The application of Moiré effect for testing of a lithographic projection lens is reported. The arrangement presented allows measuring magnification, distortion, field curvature and telecentricity of the lens and can be used for its fine tuning. The method is based on two matched two-dimensional gratings, positioned in mutually conjugated planes; one of them can be translated. Visual interpretation of Moiré fringe pattern allows quick diagnostics of position errors exceeding critical dimension, whereas lateral scanning is applied for measuring of smaller magnitude errors. Field curvature and telecentricity are measured by 3D scanning. Presented results are in a good agreement with those obtained elsewhere.
The present research is part of an effort to develop tools that make the lens design process more systematic. In typical optical design tasks, the presence of many local minima in the optical merit function landscape makes design non-trivial. With the method of Saddle Point Construction (SPC) which was developed recently ([F. Bociort and M. van Turnhout, Opt. Engineering 48, 063001 (2009)]) new local minima are obtained efficiently from known ones by adding and removing lenses in a systematic way. To illustrate how SPC and special properties of the lens design landscape can be used, we will present the step-by-step design of a wide-angle pinhole lens and the automatic design of a 9-lens system which, after further development with traditional techniques, is capable of good performance. We also give an example that shows how to visualize the saddle point that can be constructed at any surface of any design of an imaging system that is a local minimum.