A transparent low refractive index SiO2 film was laminated on a glass substrate with photochemical reaction by an Xe2* excimer lamp in the presence or NF3, 02 and silicon wafer at room temperature. The glass substrate and the silicon wafer were placed in the reaction chamber, which was filled with NF3 and O2 gases in the mixing ratio of 10:1 and under 330 Torr. The Xe2* excimer lamp was, then, irradiated for 20 minutes. The SiO2 film was spontaneously laminated on the glass substrate by repeating an adsorption of SiF4 and a photochemical oxidization with NO2, which was photo-dissociated from a mixed gas of NF3 and O2. The film thickness was 160 nm and the infrared spectrum was measured; the Si-O peaks were depicted at 600, 700, 1100[1/cm-1]. And Si-F peak was observed at 740[1/cm-1]. Then, the refractive index of the SiO2 film was 1.36. After annealing the film for one hour at 200 degree, the refractive index increased to 1.42.