PROCEEDINGS OF SPIE. Performance of one hundred watt HVM LPP-EUV source

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1 PROCEEDINGS OF SPIE SPIEDigitalLibrary.org/conference-proceedings-of-spie Performance of one hundred watt HVM LPP-EUV source Hakaru Mizoguchi, Hiroaki Nakarai, Tamotsu Abe, Krzysztof M Nowak, Yasufumi Kawasuji, et al.

2 Performance of one hundred watt HVM LPP-EUV Source Hakaru Mizoguchi, Hiroaki Nakarai, Tamotsu Abe, Krzysztof M Nowak, Yasufumi Kawasuji, Hiroshi Tanaka, Yukio Watanabe, Tsukasa Hori, Takeshi Kodama, Yutaka Shiraishi, Tatsuya Yanagida, Georg Soumagne, Tsuyoshi Yamada, Taku Yamazaki, Shinji Okazaki and Takashi Saitou Gigaphoton Inc. Hiratsuka facility: Shinomiya Hiratsuka Kanagawa, , JAPAN ABSTRACT We have been developing CO 2 -Sn-LPP EUV light source which is the most promising solution as the 13.5nm high power light source for HVM EUVL. Unique and original technologies such as: combination of pulsed CO 2 laser and Sn droplets, dual wavelength laser pulses shooting, and mitigation with magnetic field, have been developed in Gigaphoton Inc. The theoretical and experimental data have clearly showed the advantage of our proposed strategy. Based on these data we are developing first practical source for HVM: GL200E. This data means 250W EUV power will be able to realize around 20kW level pulsed CO 2 laser. We have reported engineering data from our recent test such around 43W average clean power, CE=2.0%, with 100kHz operation and other data 19). We have already finished preparation of higher average power CO 2 laser more than 20kW at output power cooperate with Mitsubishi Electric Corporation 14). Recently we achieved 92W with 50kHz, 50% duty cycle operation 20). We have reported component technology progress of EUV light source system. We report promising experimental data and result of simulation of magnetic mitigation system in Proto #1 system. We demonstrated several data with Proto #2 system: (1) emission data of 140W in burst under 70kHz 50% duty cycle during 10 minutes. (2) emission data of 118W in burst under 60kHz 70% duty cycle during 10 minutes. (3) emission data of 42W in burst under 20kHz 50% duty cycle (10000pls/0.5ms OFF) during 3 hours (110Mpls). Also we report construction of Pilot #1 system. Final target is week level operation with 250W EUV power with CE=4%, more than 27kW CO 2 laser power by the end of Q2 of Keywords: EUV light source, 13.5nm, LPP, CO 2 laser, Sn, Lithography, HVM 1. INTRODUCTION Extreme ultraviolet (EUV) light source has been being developed together with a scanning exposure tool. As the alpha-tool with 10 W EUV light source, ASML shipped alpha-demo tool in ) and Nikon shipped EUV-1 in ) The alpha-demo-tool of ASML was NXE-3100 in the beginning of 2011 with 100 W EUV light source. 3)4) The requirement of the EUV exposure tool development is now in the beta-tool (for high volume manufacturing (HVM)) stage. Several machines are already shipped in The required EUV power is 250 W clean power (after purifying infrared (IR) and deep ultra violet (DUV) spectra) at intermediate focus (IF). Unfortunately demonstrated power level is still around 50W. Since 2002, we have been developing the carbon dioxide (CO 2 ) laser produced thin (Sn) plasma (CO 2 -Sn-LPP) EUV light source which is the most promising solution as the 13.5 nm high power (>200 W) light source for HVM EUV lithography (EUVL). 5)6)7) We have chosen the LPP-EUV method because of its high efficiency, power scalability, and spatial freedom around plasma. Our group has proposed several unique original technologies. The theoretical 8) and experimental 9) data have clearly demonstrated, combination of CO 2 laser and Sn plasma realize high conversion efficiency (CE) from driver laser pulse energy to 13.5nm EUV 2% in-band energy. In 2012 we have demonstrated this experiment shoed the advantage of combining a laser beam at a wavelength of the CO 2 laser system with Sn plasma to achieve high CE>4.7% (in maximum) from driver laser pulse energy to EUV in-band energy 1) in small size (2Hz) experimental device. We have been developing extension of high CE operation condition at 100kHz range, technical challenge are very stable droplet generation, very stable laser beam performance and high accuracy shooting control. Simultaneously the other Extreme Ultraviolet (EUV) Lithography VI, edited by Obert R. Wood II, Eric M. Panning, Proc. of SPIE Vol. 9422, 94220C 2015 SPIE CCC code: X/15/$18 doi: / Proc. of SPIE Vol C-1

