Optical and mass spectroscopic properties of microwave CH4/H2/Ar plasma for diamond deposition in a resonance cavity

The properties of microwave CH4/H2/Ar plasma for diamond deposition in a resonant cavity have been investigated by optical emission spectroscopy (OES) and quadrupole mass spectroscopy (QMS). Ar emission intensity decreases monotonically with gas pressure, where electron impact excitation plays an important role. Hα. CH and C2 intensities exhibit the different pressure dependences, which decrease at first and then rise with the further increasing of gas pressure, suggesting the change of electron activation mechanism to thermally driven chemistry for the formation of excited reactive hydrocarbon species at high gas pressures. The addition of small amounts of CH4 to the H2/Ar plasma causes increases in emissions of Hα and CH generated from the CH4 dissociation. With further increase of CH4 flow rate, both emissions and abundances of 2-carbon species enhance, while a reduced intensity of CH emission is observed, reflecting the complex dissociation and dimerization reactions of hydrocarbon species. The dissociation of CH4 is enhanced in plasma under higher power condition. A slight change can be observed in both emission and abundance of hydrocarbon species with increasing Ar flow rate.