We have previously proposed a method for depositing silicon dioxide films on Si from tetraethoxysilane Si(OC2H5)4 (TEOS) using ultraviolet (UV) light from a low pressure mercury lamp. In the method, an organic solution which contains TEOS is spin-coated onto a Si wafer surface to form a thin organic film which is then exposed to the UV light to synthesize silicon dioxide. The photochemical reactions responsible for the oxide formation and the thermal properties of deposited films have been investigated using infrared (IR) and UV absorption spectroscopy and thermal desorption spectroscopy (TDS). IR and UV absorption data confirm that the UV light decomposes organic compounds in the spin-coated organic film to convert the film into a silicon dioxide film. We show that some photochemical reactions responsible for the decomposition of organic compounds are two-step processes. TDS data demonstrate that the deposited film is stable from substrate heating to approximately 400-degrees-C.