In situinfrared fibre evanescent wave spectroscopy as a diagnostic tool for plasma polymerization in a gas discharge

A novel diagnostic technique is proposed for the in situ sensing of thin organic film deposition in gas discharge plasmas. The method is based on the evanescent wave spectroscopy using an infrared fibre, and allows one to analyse the molecular structure of a growing plasma polymer film in the process reactor. The styrene plasma polymerization on a fibre in the plasma bulk of a capacitively coupled rf discharge was studied. The infrared fibre sensor provides higher sensitivity than the crystals of comparable geometry usually employed in attenuated total reflection spectroscopy. Accumulated evanescent wave infrared absorption spectra give information not only on the molecular structure of the deposited films, but also on its time evolution during the deposition. It was also possible to make conclusions on the molecular orientation of plasma polymerized styrene films deposited under the various process conditions. The fibre was regenerated in an oxygen plasma. The etching process results in the destruction of phenyl rings and the ablation of the plasma polymer film from the surface of the fibre core.