MECHANISMS OF DIAMOND FILMS DEPOSITION FROM MPACVD IN METHANE-HYDROGEN AND NITROGEN MIXTURES

The addition of nitrogen to the CH4-H-2 gas mixture used for diamond g rowth by microwave plasma assisted chemical vapour deposition (MPACVD) strongly modifies the plasma reactivity and thus the deposition rate, the structure, and the physical properties of the films. It has been pointed out that nitrogen reduces the relative concentration of carbon deposition precursors such as CH and strongly enhances the etching pr ocess. When a diamond film is present in the centre of the plasma, a r elatively high CN concentration could be detected in the discharge eve n after closing the gas line introducing methane in the gas flow. This can be considered as evidence of the etching of the diamond film by t he plasma, resulting in the formation of CN radicals. The effect of ni trogen on the structure and quality of diamond films is discussed from the results of scanning electron microscopy and Raman spectroscopy. ( C) 1998 Elsevier Science S.A.