Abstract
Optical projection of masks is a very troublesome task if dimensions are in the submicron range. It is difficult to get an undistorted image in the resist. This problem can be overcome by introducing corrections in the penultimate mask. Till now this has been done by a trial and error method in which an acceptable pattern is made only after a time consuming iterative process.
In this paper a description will be given of the image forming process in which diffraction at the penultimate mask and at the aperture of the lens are the critical features.
Based upon this theory correction formulas are derived for the direct design of penultimate masks. Rules for maximum edge sharpness are given, so that the tolerance demands on the production process can be relaxed.
Extensive experimental measurements are in good agreement with theory. It will be shown theoretically as well as practically that by asymmetrical arrangement of the optical system images of gratings with 0.2–0.3 μm linewidth can be obtained.
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