X-ray scattering studies of thin films and surfaces: thermal oxides on silicon

Abstract

A triple-axis X-ray spectrometer has been used to examine the reflectivity and surface scattering from silicon wafers with various thicknesses of oxide surface layers (from 10 to 100 AA). The X-ray techniques provide accurate information on the thickness of the surface oxide layer, the electron density of the roughness of both the surface interface and the substrate to layer interface. The use of a triple-axis spectrometer has two important advantages over the more conventional X-ray reflectivity techniques. It allows accurate reflectivity measurements to be carried out on samples which are, macroscopically, far from flat, such as semiconductor wafers in preparation for device fabrication. It also enables the intensity of the specularly reflected X-ray beam to be measured without contamination from the appreciable small-angle scattering which can occur from a microscopically rough surface. To illustrate this point, reflectivity measurements from a high-quality glass optical flat are also described.