Photoinduced synthesis of amorphous SiO2 with tetramethoxysilane

Photoinduced fabrication of amorphous SiO2 (a-SiO2) film is examined with tetramethoxysilane (TMOS) at room temperature. The photoinduced reactions consist of two steps: photoexcitation of silicon substrate and photoinduced synthesis of a-SiO2. The surface of the irradiated silicon with the Xe-2 excimer lamp peaking at 7.2 eV is covered with silanol groups. Although the TMOS is difficult to coat on a silicon substrate because of its high volatility, the TMOS can be coated on the irradiated silicon wafer. The increase of the cohesive power is thought to originate from silanol groups on silicon generated with irradiation. Infrared absorption related to the methyl group in TMOS disappeared with illumination in the second step. The line shape of IR absorption turns to be similar to that of thermal SiO2 on silicon. The dependence of photon energy for illumination is also examined. The refractive index of SiO2 synthesized from TMOS is 1.453 at 633 nm, which is almost the same as the refractive index of thermal SiO2. Finally, a model of photochemical reaction is proposed. (C) 1996 American Institute of Physics.