Controlled thickness and dielectric constant titanium doped SiO₂ thin films on silicon by sol-gel process

In this paper, we report the preparation of crack-free relatively thick (a few μm) SiO₂-TiO₂ thin films on silicon substrates using the sol-gel spin-coating method. The influence of the process parameters on the quality of the film, such as the solution condition, the spin-coating speed, the heat treatment temperature and time, have been studied. We found that the cracking of the film could be avoided by selecting the right sol composition ratios, adding PVA (polyvinyl alcohol) to the sol and properly controlling the heat treatment. Most importantly, we discovered that by polishing the edges of the film after the deposition of each single layer, the number of such layers that deposited without crack formation could be substantially increased. The refractive index (or dielectric constant) profile and thickness of the film have been determined using prism coupling technique and the inverse WKB method. The refractive index was found to depend on the content of Ti0₂ as well as the heat treatment condition. Using an AFM (Atomic Force Microscopy), the surface morphology of the film was found to be good.