Paper PS1-ThM11
Influence of Air and Water Vapour Contaminations on the Atmospheric Pressure PECVD of Fluorocarbon Thin Films

Thursday, October 23, 2008, 11:20 am, Room 304

Low pressure plasma-enhanced chemical vapour deposition (PECVD) of fluorocarbon films has been extensively studied in the last decades. Very recently atmospheric pressure dielectric barrier discharges (DBDs) have been addressed as an attractive route towards the deposition of fluoropolymers, nevertheless, the utilization of this approach is still a challenge. Research efforts should be devoted to evaluate if DBDs can actually be advantageous compared to low pressure plasmas; for this purpose, besides the fundamental investigation of fluorocarbons fed DBDs, it is also important to gain insights into the influence of contaminants such as air and water vapour. The presence of these contaminants into the atmospheric pressure reactor could have, in fact, serious detrimental effects on the overall deposition process because it might result in a drastic decrease of the F/C ratio of the films, in the uptake of oxygen and nitrogen as well as in deposition rate reduction. On the other hand, the knowledge of the highest level of contamination compatible with an acceptable process performance and consequently the possibility of depositing fluoropolymers in “contaminated” environments could allow to reduce the cost of plasma processes and reactors. For these reasons we decided to evaluate the influence of air and water vapour contaminations on the PECVD of fluoropolymers in atmospheric pressure cold plasmas. Controlled amounts of air and water vapour have been added to a DBD fed with argon-hexafluoropropene (Ar-C₃F₆). The discharge regime has been clarified by electrical measurements, while film characteristics have been studied by FTIR, XPS, WCA measurements and SEM. Gas phase has been investigated by optical emission spectroscopy and the stable species contained in the gas effluent have been analyzed using gas chromatography coupled with mass spectrometry, in order to have indications on the reactive fragments generated inside the discharge. The results obtained in this work show that Ar-C₃F₆ DBDs allow to deposit coatings with a deposition rate of 56 nm/min and a XPS F/C ratio of 1.7. Contaminants addition causes a slight variation of the F/C ratio and a decrease of the deposition rate. In particular, if the [Air]/[C₃F₆] and [H₂O]/[C₃F₆] ratios in the feed are kept below 0.25 and 0.125, respectively, the variation of the F/C ratio is negligible and the deposition rate remains higher than 45 nm/min.