Process Diagnostics in High-Aspect-Ratio Patterns by Microscopic Interferometry

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In ULSI (ultra large scale integration) fabrication, an in-situ monitoring tool for high-aspect-ratio pattern processing is required. In this work we have aimed the development and its performance characterization of a new diagnostic method based on an interferometric technique combined with an optical microscope. In the first year, we developed the basic construction of two-dimensional interferometric microscopy by using a monochromatic laser source, a Michelson interferometer and a high sensitive CCD (charge coupled device) camera. In the second year, we put much effort to solve a tough problem due to the disturbance by mechanical vibrations by adopting a mechanically stiff structure and a computational technique for compensating the distortion.In the latter half of this project, we tried to apply this technique to a realistic problem. One of the urgent problem in the currently used plasma etching process of SiO2 is the improvement of etching selectivity to underlying or protecting materials such as Si, SiィイD23ィエD2 NィイD24ィエD2 and photo-resist. We used this method in the precise in-situ measurement of etching rates for these materials under various plasma conditions of fluorocarbon gases. From the results the reactions in the gas phase and on the substrate surface and their controlling methods are argued for realizing better selectivity.