The surface roughness, infrared absorption, and index of refraction characteristics of SiO2 films prepared with various commonly used techniques are discussed. According to the atomic force microscopy images, thin oxides (100 angstrom or less) have smooth surfaces with an rms surface roughness of about 4 angstrom. The roughness increases slightly with the increase of the film thickness to about 1000 angstrom. Oxide films prepared by low-pressure chemical vapor deposition pyrolytic decomposition of SiH4/O2 mixtures, electron-beam (e-beam) evaporation, and microwave plasma decomposition of SiH4/O2 gas mixtures exhibit rougher surfaces with an rms surface roughness exceeding 20 angstrom. In particular, the atomic force microscopy images obtained in films prepared by e-beam evaporation and microwave plasma decomposition reveal the presence of microvoids and pinholes which probably facilitate the diffusion of water vapor into the oxide after film deposition. This later aspect was inferred from infrared absorption data which show absorption bands associated with atomic motions of Si-OH and H-0-H groups.