Morphology and Structure of cBN Films

Up to now, most work on cBN deposition has been done using single crystal silicon substrates. Those films grow in a typical phase sequence which has been shown for the first time by Kester et al. [37] in 1993 and since then confirmed by many groups At first an amorphous layer at the interface to the substrate is formed which is usually referred to as aBN. This layer probably contains also some silicon from the substrate and is due to ion-induced intermixing. After that a turbostratic boron nitride (tBN) layer is formed. Turbostratic boron nitride is a BN form consisting of nearly parallel hBN-like layers which, however, do not have defined three-dimensional orientation. The distance of these layers is a few percent enlarged in comparison to the hBN crystal (see e.g. [1]). Under deposition conditions which 

5 Vapor Phase Deposition of Cubic Boron Nitride Films 

The cBN films are polycrystalline with columnar grains about 10-20 nm in diameter extended perpendicular to the surface. 

The cBN crystallites have a preferential orientation. Some authors report on a (110) texture [38,39], others [40] found a so-called double-fiber texture. Both textures are characterized by an alignment of 111 planes perpendicular to the surface. The difference is that in the case of the (110) texture the (111) planes have a preferred azimuthal orientation (i.e. the (110) direction is parallel to the substrate normal), whereas in the case of the double-fiber texture the orientation about the in-plane [111] axis is random. However, both textures do support the suggestion that the structural transition from hBN to cBN growth is characterized by three (111) spaces of cBN (cfni = 0.209 nm) matching two (0002) spaces of tBN 

A necessary condition for cBN phase formation in thin films is that boron and nitrogen are incorporated in a nearly 1 1-ratio. Based on highly accurate composition measurement using neutron depth profiling, Hackenberger et al. [41] investigated the relationship between film stoichiometry and the phases present in the film. From these measurements, together with an analysis of data from the literature, they found evidence that film stoichiometry is one of the factors that stabilize the cubic phase. 

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