Influence of Atmospheric Plasma Source and Gas Composition on the Properties of Deposited Siloxane Coatings

Siloxane coatings were deposited using two different atmospheric plasma systems namely a reel-to-reel atmospheric plasma liquid deposition system called Labline (TM) and an atmospheric plasma jet system called PlasmaStream (TM). Both systems combine an atmospheric plasma, with the use of liquid precursors. The influence of the plasma source and processing conditions on the deposited coating properties were studied. The coatings were deposited onto Vycor glass and silicon wafer substrates from a liquid tetraethyl orthosilicate (TEOS) precursor which was nebulized into both He and He/O-2 plasmas. Higher film growth rates were obtained using the plasma jet system; however, the reel-to-reel system facilitated the larger area coating of webs. The thickness (spectroscopic ellipsometry measurements) and water contact angle profile of the films deposited using the jet system on silicon wafer substrates in static mode were investigated. Amongst the other coatings characterization techniques used to evaluate the deposited coatings were optical profilometry, XPS, SEM, and AFM. The formation of particulates due to excess gas-phase reactions during the atmospheric plasma deposition of coatings has been widely reported. In this study, larger number of particulates were observed under the conditions of higher plasma power, with the addition of O-2 into the He plasma and also at low TEOS flow rates. The introduction of N-2 into the He/O-2 plasma, during the deposition of siloxane coatings led to a significant reduction in the number of particulates generated for both plasma sources. Nitrogen gas flow rate was varied systematically and a correlation was obtained on the influence of the flow rate of this gas on surface roughness and particulate formation.