Express in situ measurement of epitaxial CVD diamond film growth kinetics

We used a low-coherence interferometry for precise continuous in situ measurements of thickness and growth rate of epitaxial single crystal diamond layers in microwave plasma CVD in H-2-CH4 gas mixtures in a broad range of substrate temperatures T-s (750-1150 degrees C) and CH4 concentrations (1-13%). Rich growth kinetics is collected in a single experiment by depositing about 60 layers on one (100) lb HPHT diamond substrate in different regimes (the substrate temperature was controlled by the microwave power) at fixed pressure P = 130 Torr, without the plasma switch-off. The growth rate is found to follow Arrhenius dependence with activation energy E-a = 11.1 +/- 1.0 kcal/mol. By appropriate choice of the substrate temperature the growth rate can be significantly enhanced. The growth rate as high as 82 mu m/h is achieved by optimizing the temperature and gas composition. At low CH4 content (1%) growth competes with etching by atomic hydrogen, the etching dominating at high T-s (>1000 degrees C in the present conditions). The etching rate in pure H-2 plasma was measured and activation energy E-a = 9.8 +/- 0.8 kcal/mol was deduced. Gas temperature T-g in the plasma core evaluated from optical emission spectra for dimer C-2 (Swan band), was found to be either constant or slightly and monotonically increasing with absorbed power, whereas the absorbed microWave power density shows a decreasing, although slight, trend. This suggests the temperature depended surface reactions to play a major role in the diamond growth kinetics under variable microwave power. Raman mapping of cross-section of the produced mukilayered sample confirmed high quality of diamond structure over all the deposition regimes explored. (C) 2017 Elsevier B.V. All rights reserved.