Process for fabricating a device using polarized light to determine film

Abstract

A process for device fabrication in which polarized light is used to monitor film thickness. The polarized light is made incident on the surface of a substrate with a film thereon that has a different reflectivity than that of the underlying substrate. The surface of the film is non-planar, either by virtue of the fact that the film is formed over a substrate with a non-planar surface, or because there is a patterned layer formed over the film, or both. The substrate is subjected to conditions that change the thickness of the film on the substrate. The polarized light that is reflected from the substrate is detected at a selected wavelength or wavelengths and a trace of the intensity of the reflected light both parallel and perpendicular to the substrate surface over time is obtained. This trace is compared to a model trace which is obtained by approximating the film thickness, and the relative amount of the areas of different reflectivity on the substrate surface. The film thickness used to generate the model trace is adjusted to obtain a desired correspondence between the model trace and the actual trace. When the desired correspondence is obtained, then the film thickness used to obtain the model trace with the desired correspondence is the determined film thickness.