SiOCH films with low dielectric constant were deposited on p-Si(100) substrates using inductively coupled plasma chemical vapor deposition with a mixture of bis-trimethylsilymethane (BTMSM) precursor and oxygen gases. The chemical structure of the SiOCH films deposited at different conditions such as discharge power, BTMSM/O-2 flow rate ratio, and postannealing temperature was studied by Fourier transform infrared spectra. The characterization results indicate that there are at least two ways for C atoms to incorporate into the SiOCH films during deposition. One way is by -CH3 groups attached to Si atoms in Si-O-Si networks, which was caused by a polymerization mechanism, and another is by Si-O-C substructure, which was caused by an oxidation mechanism. The former was the main film growth mechanism when radio frequency (rf) power was lower and the later became dominant while rf power was increased. The transformation of open-linked Si-O-C substructure to ring-linked Si-O-C substructure and the elimination of -OH group were the main reasons of dielectric constant decrease during postannealing procedures. The lowest relative dielectric constant of the film was about 2.1, which was deposited at rf power of 200 W with the BTMSM:O-2 flow rate ratio of 10 sccm: 10 sccm. (C) 2003 The Electrochemical Society.