HFCVD diamond grown with added nitrogen: film characterization and gas-phase composition studies

Recently there has been considerable interest in the addition of nitrogen to precursor gas mixtures and its influence on the properties of the resulting diamond films. Careful control of the nitrogen concentration in the CVD process results in changes to both the film growth rate and morphology. In addition to the well-defined and precisely controlled deposition conditions, thorough characterization of the vapour-grown material is indispensable in order to tailor diamond film properties according to specific applications. High quality diamond films have been produced via hot filament CVD (HFCVD) using a precursor gas mixture of 1% methane in hydrogen with N-2 additions varying from 50 to 5000 ppm (N/C 0.01-1.0). We report the results from both the structural and compositional characterization of the as-deposited HFCVD diamond films by scanning electron microscopy, Raman spectroscopy and X-ray diffraction. Both the diamond phase purity and growth rate are maximized with 200 ppm N-2 in the gas mixture with further additions resulting in reduced growth rates and poorer film quality. We explain these findings in terms of the concentrations of gas phase species obtained from chemical equilibrium calculations and in particular the importance of the CN radical to the diamond growth process. (C) 1998 Elsevier Science S.A.