Silicon dioxide films deposited by electron cyclotron resonance chemical vapor deposition have been characterized using Fourier transform infrared spectroscopy, Rutherford backscattering spectrometry, and ellipsometry. A commercially available reactor was used to generate a high-density plasma at low total gas pressures (3-4 mTorr). A gas mixture of Ar, O2, and SiH4 was used to deposit SiO2 films on 200 mm Si substrates at temperatures less than 450-degrees-C for interlayer dielectric applications. The dielectric constant of the films was measured using metal oxide semiconductor capacitors. Relationships between the dielectric constant and the refractive index, Si-OH content, and film stoichiometry were investigated using a model based on the Clausius-Mosotti equation. During the study, the O2 and SiH4 gas flows were adjusted to vary the film properties. Silicon dioxide was deposited over a wide range of O2 and SiH4 gas flow conditions. For SiO2 films, the dielectric constant was strongly correlated with the Si-OH content. At low O2/SiH4 gas flow ratios, suboxide films were deposited and the dielectric constant increased in relation to the refractive index. A low-temperature, postdeposition anneal was investigated as a means to reduce the Si-OH content and dielectric constant of the films. Modeling results indicate that the dielectric constant of SiO2 films can be predicted using measurements of the film thickness, refractive index, and Si-OH content, thus providing a nondestructive technique for monitoring the dielectric constant.