Enhanced deposition rate of polycrystalline CVD diamond at high microwave power densities

Abstract We report on growth of polycrystalline diamond (PCD) by chemical vapor deposition (CVD) in a microwave plasma reactor under high absorbed microwave power density (MWPD) and high pressures, in conditions more typical for single crystal diamond epitaxy. The growth rates as high as 30–36 μm/h have been achieved in CH 4 -H 2 mixtures at pressure of 320 Torr and MWPD of ~700 W/cm 3 even at relatively low (3%) CH 4 concentration, using PCD substrates with diameter of 5–20 mm and different textures. The structure and quality of the produced PCD thick films were assessed with SEM, Raman and X-ray diffraction. The plasma shapes and spatial profiles of species (excited atomic hydrogen and C 2 dimer) were characterized with spatially resolved optical emission spectroscopy (OES) at moderate and high MWPD. The maximum rotational gas temperature T g significantly enhanced to 3700 K in the latter case (675 W/cm 3 ) compared with T g  ≈ 3100 K for lower pressure and MWPD (100 Torr, 160 W/cm 3 ), being in agreement with the obtained high growth rates at high pressures. Analysis of numerous literature data on PCD growth rate vs substrate size in MPCVD reactors reveals a clear trend of enhanced growth rate with diminishing of the substrate dimension, our findings further confirming this tendency indirectly related to a change in absorbed power density.