Oriented CVD diamond films - twin formation, structure and morphology.

We studied three types of oriented diamond film: (I) strongly fibre textured films, (II) epitaxially textured films grown on (100) Si, and (III) homoepitaxial films. The samples were prepared using microwave plasma assisted chemical vapour deposition from CH4-H2 gas mixtures under various growth conditions. In all cases the structure and morphology of the films are shown to depend on the growth parameter alpha which is given by the relative growth rates on (100) and (111) facets, alpha=(V100/V111) square root of 3. In the case of fibre textured diamond films, the crystallographic direction of the fibre axis is correlated directly with alpha which in turn depends on the growth conditions. Based on the X-ray analysis of a variety of samples, a diagram is established showing the dependence of alpha on the methane concentration and on the deposition temperature. The structure and morphology of the films are strongly affected by twin formation. In the case of homoepitaxial or heteroepitaxia lly textured diamond films, the susceptibility to twin formation depends critically on alpha. For (100) oriented films large values of alpha (e.g. alpha nearly 2,5) result in a suppression of twin formation, whereas low values of alpha (e.g. alpha nearly 1,5) lead to a deterioration in the film orientation and morphology due to twinning. To elucidate the influence of alpha on the formation of twins, the evolution of crystal shapes and structures was simulated numerically. These simulations provide clear explanations for a number of experimental findings.