Kinetics of the initial stages of CVD diamond growth on non-diamond substrates: Surface catalytic effects and homoepitaxy

Recently, we have reported that the density of chemical vapour deposition (CVD) diamond particles obtained on non-diamond substrates abraded with a diamond slurry can be enhanced by a few orders of magnitude by abrasion with a mixed metal/diamond slurry. In this work, we present growth kinetics studies of isolated diamond crystallites (prior to coalescence into a continuous film), which are formed at the initial stages of deposition on metal/diamond and diamond-pretreated silicon. The metals used were Ti, Fe and Cu. It has been found that the temperature dependence of the diamond growth rates on differently pretreated substrates can be described by an Arrhenius plot. From these plots, it has been concluded that at the initial stages of deposition the activation energy for CVD diamond formation, as observed for diamond-abraded substrates, can be substantially decreased as a result of substrate surface pretreatment with a mixed metal/diamond slurry. However, after coalescence of the crystallites into a continuous film, the activation energies for metal/diamond and diamond-pretreated substrates were found to be similar. Based on micro-Raman measurements it has been found that at the initial stages of deposition, the quality of diamond that was grown on the metal/diamond abraded substrates is higher than that deposited on the diamond-abraded ones. In contrast, after a long deposition time, the quality of diamond grown on the differently pretreated substrates was found to be similar. It is suggested that the observed effects are associated with the metal's catalytic activity towards the hydrogenation of unsaturated hydrocarbons, namely enhancing the concentration of sp(3)-bonded hydrocarbon fragments. At the initial stage of deposition, before a stable substrate is formed, this enhancement leads to an increase in the diamond growth rate, lowering of the activation energy for its homoepitaxial growth on diamond residues left by pretreatment, and improvement of its quality. (C) 1997 Elsevier Science S.A.