A silica film was formed on a polycarbonate substrate by a plasma CVD technique using tetraethoxysilane (TEOS), a kind of organosilicone compound, and N
2O gas as the raw materials. Adding Ar gas with TEOS to a reactor significantly improved adhesion between the silica film and the polycarbonate substrate, with the improvement becoming more pronounced as the quantity of Ar gas was increased. This phenomenon was observed only when TEOS and N
2O gas were used and was not seen with SiH
4 and N
2O gas. XPS analysis indicated that decomposition of the phenyl groups of the substrate was accelerated with an increasing quantity of Ar gas, resulting in the formation of C-O, C=O groups. Based on these results, the following reaction mechanism is thought to occur on the substrate. Excited Ar gas and the reaction intermediates of TEOS, in which the main structure should be -Si-O-, are formed initially in the plasma state. Then, C radicals are generated on the substrate surface as a result of the attack by excited Ar gas. The C radicals combine with the reaction intermediate of TEOS, and finally -Si-O-C- bonds are formed. These bonds work to improve adhesion between the silica film and the substrate.
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