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Optical Engineering

Design method of off-axis extreme ultraviolet lithographic objective system with a direct tilt process
Author(s): Yan Liu; Yanqiu Li; Zhen Cao
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Paper Abstract

An off-axis extreme ultraviolet (EUV) lithographic objective can achieve a high numerical aperture (NA) beyond 0.33 with only six mirrors due to the efficient separation of the ray path, which greatly improves the resolution and energy utilization. A method is developed to design an off-axis lithographic objective with six mirrors. The method starts with a coaxial system with ray vignetting caused by increase of the NA. To avoid the ray vignetting, a reasonable range of solution for the tilt angle of each mirror is determined by real ray calculation. A set of optimal solutions for tilt angles of mirrors, which corresponds to the minimal composite root-mean-square wavefront error, is found from the reasonable ranges of solutions by a search program. In this way, an initial off-axis configuration without ray vignetting can be directly obtained and it is suitable for further optimization. To demonstrate the practicability of the method, an off-axis design example is given which shows that the presented method provides an efficient process to get to initial configuration for off-axis EUV lithographic objective with six mirrors.

Paper Details

Date Published: 8 July 2015
PDF: 7 pages
Opt. Eng. 54(7) 075102 doi: 10.1117/1.OE.54.7.075102
Published in: Optical Engineering Volume 54, Issue 7
Show Author Affiliations
Yan Liu, Beijing Institute of Technology (China)
Yanqiu Li, Beijing Institute of Technology (China)
Zhen Cao, Beijing Institute of Technology (China)


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