Microwave plasma-assisted chemical vapor deposition of microcrystalline diamond films via graphite etching under different hydrogen flow rates

Diamond films on Si substrates were synthesized in a chemical vapor deposition (CVD) reactor with graphite plates as the carbon source, which were etched using hydrogen plasma. The effect of the hydrogen flow rate (13 to 200 sccm) on the diamond growth rate, morphology, and quality was investigated. While only nanocrystalline diamond was produced at the lowest flow rate of 13 sccm, microcrystalline diamond films were grown at a higher H₂ flow rate, whose growth rate increased from 1.7 μm h⁻¹ to ∼5 μm h⁻¹ with the hydrogen flow rate decreasing from 200 sccm to 25 sccm, but at the expense of quality. The structure degradation of the films was quantified with Raman spectroscopy and XPS analysis. These results are ascribed to an increase of abundance of the produced hydrocarbon radicals, such as C₂ and CH with reduced hydrogen flow rates, as deduced from the optical emission spectra of the plasma in the course of graphite-etching/diamond-deposition.