Growth processes of nanocrystalline diamond films in microwave cavity and distributed antenna array systems: A comparative study

The microwave discharges were investigated by plasma modelling in case of the BJ reactor and by optical emission spectroscopy (OES) in the visible spectral range and laser absorption spectroscopy in the mid-infrared spectral range (MIR-LAS) in the case of the DAA reactor in order to determine major and key species densities as well as the gas temperature nearby the substrate. The latter is considerably higher in the BJ reactor (around 2000 K) than in the DAA reactor (below 1000 K). Thus, the plasma kinetics are mainly driven by thermal chemistry in the BJ reactor, whereas both thermal and electron driven processes govern the plasma chemistry in the DAA reactor, which results in a significantly different plasma composition close to the substrate surface. The predominance of H, C and CO species, depending on the reactor type, the comparable amount of CH3 radicals, and the related impact on NCD growth are discussed, as well as the dissociation efficiency of both processes, with respect to the coupled microwave power.