Optical emission spectroscopic studies of microwave enhanced diamond CVD using CH4/CO2 plasmas

Diamond films have been grown using CH4/CO2 gas mixtures in a microwave pla sma deposition reactor. Optimum growth of well-faceted polycrystalline diam ond occurs at approximately 50% CO2/50% CH4 with a growth rate of approxima tely 1 mu m h(-1) for a process pressure of 45 Torr and 1 kW applied power. Optical emission spectroscopic studies of CH4/CO2 microwave plasmas have b een performed for a range of different process conditions, and the results correlated with diamond film quality and growth rate. Emission spectra (300 -800 nm) are presented for gas compositions ranging from 100% CO2 to 100% C H4. Spectral peaks from electronically excited C-2, C-3, CH, CO, O and H ha ve been observed, and maxima in the ratios of the CH:C-2, CH:C-3 and H:C-2 emission intensities are all found to correlate with process conditions for good quality diamond. By assuming that the rising spectral background at l ong wavelength can be attributed to blackbody radiation from macroscopic ca rbonaceous particles, we estimate the average gas temperature of the plasma to be: 1925 K. For 100% CO2 plasmas, emission peaks from atomic Mo are obs erved, indicating etching of the Mo substrate holder. (C) 2000 Elsevier Sci ence S.A. All rights reserved.