This paper presents the results of the characterization of porous silica films used as intermetal dielectrics. The films were fabricated via sol-gel process using tetraethyl orthosilicate (TEOS) and methyltriethoxysilane (MTES) as precursors with acid and base as catalysts. Several advanced techniques such as transmission electron microscopy, specular X-ray reflectivity, Fourier transform infrared spectroscopy, nitrogen adsorption, thermal gravimetric, and differential thermal analysis have been employed to obtain information on the structural properties of the films and reaction mechanisms involved in the sol-gel process of such dielectrics. The characterization results show the effects of the TEOS/MTES ratio on the development of the porosity, pore size, and pore interconnectivity of the films, which reflects the influence of different mechanisms of hydrolysis and condensation of silica precursors in different pH conditions and the existence of covalently bonded organic ligands on the pore structure. An inherently low dielectric constant of around 2.0 was realized for about 60% porosity in the silica films. The pore sizes were less than 10 nm with majority of pores being closed-cells. (C) 2003 The Electrochemical Society.