Growth and defects of diamond facets under negative biasing conditions in a microwave plasma CVD process

The influence of an additionally applied bias voltage on the growth mode of individual crystal facets during the microwave plasma chemical vapour deposition (MPCVD) of diamond films has been studied for bias voltages varying between -50 and - 200 V. The facet morphology was characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Information about the deposited carbon phases was deduced from transmission electron microscopy (TEM). For the originally flat {100} facets a roughening is observed showing a completely different behaviour as a function of the applied bias voltage. A bias voltage of -50 V does not disturb the homoepitaxial diamond growth. At - 100 V the individual {001} facets start to split with the coherently growing domains, initially being bordered by [100], [010] or [110], [110] edges. For longer exposure times the observed morphology points to an increase of the growth rate on the top {001} Facets as compared with that on the corresponding {111} planes, which may formally be described in terms of a growth parameter a>3 and an additional instability of the (001) facets causing the splitting. In contrast, at -200 V the growth mode changes completely. Bulb-like structures consisting of nanocrystalline diamond and amorphous carbon nucleate at the edges of the {100} facets and successively overgrow the whole surface. The orientation is rapidly lost. (C) 1997 Elsevier Science S.A.