The chemical nature of the carbon precursor in bias-enhanced nucleation of CVD diamond

The effect of sample biasing on CVD diamond nucleation on Si(100) substrates by the MW method has been previously addressed; however, the question as to the changes a silicon substrate undergoes under bias treatment is still open. In the present work we address this question by investigating the chemical reactivity of the material deposited during substrate bias. The different etching behavior in a hydrogen plasma of the possible precursor layer formed on silicon during the bias treatment is utilized. Silicon substrates were subjected to a three-step sequential process: (i) bias pretreatment, (ii) exposure to a pure hydrogen plasma and (iii) deposition under the normal conditions. The characterization of the deposited films following each of these stages was carried out by Raman, AES and AFM. It was found that the carbon precursor to diamond growth, formed during the biasing stage, is stable under the etching process. This result suggests that the deposited material al this stage does not consist solely of a carbon network etchable by the hydrogen plasma, such as amorphous carbon (sp(2) or sp(3) bonded and microcrystalline graphite or silicon carbide. It may therefore, be suggested that the precursor to diamond growth deposited during the bias process consists of non-etchable nanocrystallite diamond particles. (C) 1997 Elsevier Science S.A.