Optical Design and Engineering

Design method of off-axis extreme ultraviolet lithographic objective system with a direct tilt process

[+] Author Affiliations
Yan Liu, Yanqiu Li, Zhen Cao

Beijing Institute of Technology, School of Optoelectronics, Key Laboratory of Photoelectronic Imaging Technology and System of Ministry of Education of China, Beijing 100081, China

Opt. Eng. 54(7), 075102 (Jul 08, 2015). doi:10.1117/1.OE.54.7.075102
History: Received April 8, 2015; Accepted June 10, 2015
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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.

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© 2015 Society of Photo-Optical Instrumentation Engineers

Citation

Yan Liu ; Yanqiu Li and Zhen Cao
"Design method of off-axis extreme ultraviolet lithographic objective system with a direct tilt process", Opt. Eng. 54(7), 075102 (Jul 08, 2015). ; http://dx.doi.org/10.1117/1.OE.54.7.075102


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