrical condition. Furthermo re, c-BN films could also be grown at much lower temperatures down to 120 d egrees C. The analysis of the films was performed by IR and AES spectroscopy. The fil m thickness was measured independently by Talystep and Dektak. Although the details of the mechanism are not yet understood, the reactive gas assistan ce is very promising for obtaining rather thick films with high c-BN conten t and good adhesion. Further experiments on CMIAE deposition on iron and st eel substrates are in preparation. (C) 2000 Elsevier Science S.A. All right s reserved.