Abstract: Crack-free homogeneous nanoporous silica films on silicon wafers were synthesized via supercritical drying of wet gel films obtained by spin coating the polymeric silica sol using the sol-gel method
with tetraethoxysilane(TEOS) as precursor and poly(ethylene glycol)(PEG) as additive. The nanoporous silica films were characterized by FTIR, TG-DTA, AFM and spectroellipsometer. The surface of silica
films prepared with PEG was rough compared to that of films without PEG. The silica film with PEG had higher porosity and lower dielectric constant. Its dielectric constant could be reduced below 2.0.
PEG not only participated in but also modified the sol-gel process of TEOS. The silica film with PEG originally was hydrophilic because of its Si--OH structure and then became hydrophobic after modified
with trimethylchlorosilane(TMCS).

Key words: nanoporous silica film, sol-gel, poly（ethylene glycol）, low dielectric constant