1 July 1988 Capacitive Focusing Method For Microlithography
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Focusing is a critical requirement in optical microlithography. The high resolution required calls for a large relative aperture, and this in turn shortens the depth of focus. Depth of focus on the order of the wavelength of light is a major technical problem, especially if one does not impose narrow tolerances on the flatness of the substrate. Here we report on a capacitive focusing method that makes feasible focusing accuracies to a fraction of a micrometer, automatically if desired. The theory, an implementation, and results obtained are presented.
Meir Nitzan, Jack Broder, Naftali Eisenberg, Leo Levi, "Capacitive Focusing Method For Microlithography," Optical Engineering 27(7), 277512 (1 July 1988). https://doi.org/10.1117/12.7976715

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