A STUDY OF THE INITIAL-STAGES OF THE OXIDATION OF SILICON USING THE FRESNEL METHOD

The initial stages of the oxidation of silicon are studied using a new analytical technique which we have developed for use in the transmission electron microscope. This technique, the Fresnel method, is based on the use of a through-focal series of images of an interface viewed edge-on to characterise any compositional discontinuity across it. The appearance of the Fresnel fringes seen along the interface as a function of defocus, as matched with computer models, can be used to determine the change in elastic scattering behaviour of the material due to the change in projected potential at such a compositional discontinuity. A set of relatively low-resolution images is used to provide high-resolution data on both the form and the magnitude of the composition change present. The method is applied in conjunction with conventional high-resolution imaging to study the relationship between the structural and stoichiometric changes occurring at the interface between silicon and its oxide. The compositional development of the Si/SiO2 interface as the oxidation progresses in the thickness range 0-5 nm is characterized and related to a model of the initial stages of oxidation.