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Optical Engineering

Aspherical surfaces design for extreme ultraviolet lithographic objective with correction of thermal aberration
Author(s): Yan Liu; Yanqiu Li
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Paper Abstract

At present, few projection objectives for extreme ultraviolet (EUV) lithography pay attention to correct thermal aberration in optical design phase, which would lead to poor image quality in a practical working environment. We present an aspherical modification method for helping the EUV lithographic objective additionally correct the thermal aberration. Based on the thermal aberration and deformation predicted by integrated optomechanical analysis, the aspherical surfaces in an objective are modified by an iterative algorithm. The modified aspherical surfaces could correct the thermal aberration and maintain the initial high image quality in a practical working environment. A six-mirror EUV lithographic objective with 0.33-numerical aperture is taken as an example to illustrate the presented method. The results show that the thermal aberration can be corrected effectively, and the image quality of the thermally deformed system is improved to the initial design level, which proves the availability of the method.

Paper Details

Date Published: 29 September 2016
PDF: 6 pages
Opt. Eng. 55(9) 095108 doi: 10.1117/1.OE.55.9.095108
Published in: Optical Engineering Volume 55, Issue 9
Show Author Affiliations
Yan Liu, Beijing Institute of Technology (China)
Yanqiu Li, Beijing Institute of Technology (China)

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