Quantitative study of epitaxial CVD diamond deposits: Correlations between nucleation parameters and experimental conditions

In the case of diamond deposit obtained by microwave plasma assisted chemical vapour deposition technique (MPCVD) where the bias enhanced nucleation (BEN) was used to initiate diamond islands on silicon substrate, we simultaneously studied nucleation parameters such as crystal density and epitaxial ratio according to main synthesis conditions. These ones were relative to in situ pretreatment steps occurring before diamond growth, i.e. plasma etching and bias sequences. The nucleation parameters were studied by the high resolution SEM associated to image analysis techniques on homogeneous 1 cm2 samples.We observed that hydrogen etching duration clearly modified the epitaxial ratio without any change on the crystal density. So an optimal epitaxial ratio was reached for a moderate hydrogen etching while crystal density remained quite constant. The bias step was analysed in terms of duration and electrical behaviour (voltage and intensity) in relation to the plasma density that we were able to modify by physically confining the discharge. Bias duration clearly modified crystal density and epitaxial ratio. In later case, we observed a short optimal duration (between 30–90 s) for a 120 V bias voltage depending on the etching. We showed too that for a given bias duration the epitaxial ratio was all the more high as the voltage is low. The study of crystal density in relation to electrical characteristics of bias step showed that the more important parameter for nucleation is the electrical charge density (including intensity and time) and not the voltage, since nucleation density of 108 cm− 2 can be maintained for voltage close to 35 and 50 V respectively if the plasma power density during the bias is higher or if the BEN duration is longer.