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.