Synthesis, properties, and molecular structure analysis of SiO₂ thin films prepared by sol-gel method

SiO₂ thin films were prepared by the sol-gel method. The properties of the films such as film thickness, etching rate in hydrofluoric acid, Vicker's hardness, and the effect of the thermal treatment on the molecular structure were investigated. As a result, it was found that the etching resistance and hardness were improved as the treatment temperature increased. These changes in the properties were related to the density and water content in the film. The molecular structure analysis by the ²⁹Si solid-state NMR and Raman spectroscopy revealed that the unstable distorted Si-O-Si bonds formed in the solution were broken and stable straight Si-O-Si bonds were formed during the high-temperature treatment. As the number of the stable Si-O-Si bonds increases, the hardness and density of the films increases.