Improvement of nanocrystalline diamond film growth process using pulsed Ar/H2/CH4 microwave discharges.

For the first time nanocrystalline diamond (NCD) films were deposited by the pulsed microwave plasma assisted chemical vapour deposition process starting from an Ar/H₂/CH₄ gas mixture. Comparisons with continuous mode deposition gave evidence for the improvement in film quality when the microwave power was modulated with a pulse repetition rate in the range 50–1000 Hz. A reduction in grain size and surface roughness, especially at low pulse repetition rate, accompanied by a decrease in soot particle formation was observed. A thermo-chemical plasma model, developed for pulsed Ar/H₂/CH₄ microwave discharges, provides evidence for the fact that the pulsed mode permits the enhancement of the mole fraction of the C₂ dimer assumed to be the growth precursor of NCD. This may be responsible for a high secondary nucleation rate improving the nanostructure of the film in pulsed discharges. [ABSTRACT FROM AUTHOR]