Optical diagnostics of microwave plasma in process of micro/nanocrystalline diamond deposition on hard alloy tools

Abstract

Diamond coatings on hard alloy tools produced by chemical vapor deposition (CVD) from methane-hydrogen mixtures greatly enhance the functional properties such as wear resistance and quality of the material processing. By varying the gas composition during the diamond film growth it is possible to cyclically change the film structure between microcrystalline diamond (MCD) and nanocrystalline diamond (NCD) to produce MCD/NCD multilayers that improves the mechanical properties of the film and reduces its stress and roughness. As the diamond growth occurs with participation of radicals generated in the plasma thermo-chemical reactions it is important to control in situ the presence of those species and gas temperature Tg. Here we used optical emission spectroscopy (OES) to monitor atomic hydrogen, CN, CH and C2 dimer radicals in course of deposition of MCD/NCD coatings by microwave plasma CVD in CH4-H2 and CH4-N2-H2 mixtures. The gas temperature has been calculated from analysis of rotational components of structure of C2(Δν = 0) emission line. We found that addition of nitrogen (4%) in CH4-H2 plasma, which is needed to form NCD, significantly, by about 500 K reduces Tg (from Tg = 3910 K to Tg = 3330 K). We developed an algorithm tolerable to small shifts of the measured spectral lines which provided fast calculation of Tg, so that the spectrum record and the automatic processing of fine structure of C2(Δν = 0) line totally take the time of about 5 min.