INSTITUTE OF PHYSICS PUBLISHING JOURNAL OF PHYSICS D: APPLIED PHYSICS J. Phys. D: Appl. Phys. 37 (2004) 3266–3276 PII: S0022-3727(04)84475-9 EUV discharge light source based on a dense plasma focus operated with positive and negative polarity I V Fomenkov, N B¨ owering, C L Rettig, S T Melnychuk, I R Oliver, J R Hoffman, O V Khodykin, R M Ness and W N Partlo Cymer Inc., 17075 Thormint Ct, San Diego, CA 92127, USA Received 29 July 2004, in final form 15 October 2004 Published 19 November 2004 Online at stacks.iop.org/JPhysD/37/3266 doi:10.1088/0022-3727/37/23/007 Abstract The application of a dense plasma focus pinch discharge as a light source for extreme ultraviolet (EUV) lithography is discussed. For operation with xenon gas, the radiation emitted at around 13.5 nm is analysed with temporal, spectral or spatial resolution. We describe and compare the operating characteristics and plasma dynamics of the device when energized at positive and negative polarity of the charging voltage. The thermal load distribution, heat deposition and wear of the electrodes are measured and compared for both configurations. High-repetition rate burst mode data show characteristic transients. Source size data are also obtained when tin powder is used as the target element. More favourable performance characteristics were generally obtained for operation of the pinch discharge at negative polarity. (Some figures in this article are in colour only in the electronic version) 1. Introduction Lithography at extreme ultraviolet (EUV) wavelengths has been chosen by the semiconductor industry as the main contender for future chip manufacturing at the 32 nm node and beyond. Significant research and development efforts have already been devoted to this technology during the last five years. The EUV programme is presently gaining momentum; critical challenges and technology hurdles in key areas are actively addressed and solved to meet the aggressive road maps that are in place to reach high-volume manufacturing with EUV exposure tools at the end of this decade. A pulsed plasma light source with extremely high power and brightness is required for integration into a stepper tool based on all-reflective optics with multilayer (ML) coatings. The mirror reflectance at normal incidence is only ∼70% for each surface; thus only a small fraction of the radiation produced will reach the wafer. Therefore, to achieve high production throughput, the EUV source power has to be in the range of 80–120 W within a bandwidth of 2% at the wavelength of choice, 13.5 nm, with high spectral purity. Repetition frequencies of more than 6000 Hz and integrated (50-pulse) energy stabilities of ±0.3% are needed to meet the dose requirements of the scanner tool. Furthermore, the demand for brightness leads to a source etendue in the range of 1–3.3 mm 2 sr with a maximum input solid angle to the illuminator section of 0.2 sr. Source cleanliness is also very important and translates to a lifetime requirement of more than 30 000 h. At Cymer, we have chosen a dense plasma focus (DPF) configuration for development efforts devoted to a discharge-produced plasma (DPP) source targeted for EUV technology. The plasma focus concept was initiated long ago by the pioneering work of Filippov et al [1] and Mather [2]. Apart from the main application of large-scale DPF devices in fusion research, small-energy down-scaled instruments (with less than ∼1 kJ stored energy) were also investigated in the past by several groups and operated at higher repetition frequencies to serve as intense radiation sources [3–9]. In addition, the application of a DPF to proximity x-ray and soft x-ray lithography was discussed [10–15]. Our choice of source configuration was born out of past development work on coaxial plasma guns and plasma thrusters for space 0022-3727/04/233266+11$30.00 © 2004 IOP Publishing Ltd Printed in the UK 3266