Accurate measurements of the density of thin silica films

Using X-ray reflectivity, we investigate UVCVD and PECVD silica thin films deposited on germanium substrates. Under our experimental conditions, an accurate measurement of the total external reflection on the substrate can be obtained. We show that the use of this specific part of the reflectivity profile provides a significant improvement of the density determination of thin films giving an accuracy close to one per cent. This procedure is used to compare the silica densities of films made by UVCVD, PECVD and thermal oxidation. In UVCVD films a stationary deposition regime exists above a critical thickness.