A process for depositing porous silicon oxide-based films using a sol-gel approach utilizing a precursor solution formulation which includes a purified nonionic surfactant and an additive among other components, where the additive is either an ionic additive or an amine additive which forms an ionic ammonium type salt in the acidic precursor solution. Using this precursor solution formulation enables formation of a film having a dielectric constant less than 2.5, appropriate mechanical properties, and minimal levels of alkali metal impurities. In one embodiment, this is achieved by purifying the surfactant and adding ionic or amine additives such as tetraalkylammonium salts and amines to the stock precursor solution.