REACTIVE ION ETCHING OF DIAMOND AND DIAMOND-LIKE CARBON-FILMS

Thin films of polycrystalline diamond and hydrogenated amorphous carbon were exposed to CF, SF6, and O2 plasmas. Their microstructures were observed by scanning electron microscopy (SEM), the surface was analysed by X-ray photo electron spectroscopy (XPS) and, in the case of the diamond thin films, the chemical quality and the roughness were estimated respectively by Raman spectroscopy and atomic force microscopy (AFM) measurements. The plasma phase and the etching products were analysed by on-line mass spectrometry. Different plasma conditions were used and the surface modifications induced were correlated with the chemical nature of the films. It was found that the fluorination of a-C: H films induces the formation on the surface of C-CF, CF, CF2 and CF3 bonds, whereas only CF bonds were observed on diamond films. Likewise, C=O and C-O bonds appeared, after O2 plasma exposure, on amorphous carbon while only C-O was detected on diamond surfaces. This was correlated with the amount of bonded hydrogen in the films and with their structure. Both types of film are etched in oxygen even if the mass spectrometry results are notably different. The etching of diamond films in SF6 is very slow whereas CF4 is clearly detected in the plasma in the case of a-C:H films.