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

Abstract

Downloaded From: http://opticalengineering.spiedigitallibrary.org/ on 08/17/2015 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspxAbstract. 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. Downloaded From: http://opticalengineering.spiedigitallibrary.org/ on 08/17/2015 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx Zhen Cao received his BS degree in optoelectronic information engineering from Xi'an Technological University in 2008. He is currently a PhD candidate directed by Prof. Yanqiu Li in the School of Optoelectronics at Beijing institute of Technology. His current interests include the optical system design for EUVL. Optical Engineering 075102-7 July 2015 • Vol. 54(7) Liu, Li, and Cao: Design method of off-axis extreme ultraviolet lithographic objective system. . . Downloaded From: http://opticalengineering.spiedigitallibrary.org/ on 08/17/2015 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

Design and exploration of freeform three-mirror imaging systems with integrated primary and tertiary mirrors using same expression

“…The decenter and tilt of mirrors will induce unconventional aberrations with special field dependence 4 , which will be well matched by the aberration that the freeform surfaces induced 5,6 . Therefore, the freeform surfaces have been successfully used in many domains [7][8][9][10][11][12][13] .…”

Review of optical freeform surface representation technique and its application

“…Applications of optical freeform surfaces in the nonimaging category include beam shaping, 3 concentrators, 4 and illumination, 5 where optical freeform surfaces can control the light direction to improve energy uniformity and efficiency. Examples of applications in the imaging category are ultrashort projection lenses, 6 head-mounted displays, 7 ultraviolet lithographic objectives, 8 and off-axis reflective infrared imaging systems, 9 where optical freeform surfaces are used to improve imaging performance and compactness. Hence, freeform optics is regarded as the next-generation and ground-breaking technology in modern optics.…”