Due to the attractive properties, diamond-like amorphous carbon (DLC) films have been developed as resist material for photo lithography and as hard coatings. For these applications flat surfaces are required. In this work, the surface morphology and the deposition mechanism of DLC films have been investigated. Using parallel plate r.f. plasma glow discharge, methane gas was decomposed for deposition of DLC films on the third electrode located perpendicularly to the two parallel plates. The DLC films were deposited on Si substrates at various distances from the plasma discharge and different bias voltages. IR spectra of the DLC films were taken with an FTIR spectrometer. Determination of the roughness was performed by atomic force microscopy (AFM). An optical emission profile taken between plasma edge and substrate surface was employed to monitor the occurrence of neutral radicals.
The roughness of the DLC films strongly depends on the bias voltages, because the voltage influences the acceleration energy of ionic species hitting the substrate surface. Furthermore, the roughness of the samples depends on the distance between the substrate and the plasma discharge. Characteristically, the roughness decreases with distance up to 20 mm after which it increases again. From the result, the ratio of neutral and ionic species was concluded to be very important for the flatness of the DLC films. In order to fabricate flat DLC films, it is very important to control the energy of ionic species and the ratio between ionic species and neutral radicals.