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 mo de of individual crystal facets during the microwave plasma chemical v apour deposition (MPCVD) of diamond films has been studied for bias vo ltages varying between -50 and - 200 V. The facet morphology was chara cterized by atomic force microscopy (AFM) and scanning electron micros copy (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 be haviour 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 do mains, initially being bordered by [100], [010] or [110], [110] edges. For longer exposure times the observed morphology points to an increa se of the growth rate on the top {001} Facets as compared with that on the corresponding {111} planes, which may formally be described in te rms of a growth parameter a>3 and an additional instability of the (00 1) facets causing the splitting. In contrast, at -200 V the growth mod e changes completely. Bulb-like structures consisting of nanocrystalli ne diamond and amorphous carbon nucleate at the edges of the {100} fac ets and successively overgrow the whole surface. The orientation is ra pidly lost. (C) 1997 Elsevier Science S.A.