ABSTRACT
This chapter examines the design considerations, difficulties, solutions, and techniques of designing the optical systems from the source to reticle. Like photography, imaging optics allows the parallel transfer of tremendous amounts of information from the object to image, or the reticle to wafer, in a fraction of a second. The specialized projection lenses of microlithography must accomplish this image transfer while maintaining uniformity of imagery and image placement on the nanometer level over centimeter sized image fields. The illuminator has an aperture stop that is imaged into the projection lens' aperture. Examining the pupil maps of kaleidoscope patterns in the aperture stop is a useful way to analyze the imaging requirements of the entrance pupil to the aperture stop. The chapter covers the theory of partial coherent imaging without delving into the equations of image formation. The lamp designs of high-pressure mercury lamps have specifically been optimized for use in microlithography.
