Effects of methyl and perfluoro-alkyl groups on water repellency of silicon oxide films prepared by microwave plasma-enhanced chemical vapor deposition

Silicon oxide films with water repellency were prepared by microwave plasma-enhanced chemical vapor deposition using multiple gas mixtures of five organosilicon compounds, fluoro-alkyl silane (FAS-17) and Ar as source gases. We studied the effects of methyl and perfluoro-alkyl groups in the reactants on the water repellency of the films. Films of different compositions were prepared by controlling the partial pressures of the reactants. High water repellency was obtained when tetramethylsilane and trimethylmethoxysilane were mixed with FAS-17/Ar. Water repellency depended on the number of methyl groups in the organosilicon compounds and did not depend directly on the fluorine concentrations at the surfaces of the films. The decomposition process of reactants in the plasma was analyzed by optical emission spectroscopy.