The Influence of Multilayers on the optical-Performance of Extreme UltraViolet Projection Systems

摘要

Extreme Ultraviolet (EUV) projection systems consist of reflective optics, as the 13.4 nm illuminating radiation is highly absorbed in all materials. The reflectors are multilayers, which typically consist of alternating layers of molybdenum and silicon. The multilayers entail important consequences for the imaging properties, such as resolution, depth of focus and tolerances. To incorporate the influence of multilayers in optical design software an approach using the effective reflective depth is proposed. A new method to calculate the spatially varying optimum thickness of multilayers ('grading') is presented.