14 October 2004 Avoiding unstable regions in the design space of EUV mirror systems comprising high-order aspheric surfaces
Author Affiliations +
When Extreme Ultraviolet mirror systems having several high-order aspheric surfaces are optimized, the configurations often enter into highly unstable regions of the parameter space. Small changes of system parameters lead then to large changes in ray paths, and therefore optimization algorithms crash because certain assumptions upon which they are based become invalid. We describe a technique that keeps the configuration away from the unstable regions. The central component of our technique is a finite-aberration quantity, the so-called quasi-invariant, which has been originally introduced by H. A. Buchdahl. The quasi-invariant is computed for several rays in the system, and its average change per surface is determined for all surfaces. Small values of these average changes indicate stability. The stabilization technique consists of two steps: First, we obtain a stable initial configuration for subsequent optimization by choosing the system parameters such that the quasi-invariant change per surface is minimal. Then, if the average changes per surfaces of the quasi-invariant remain small during optimization, the configuration is kept in the safe region of the parameter space. This technique is applicable for arbitrary rotationally symmetric optical systems. Examples from the design of aspheric mirror systems for EUV lithography will be given.
© (2004) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Oana Marinescu, Oana Marinescu, Florian Bociort, Florian Bociort, Joseph J.M. Braat, Joseph J.M. Braat, } "Avoiding unstable regions in the design space of EUV mirror systems comprising high-order aspheric surfaces", Proc. SPIE 5523, Current Developments in Lens Design and Optical Engineering V, (14 October 2004); doi: 10.1117/12.559677; https://doi.org/10.1117/12.559677


EUV microlithography: a challenge for optical metrology
Proceedings of SPIE (October 18 2004)
An inflatable circular membrane mirror for space telescopes
Proceedings of SPIE (February 10 2005)
Novel aplanatic design method
Proceedings of SPIE (August 28 2009)

Back to Top