Effect of bias enhanced nucleation on the nucleation density of diamond in microwave plasma CVD

The variation of diamond nucleation density as a function of the conditions of bias enhanced nucleation (BEN) were studied. The nucleation density increased with microwave power, but decreased with the substrate temperature. The nucleation density also increased with bias voltage above 60 V, and had a maximum around 100 V. The crystal growth of diamond took place when either the bias voltage was high or the deposition time was long. The shift of C_1s energy measured by X-ray photoelectron spectroscopy indicated that the ratio of carbon sp³ bonds in the amorphous carbon and/or SiC phases formed before the nucleation of diamond, increased around the bias voltage of 100 V, which seemed to be the reason for enhancement of diamond nucleation by bias voltage. A simple computer simulation was performed in order to understand the effect of BEN conditions on the nucleation of diamond. The simulation reproduced the experimentally observed changes of nucleation density and particle size.