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

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 CH4-H2 mixtures at pressure of 320 Torr and MWPD of ~700 W/cm3 even at relatively low (3%) CH4 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 C2 dimer) were characterized with spatially resolved optical emission spectroscopy (OES) at moderate and high MWPD. The maximum rotational gas temperature Tg significantly enhanced to 3700 K in the latter case (675 W/cm3) compared with Tg ≈ 3100 K for lower pressure and MWPD (100 Torr, 160 W/cm3), 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.