PHOTOINDUCED 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 irradi ation with a Kr-2 excimer lamp (8.5 eV, 146 nm), and at room temperatu re was reported. Two photo-induced reactions are involved in this proc ess; the scission of side chains of PMMA and the photochemical reactio n of TMOS. The scission of side chains of PMMA with the first irradiat ion is an essential procedure to fabricate a transparent PMMA coated w ith TMOS. TMOS coating on PMMA was carried out between the first irrad iation and the second irradiation. With the second irradiation, TMOS l iquid 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 fabric ated with the thermal oxidation of silicon (1.46). In the infrared spe ctrum 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-indu ced formation of SiO2 having organic impurities of less than 1% succee ded. (C) 1997 Elsevier Science B.V.