Synthesis of SiO2 Thin Films by Sol-Gel Method Using Photoirradiation and Molecular Structure Analysis

The SiO2 thin films were prepared by a process which combines a sol-gel method and photoirradiation. The HF etch rate and microhardness of a film prepared by this process were better than those of a film furnace-fired at same temperature. The Raman and Si-29 solid state NMR spectra of film prepared by this process were similar to those of a film furnace-fired at higher temperature. There are many unstable folded non-linear SiO2 species in the film prepared at low temperature. On treatment at higher temperature, unstable folded non-linear Si-O-Si rearranges to the stable linear Si-O-Si bond. Photoirradiation enhances this structure change. The process provided denser and harder SiO2 thin films, even at low temperature, than the conventional furnace-firing method did.