SiO₂ thin films have been grown on Si and MgF₂ wafers at low temperatures in the range of room temperature (R.T.)-200°C by photo-induced chemical vapor deposition (photo-CVD) using synchrotron radiation (SR). The thin films grow selectively on the irradiated area. Deposition rate at R.T. is about 8-13 nm/min, and depends on the electron beam current of SR. The thin films deposited even at R.T. have few impure Si-H and Si-OH bonds, because source gases are decomposed and react effectively, in the vapor phase and on the substrate surface by the SR light. The minimum fixedoxide-charge density is 1.6×10¹¹ cm^-2 in SiO₂ film of thickness 92 nm deposited at R.T. This density is low in comparison with those of films deposited at low temperature by the other CVD methods.