Effect of process parameters on chemistry, growth rate and nano-sized particulate formation of atmospheric plasma deposited, nm thick siloxane coatings.

Nano-thick siloxane coatings with thickness in the range 1-33 nm were deposited using a reel-to-reel atmospheric plasma coating system. The coatings were deposited from a tetraethoxysilane (TEOS) precursor which was nebulised into a helium plasma. An issue influencing coating performance is the incorporation of particulates, which are formed during the deposition process. By systematically varying the process parameters such as plasma power, TEOS flow rate, gas flow rates (He, O2, and N2), a correlation was obtained between the deposition conditions and particulate formation. The effect of process parameters on growth rate, changes in coating chemistry and particulate formation on the deposited nm-thick films were studied by spectroscopic ellipsometry, contact angle/surface energy measurements, optical profilometry, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray reflectometry (XRR), Scanning electron microscopy (SEM) and Atomic force microscopy (AFM). Larger numbers of particulates were formed under the conditions of higher plasma power, with the addition of O2 or N2 into the He plasma and also at both very low and high TEOS flow rates in the range 10-200 microl/min. Low plasma input power and moderate precursor flow rates (approx. 25 microl/min) significantly reduced particulate formation.