Local growth studies of CVD diamond using a probe-like substrate

Diamond films produced by Ar/H₂/CH₄ RF induction plasmas have high growth rates but often lack uniformity across the substrate. In this paper, the diamond growth on a probe-like molybdenum substrate, 4.76 mm in diameter, is correlated with the location of the probe in the plasma flame. Optical emission spectroscopy is used to characterize the plasma during deposition. The differences in gas temperature and electron density between the central and the outer region of the flame, as well as the variations in heat flux to the substrate at the different positions, are well reflected in the formed deposit. It is shown that uniform growth can only be expected within the homogeneous core of the plasma. The paper also addresses the gas phase boundary layer above the growing film. Spatially resolved emission spectroscopy measurements of concentration evolution inside the boundary layer region are made possible by the small dimensions of the substrate. A decrease in thermal boundary layer thickness from approximately 4.5 to 3 mm induced by an increase in plasma power enhances the lateral growth of the individual diamond crystallites and improves surface coverage. The typical film thickness growth rate of 70 μm/h is, however, not seen to be affected