Plasma Polymerization of Fluorocarbon Thin Films on Glass and Metal Substrates

Plasma polymerization of thin, fluorocarbon films onto glass, low carbon steel, and aluminium foil substrates using a hexafluoroethane (C2F6) glow discharge in a parallel plate, rf-sputter system was studied. Continuous, 100 nm thick fluoropolymer films were obtained when a graphite sputter target was used as the cathode material. Depositions conducted without the use of a consumable cathode produce continuous but thin (<10 nm) films of fluorocarbon material. Analysis of the plasma by optical emission spectroscopy determined that the dominant species in the discharge was CF2 for both target configurations. An increase in the intensity of specific CF2 transitions was observed when the graphite target was used. Characterization of the deposited films by X-ray photoelectron spectroscopy of the C 1s and F 1s photoelectrons was used to determine the atomic F/C ratio and distribution of CF3, CF2, CF, C-CF, and C binding states. Films fabricated with the graphite target had a lower F/C ratio than depositions made without a consumable target. However, the distribution of binding states and the F/C ratio in the fluoropolymer was dependent on the substrate material. The results of the study indicate that the fluoropolymer film composition was significantly influenced by the underlying substrate material.