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 SiH4was used to deposit SiO2films on 200 mm Si substrates at temperatures less than 450 °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 O2and SiH4gas flows were adjusted to vary the film properties. Silicon dioxide was deposited over a wide range of O2and SiH4gas flow conditions. For SiO2films, the dielectric constant was strongly correlated with the Si–OH content. At low O2/SiH4gas 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 SiO2films 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.