Microstructure developments of F-doped SiO2 thin films prepared by liquid phase deposition

This study presents a systematic investigation of the microstructure dependence of liquid phase deposition (LPD) of SiO₂ films on solution parameters and deposition temperature. The corresponding deposition rate and film roughness were also evaluated under various deposition conditions. Smooth and sufficiently dense SiO₂ films, which are the prerequisite for reliable low-k dielectric applications, were deposited on both silicon and fluorine-doped tin oxide coated glass substrates from supersaturated hydrofluorosilicic acid (H₂SiF₆) solution with the addition of boric acid (H₃BO₃). It is shown that H₂SiF₆ acid controls the surface morphology and grain structure through surface reaction while H₃BO₃ acid prompts bulk precipitation in solution. For the 208-nm thick SiO₂ film, the breakdown field exceeded 1.9 MV/cm and the leakage current density was on the order of 10^− 9 A/cm² at 4 V, indicating excellent insulating properties of LPD SiO₂ films. The strong presence of Si-O-Si and some Si-F with little Si-OH bond as shown in FT-IR spectra indicate that the LPD SiO₂ films have mostly a silica network with some fluorine (F) content. F-doping was self-incorporated into the silica films from the H₂SiF₆ solution during deposition process.