BIAS-ENHANCED NUCLEATION OF DIAMOND DURING MICROWAVE-ASSISTED CHEMICAL-VAPOR-DEPOSITION

Bias-enhanced chemical vapor deposition of diamond was investigated, u sing cross-sectional transmission electron microscopy and concurrent e lectron energy-loss spectroscopy to characterize the deposited materia l. Under the conditions investigated, the negative bias leads to the f ormation of a thin amorphous carbon layer. The growth rate of this lay er is relatively independent of the substrate temperature, which indic ates that amorphous carbon is formed by the deposition of positively c harged hydrocarbon or carbon ions. Reactive neutral species in the pla sma, 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 site s form as the amorphous layer is deposited. These sites are probably s mall clusters of either sp3 or sp2 carbon. Raman spectroscopy shows th at the material deposited under biased conditions is a mixture of sp3 and sp2 carbon, compared to the purer diamond that forms at the same t emperature, pressure, and gas composition when unbiased growth follows a biased pretreatment. Thus, while the deposition of energetic ions l eads to the creation of diamond nucleation sites, it also inhibits dia mond growth.