Bias-enhanced nucleation of diamond during microwave-assisted chemical vapor deposition

Abstract

Bias-enhanced chemical vapor deposition of diamond was investigated, using cross-sectional transmission electron microscopy and concurrent electron energy-loss spectroscopy to characterize the deposited material. Under the conditions investigated, the negative bias leads to the formation of a thin amorphous carbon layer. The growth rate of this layer is relatively independent of the substrate temperature, which indicates that amorphous carbon is formed by the deposition of positively charged hydrocarbon or carbon ions. Reactive neutral species in the plasma, particularly atomic hydrogen, are also believed to play a role in creating nucleation sites. Higher nucleation densities were observed after longer biased pretreatments, which suggests that nucleation sites form as the amorphous layer is deposited. These sites are probably small clusters of either sp3 or sp2 carbon. Raman spectroscopy shows that the material deposited under biased conditions is a mixture of sp3 and sp2 carbon, compared to the purer diamond that forms at the same temperature, pressure, and gas composition when unbiased growth follows a biased pretreatment. Thus, while the deposition of energetic ions leads to the creation of diamond nucleation sites, it also inhibits diamond growth.