Crystallography and structural evolution of cubic boron nitride films during bias sputter deposition

The mechanism and the crystallography of the growth of cubic boron nitride (c-BN) films deposited on [100]-oriented silicon substrates by radio-freque ncy bias sputtering have been studied by means of cross-sectional high-reso lution transmission electron microscopy. Particular attention has been paid to the atomic structure of graphitic (sp(2)-bonded) BN and grain boundarie s in the c-BN films. The c-BN films grow in the sequence of amorphous boron nitride (a-BN), turbostratic boron nitride (t-BN) and c-BN layers, similar to previous results. The sp(2)-bonded BN material consists of small region s, 1-5 nm thick, forming in a layered manner parallel to the substrate surf ace. Each region consists of parallel lamellae in both the hexagonal and rh ombohedral (h-BN and r-BN, respectively) configurations. Three orientation relationships between h-BN and r-BN phases were determined: OR-1: [2<(11)ov er bar>0](h-BN)parallel to[2<(11)over bar>0](r-BN) (0001)(h.BN)parallel to( 0001)(r.BN); OR-2: [2<(11)over bar>0](h). (BN)parallel to[2<(11)over bar>0] (r-BN), (01 (1) over bar 0)(h-BN)parallel to(01<(11)over bar>)(r-BN); OR-3: [2<(11)over bar>0](h-BN),parallel to[2<(11)over bar>0](r-BN). (01 (1) over bar 0)(h-BN)parallel to(01 (1) over bar 2)(r-BN). The r-BN crystallites wi thin the sp(2)-bonded BN grow preferentially in such a way that the (01 (1) over bar 2)(r-BN)parallel to(01<(11)over bar>)(r-BN) plane is almost paral lel to the grain boundary. Twinning about both the basal planes and the {01 (1) over bar 1}(r-BN) planes is common within r-BN phase. The c-BN crystal lites adjacent to the graphitic BN layer are highly twinned, the {111}(c-BN ) twin planes being parallel to the basal planes of the sp(2)-bonded BN. Th e c-BN phase nucleates on the oriented graphitic BN layer in a semicoherent manner and obeys specific orientation relationships with the hexagonal and rhombohedral phases, namely: OR-I: [(2) over bar 110](r-BN)parallel to[110](c-BN) OR-II: [(2) over bar 1 10](r-BN)parallel to[<(11)over bar>0](c-BN) (01<(11)over bar>)(r-BN)parallel to((1) over bar 11)(c-BN ()interface plane ) (01 (1) over bar 2)(r-BN)parallel to(1<(11)over bar>(c-BN) (interface pla ne) (0001)(r-BN)approximate to parallel to(1 (1) over bar 1)(c-BN) (0001)r-BN(a pproximate to)parallel to(1 (1) over bar 1)(c-BN) They are related by a rotation of 180 degrees about their common axis, [000 1](r-BN)parallel to[1 (1) over bar 1](c-BN) [2<(11)over bar>(h-BN)parallel to[110](c-BN)] (01 (1) over bar 2)(h-BN)parallel to(001)(c-BN) (0001)(h-BN)parallel to(1 (1) over bar 1)(c-BN) In the mainly c-BN region of the films, twins are present about more than o ne of the sets of {111}(c-BN) planes. The intrinsic microstructure of the c -BN films and the crystallography between the cubic and graphitic BN phases show that the structure of cubic boron nitride is directly related to the structure of the precursor phases. The atomic structure of an interface dep ends on the orientation relationship between adjacent c-BN grains and the b oundary inclination. The grain boundaries consist of twin boundaries when t wo adjacent grains are oriented close to the [110],.,, zone axis and the bo undary plane is parallel to the {111}(c-BN) close- packed planes of both gr ains. However, a thin layer, 1-2 nm, of sp(2)-bonded BN forms between the c -SN grains when the boundary plane inclines a few degrees from the (111)(c- BN), planes of the adjacent grains. (C) 2000 Acta Metallurgica Inc. Publish ed by Elsevier Science Ltd. All rights reserved.