NUCLEATION MECHANISMS OF DIAMOND IN PLASMA CHEMICAL-VAPOR-DEPOSITION

In a recent paper, we reported that a density of diamond nuclei as high as 10(10) cm-2 was attained on a mirror-polished silicon surface by pretreating the substrate surface in a hydrogen plasma containing a high concentration of methane and applying a negative bias. Under the most suitable conditions giving the highest density of diamond nuclei, i.e. pretreatment in hydrogen plasma with a methane content of 40% at a bias voltage of -100 V for 5 min, the obtained growth product was of star-ball shape consisting of amorphous carbon, silicon carbide and diamond. Amorphous carbon was found to be easily etched by the hydrogen plasma in the early stage of diamond growth after the pretreatment. Based on the above results. we present a model suggesting the mechanisms for the enhancement of diamond nucleation. The application of a negative bias collects carbon ions at higher rates onto the silicon surface, and increases their bond strength with the surface silicon owing to ion mixing. This enhances the formation of carbon clusters, overcoming re-evaporation and diffusion. The impinging energetic ions destroy the weak sp2 structure and increase the sp3 structure, leading to the formation of diamond nuclei precursors.