IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 46, NO. 4, JULY/AUGUST 2010 1661 Xenon Discharge-Produced Plasma Radiation Source for EUV Lithography C. H. Zhang, Member, IEEE, P. Lv, Y. P. Zhao, Q. Wang, S. Katsuki, Senior Member, IEEE, T. Namihira, Senior Member, IEEE, H. Horta, H. Imamura, Y. Kondo, and H. Akiyama, Fellow, IEEE Abstract—Extreme ultraviolet (EUV) radiation with wave- lengths of 11–14 nm is seen as the most promising candidate for a new lithographic technology. Compared with synchrotron radiation sources and laser-produced plasmas, gas discharge- produced plasma sources for EUV radiation are expected to offer lower cost of ownership. Using xenon, a broadband emission in the investigated wavelength range from 10 to 17 nm is observed. Very short current pulses, having a fast rise time of 85- or 140-ns du- ration and 23-kA amplitude, were applied across the xenon-filled Z -pinch capillary (3-mm diameter and 5-mm length) to produce EUV radiation. An EUV radiation from the Z -pinch plasma was characterized, which is based on the temporal behavior of EUV intensity and the pinhole images. Two maximum EUV radiations occur, which are sensitive to the xenon flow rate and the discharge current. The first radiation is relatively of short duration, while the second radiation lasts as long as the first period of the current flows. The EUV source size due to the first radiation is approxi- mately 300 μm, i.e., half of the one due to the second radiation. Index Terms—Discharge plasma, extreme ultraviolet (EUV) sources, xenon emission, Z -pinch. I. I NTRODUCTION T HE APPARENTLY unstoppable advance of miniatur- ization continues. However, soon the limits of optical- exposure technology will be reached. Extreme ultraviolet (EUV) lithography is opening up a new chapter in semiconduc- tor development. It is the leading contender to establish next- generation lithography that makes possible features as small as 50 nm [1]–[4]. A critical issue is the development of a source- emitting radiation with high power and lifetime at a wavelength of 13.5 nm for the optical systems required. EUV radiation Manuscript received December 15, 2005; accepted November 11, 2009. Date of publication May 24, 2010; date of current version July 21, 2010. Paper MSDAD-09-ILDC0507, presented at the 2005 Industry Applications So- ciety Annual Meeting, Hong Kong, October 2–6, and approved for publication in the IEEE TRANSACTIONS ON I NDUSTRY APPLICATIONS by the Industrial Lightning and Displays Committee of the IEEE Industry Applications Society. This work was supported in part by NEDO, in part by the 21st Century COE Program conducted by Kumamoto University, and in part by the National Natural Science Foundation of China (60838005). C. H. Zhang is with the Department of Electrical Engineering, Harbin Insti- tute of Technology, Harbin 150001, China, and also with the ENCS, Concordia University, Montreal, QC H3G 1M8, Canada (e-mail: zch852@gmail.com). P. Lv is with the Department of Electrical Engineering, Harbin Institute of Technology, Harbin 150001, China. Y. P. Zhao and Q. Wang are with the National Key Laboratory of Tunable Laser Technology, Harbin Institute of Technology, Harbin 150001, China. S. Katsuki, T. Namihira, H. Horta, H. Imamura, Y. Kondo, and H. Akiyama are with the Graduate School of Science and Technology, Kumamoto Univer- sity, Kumamoto 860-8555, Japan. Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TIA.2010.2051059 Fig. 1. Schematic diagram of the Z-pinch EUV source. can be produced in two different processes which are currently competing for the lead: laser-produced plasmas (LPP) [4]–[6] and gas discharge-produced plasma (DPP) [3], [7]–[9]. In both approaches, xenon is the predominant target gas due to its con- siderable emission around 13.5 nm, i.e., in the EUV, although oxygen and lithium also emit the characteristic EUV radiation. Additionally, tin (Sn) is realized as another promising discharge medium [9]. The aim is to produce as many photons as possible in the required wavelength range. For LPP, pulsed-laser light is focused on a beam of xenon clusters or liquid xenon. The technique, however, presents a number of problems. Pulsed lasers with pulse duration of around 10 ns and with an average output power of a few kilowatts are required. Also, the process is extraordinarily difficult to control. For this reason, the interest in DPP EUV radiation sources is increasing. DPP produce the xenon plasma through a pulsed discharge of electrically stored energy; the hot and dense plasma is generated here by means of pinching magnetic compression of the discharge plasma. Compared with LPP, the DPP source has drawn much attention in the last decade due to its simplicity and cost-effectiveness. In our studies, EUV radiation from xenon-filled fast capillary Z -pinch discharge has been made, and the emission spectrum around 13.5 nm and pinhole imaging has been measured [8]. The very short current pulses, with a fast rise time of 85- or 140-ns duration and 23-kA amplitude, were applied across 0093-9994/$26.00 © 2010 IEEE