Silica sol synthesized by molecular template method combined with a two-step acid/base catalyst process was deposited on Si (100) substrate by spin coating. Then the wet gel film was modified with trimethylchlorosilane (TMCS). The porosity and corresponding dielectric constant measured through ellipsometry were 78% and 1.66, respectively. Thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) were employed to analyze the properties of the films at different preparing and post-treating conditions. The difference among surface morphology of the silica xerogel films with variant preparing processes was clearly observed by scanning electron microscopy (SEM). The film with the lowest dielectric constant and leakage current density measured by high-resistance potentiometer was obtained through the optimized process, which is very satisfactory for inter-metal dielectric application. (C) 2004 Elsevier B.V. All fights reserved.