Image-based pupil plane characterization for anamorphic lithography systems

Abstract

Next-generation EUV lithography systems will use anamorphic optics to achieve high-NA. The well-known Zernike circle polynomials do not describe the sixteen primary aberrations of these anamorphic optical systems though. We propose to use a basis which does describe the primary aberrations. We examine the properties of this new basis and how they impact lithographic processes through analogies to isomorphic aberrations. We have developed an application to use the proposed basis in existing lithography simulators. There is an additional importance in EUVL placed on understanding how pupil variation evolves during system operation. Interferometric methods are the de facto standard of pupil phase metrology but are challenging to implement during tool use. We have previously presented an approach to measure both the pupil amplitude and phase variation of isomorphic EUVL systems from images formed by that system. We show how this methodology can be adapted to anamorphic optical systems. More specifically, we will present a set of binary metrology targets sensitive to the anamorphic primary aberrations.