Photo-induced synthesis of amorphous SiO2 film from tetramethoxy-silane on polymethylmethacrylate at room temperature

A new technique, formation of an SiO2 film on polymethylmethacrylate (PMMA) with tetramethoxysilane (TMOS) as a starting material, by irradiation with a Kr-2 excimer lamp (8.5 eV, 146 nm), and at room temperature was reported. Two photo-induced reactions are involved in this process; the scission of side chains of PMMA and the photochemical reaction of TMOS. The scission of side chains of PMMA with the first irradiation is an essential procedure to fabricate a transparent PMMA coated with TMOS. TMOS coating on PMMA was carried out between the first irradiation and the second irradiation. With the second irradiation, TMOS liquid on the irradiated PMMA turned into a solid which was harder than aluminum. The refractive index of the film is 1.48 +/- 0.03 at 633 nm which is almost the same value as the refractive index of SiO2 fabricated with the thermal oxidation of silicon (1.46). In the infrared spectrum all bands related to alkyl groups disappeared and the line shape was close to that of thermal SiO2. Though etching rate of the film is 10 times faster than that of thermal SiO2, we propose that photo-induced formation of SiO2 having organic impurities of less than 1% succeeded. (C) 1997 Elsevier Science B.V.