X-ray reflectivity is a powerful probe of thin film morphology. It can be used to nondestructively determine the interface and surface roughness, thickness, and density of the layers. This paper presents the application of the technique to the case of Si02on Si. Experimental reflectivity results with a dynamic range of 106 have been obtained on a number of oxide layers prepared using processing conditions. The reflectivity oscillations caused by oxide layers could be easily observed over this entire range, and significant differences were observed between samples. In particular, a plasma enhanced chemical vapor deposition grown oxide is found to have an interfacial layer of lower density. © 1990, American Vacuum Society. All rights reserved.