MM SCIENCE JOURNAL I 2019 I DECEMBER 3406 EUV SOURCE AT HiLASE: THE STATE OF THE ART CHIARA LIBERATORE 1 , MARTIN DUDA 1* , PAWEL SIKOCINSKI 1 , MICHAL CHYLA 1 , AKIRA ENDO 1 , MARTIN SMRZ 1 , TOMAS MOCEK 1 1 HiLASE Centrum, Fyzikalni ustav AV CR, v. v. i. Za Radnici 828, 252 41 Dolni Brezany, Czech Republic DOI : 10.17973/MMSJ.2019_12_2018131 e-mail : martin.duda@hilase.cz An overview of the Extreme Ultraviolet (EUV) source to be constructed in the frame of the Czech national R&D project HiLASE (High average power pulsed LASErs) is presented. The HiLASE EUV source will be devoted to industrial and medical applications, as well as to fundamental studies (such as the chemistry of polymers). This wide variety of different applications depends on the possibility of targeting different EUV wavelengths (namely 13.5 nm and the water window range, 2.33-4.40 nm), which is insured by the fact that the projected table top EUV source can work on multiple different HiLASE lasers: the cryogenically cooled, Yb:YAG slab high energy laser system and the thin-disk, high repetition rate picosecond laser systems. HiLASE EUV source is intended as a user oriented device based on a laser plasma source with single stream gas-puff target. KEYWORDS EUV, tabletop soft x-ray source, ellipsoidal grazing mirror, laser produced plasma, gas target, water window, EUV lithography 1 INTRODUCTION EUV table-top systems based on monochromatic beams are efficient devices used in nanolithography and in the micro/nanostructuring of materials, with a wide range of applications spanning from the fabrication of microchips to the construction and improvements of medical devices [Juha 2002, Fiedorowicz 2004, Bartnik 2005, Juha 2005, Bakursky 2010, Bartnik 2010, Wachulak 2018]. Thus, user-oriented facilities with high-power lasers, such as the HiLASE Centre, express a high interest in developing this type of source. For many years, HiLASE Centre has devoted its efforts to improving EUV sources, mainly decreasing plasma instability while working in the high fluence regime. Several years ago, this work began by collaborative works on some of the top class European EUV sources (including e.g. single stream gas-puff target EUV source at Laser-Laboratorium Göttingen, Germany (LLG) and double stream gas-puff target EUV source at Military University of Technology, Poland (MUT)), and by using them for several different applications (e.g. EUV ablation, EUV microscopy or near edge X-ray absorption fine structure (NEXAFS) spectroscopy). Recently, benchmark experiments have been performed at the HiLASE Centre in collaboration with the group of Dr. Mann (LLG), and by using the LLG gas-puff target coupled with the HiLASE picosecond Yb:YAG laser. On the basis of these activities, the effective parameters for the construction of the next generation of EUV plasma sources at the HiLASE Centre are presented. As stated above, the HiLASE experimental setup targets a wide range of possible applications in industry and in medicine, as well as in pure scientific research, like lithography and surface processing of polymers for fabrication of microchips or medical devices (increasing biocompatibility of plastic prostheses), as well as EUV microscopy with possible biological applications to spectroscopy and material characterization. In order to support precise manufacturing, monochromatic EUV radiation is required [Bakshi 2006], but for spectroscopy, broadband radiation with different optical schemes must not be excluded. Thus, an experimental setup based on the model of LLG EUV source is under construction. In order to understand the construction requirements for targeting such a wide range of applications, it is necessary to take a step back and look at the general concept of EUV sources and of the methods to deliver a EUV beam to the experiments. With EUV sources, the intermediate focus (IF) is where the EUV light is focused and is defined as the illuminator entrance. One positive, albeit peculiar, property of EUV sources comes directly from this fact: both the exposure tool and its illuminator are independent of the specific characteristics of the EUV source itself. In other words, the characteristics of the EUV light at the IF do not depend on the method of generating the plasma or on its material [Bakshi 2006]. This property is very important for the HiLASE Center as it allows the coupling of the EUV source with more lasers with different kind of properties [Smrz 2017]:  The cryogenically cooled Yb:YAG slab laser system Perla A- cryo, with 100 mJ energy in pulse, 100 Hz repetition rate and 450 ps pulse duration. With future upgrades, less than 10 picosecond duration and 1 J energy in pulse is expected.  The so called Perla A120 laser system with 120 mJ pulse energy, 1 kHz repetition rate and 1.4 ns pulse duration, with compressor being currently assembled, targeting few ps pulse duration.  The thin-disk laser system Perla B20 with less than 20 mJ of energy in pulse, 1 kHz repetition rate and less than 2 ps pulse duration. All the systems work at 1030 nm wavelength. One advantage of using more laser systems is the possibility to work in more different plasma regimes and therefore having the ability to generate plasma with a wide range of characteristics. Due to the different properties of the generated plasmas we will be able to produce EUV beams in two different wavelength ranges: 13.5 nm and in the water window range, 2.33-4.40 nm. The first wavelength is particularly suitable for EUV lithography [Bakshi 2006] and for high precision and high volume manufacturing, while the water window range is well known for its various application in biology [Wachulak 2015, Sedlmair 2012] (spanning from imaging to functionalization of materials). There are currently two main techniques used for generation of high power EUV radiation in a small laboratory but not a large scale facility [Bakshi 2006]: Laser produced plasma (LPP) and gas discharge produced plasma (DPP). The HiLASE EUV source will be a LPP source and it is important to remark that by considering only plasma sources, the applications area is not restricted. Indeed, several materials (N2, Xe, Sn, etc.), or a mixture of them [Bakshi 2006, Bartnik 2010, Duda 2018], can be used for plasma production. This means that there are many potential candidate target materials and consequentially the EUV source can be used for high-volume manufacturing (HVM) as well as for scientific research. It is important to note that these targets can be either liquid, gas or solid. Solid target provides most intense EUV light, but has intrinsic problem with debris production. Further, it must be put on a roto-translational stage, moving in helix, so that the laser ablates fresh areas of the target during the whole experiment. This movement creates some plasma instability, depending on the non-uniformity in the particular solid target surface ablated and/or in some discontinuity of the motion itself. Liquid targets are used together with CO2 lasers in HVM systems, but are unsuitable for driving lasers at 1 μm wavelength due to limited absorption [Bakshi 2006]. In this work, a single stream