ABSTRACT
This chapter examines the design considerations, difficulties, solutions, and techniques of designing the optical systems from source to reticle. It discusses the creation of a field of multiple sources with the use of kaleidoscopes, fly’s eyes, and other devices to produce a uniform plane. The manufacturers of high-pressure mercury lamps have optimized the lamp designs specifically for use in microlithography, targeting the spectral lines 436 nm, 365 nm, and 248 nm. In a microlithographic system the illuminator has great influence on the robustness and quality of the exposure in the photo-resist. Circuit patterns printed in microlithography are often classified, for diagnostic purposes, as dense lines, isolated lines, and contacts. Lithographic technique that enhances resolution involves imaging with phase-shifting masks. All lithographic projection lenses are designed to be telecentric on the image side, in order to maintain the same magnification through the depth of focus.
