HETEROGENEOUS CHEMICAL EFFECTS IN THE DEPOSITION OF CVD DIAMOND

In this work, diamond has been deposited by the HF-CVD (Hot Filament C hemical Vapour Deposition) method on Si and Ti substrates and on diffe rent aggregate states of the two components. All substrates have been abraded with diamond slurry prior to deposition. Ti has been incorpora ted onto Si substrates as small particles by adding Ti powder to the a brading slurry, or by evaporation of thin Ti layers of different thick ness. By inducing these chemical and morphological modifications to th e surface, we aimed to investigate the effect of the aggregate state o f titanium on the initial stages of deposition. Micro-Raman measuremen ts show that the diamond crystallites grown on diamond abraded silicon are of high quality. However, in the presence of Ti, an enhanced form ation of graphite alongside diamond particles is observed. The density of deposited diamond particles on the various substrates has been inv estigated by AFM (Atomic Force Microscopy) and SEM (Scanning Electron Microscopy), and has been found to follow the order: Si abraded with D i and covered by Ti films < silicon abraded with Di < Si abraded with Di + Ti approximate to Titanium substrates abraded with Di. The interf ace between the Si substrate and the deposited diamond at the initial stages of deposition has been studied by means of FTIR spectroscopy. I n the presence of Ti, more SiC has been formed relative to samples abr aded with Di slurry solely. It is suggested that the observed enhancem ent in diamond particle density may be related to a more efficient ent rapment of carbonaceous fragments by Ti-containing surfaces than by th e Si ones, leading to an accelerated process of diamond formation at t he initial stages of deposition. It is concluded that the presence of diamond debris is an obligatory condition for diamond growth, and that Ti enhances diamond formation efficiently only if diamond debris is e xposed to the gas phase. (C) 1998 Elsevier Science S.A.