3 challenges include the requirements for high average power, and superior beam quality of CO 2 laser 10) which is based on commercial high average power cw-co 2 amplifiers. We have finished preparation of higher average power CO2 laser more than 20kW at output power cooperate with Mitsubishi electric cooperation 2) 3). Fig.1 shows recent history of our progress. Last year we reported 43W operation data in this conference 19), 92W operation data in EUVL workshop 20). In this paper we introduce progress of each key-components technology and update the system operation data. In October 2014, we achieved 118W with 60kHz, 70% duty cycle operation 21). The latest improvements are reported at more than one hundred watt stable operation under 4% CE with 20 micron droplet and magnetic mitigation. R t$ a g o 1-8W (2013.2) 'st A EUV power status 250W Pilot target 4_ 1 I Consistent results have been demonstrated for the last 9 quarters W Next target 4-118W ( ) A F 92W (2014.6) 1 I I 43W (2014.2) 4-15W (2013.8) GPI development Fig.1 Progress of EUV power ( Gigaphoton development) 2. LPP EUV LIGHT SOURCE CONCEPT AND COMPONENT TECHNOLOGIES Sn droplet target supply,- Plasma guiding / magnet IF Collector mirror Fig. 2 The concept of Gigaphoton HVM EUV light source At first step Sn droplet target is irradiated with pre-pulse laser. The Sn droplet is crushed to sub-micron mists. The mists are expanded in time. At second step after certain delay time the mists cloud is expanded and heated by pulsed CO 2 laser beam. The cloud is converted to high temperature plasma. Sn ions have several number of charges. During recombination process Sn plasma emits 13.5nm EUV light. Most of the Sn ions can be trapped by the Proc. of SPIE Vol C-2

4 magnetic field by Larmor movement. To prevent the collector mirror from being contaminated, Sn plasma needs to be trapped before being deposited on the collector mirror. Residues of the plasma after emitting EUV light are eventually scattered inside the vessel. To enhance EUV energy and to maximize Sn debris mitigation, number of Sn ions should be maximized in these laser heating processes. 2.1 Pre-pulse technology 11)12)13) The Sn fragments are generated after the pre-pulse irradiation. The diameter of the fragments reaches less than few micrometers at the maximum. The Sn fragments are measured by a shadowgraph method with a few nanosecond pulsed back illuminator and a CCD camera with a high-resolution telescope. Fig. 3 shows the shadowgraphs of the fragments after the pre-pulse laser irradiation on the 20 µm diameter droplet. The droplet is irradiated with the pre-pulse laser from left hand side in the image. to opposite ofef pre guise plasma expansion. Liquid de formation speed ' - towms (Same speed( Fig.3 Shadowgraph of fragments after pre-pulse irradiation with 10ns pulse and 10ps pulse, and modeling. In case of 10ns pre-pulse laser irradiation, the cloud fragments are moved to the opposite side while expanding in diameter. On the other hand in case of 10ps pre-pulse irradiation, cloud of fragments are expanded all of direction. This phenomena is explainable with difference of pre-pulse expansion mechanism of ns-pulse and ps-pulse. The mechanism of difference is shown in Fig.3. CO2 pulse enegy vs. EUV -CE Pre-pulse laser X10 ps X10 ns CO2 laser pulse energy (mj) Fig.4 Conversion efficiency dependence between 10ns and 10ps pre-pulse Proc. of SPIE Vol C-3

5 The pre-pulse laser condition is a key parameter for obtaining higher CE. The CE reached 3.3 % with the 20 µm droplet by optimizing the 10ns pre-pulse laser conditions. On the other hand, the CE reached 4.7 % with the 20 µm droplet by optimizing the 10ps pre-pulse laser conditions (Fig.4). This high CE technology enables 250W EUV source with 20kW CO 2 laser. EUV light is emitted from the Sn plasma, which is mainly composed of Sn ions. Therefore ionization rate is essential parameter to obtain higher CE. The distribution of the Sn neutral atom density after the pre-pulse laser irradiation in a certain magnetic field were observed with the Laser Induced Fluorescence (LIF) method. The Sn atoms are excited by the transition of 5p 2 3 P 0 6s 3 P o 1 (286.3 nm). The fluorescence from the transition of 5p 2 3 P 2 6s 3 P o 1 (317.5 nm) is observed with an image intensified CCD camera through a band-pass filter. The calculated ionization ratio vs. CO 2 laser energy is shown in Fig.5. Also CE vs. CO 2 laser energy is shown in Fig.6. In both figure pulse duration of pre-pulse are experimental parameter respectively. In case of 10ns pre-pulse Ionization ratio changes with CO 2 laser pulse energy, as shown in Fig.5. This data indicates that when CO 2 laser energy is above a certain energy level, almost all the Sn atoms in the Sn droplet are ionized. On the other hand, in case of 10ps pre-pulse ionization rate is very high even in case of low CO 2 pulse energy. This is a very good indication, because this means that Sn ionization rate keeps high level even under low CO 2 irradiation energy. The debris mitigation system also works under low power operation. loniation performance 1-z source data CE performance 100% 80% Z\ N ß 60% l0 'E 40% 0 20% Proto performance Proto performance 0% CO2 pulse energy on droplet Itns -pulse laser -1.-ps -pulse laser Fig.5 Ionization ratio vs. CO 2 laser energy CO2 pulse energy (mj) -- ns -pulse laser -a-- ps -pulse laser 1 Fig.6 CE vs. CO 2 laser energy 2.2 Droplet generation and Magnetic mitigation technology Fig.7 Schematic of collector mirror and mitigation system Proc. of SPIE Vol C-4

6 Our Sn debris mitigation concept with the magnetic field is shown in Fig.7. Because EUV light is emitted from the Sn plasma, which is mainly composed of Sn ions and electron, almost all the Sn ions can be trapped in the strong magnetic field. Therefore, the maximization of ionized Sn ion ratio is essentially important from the point of conversion efficiency, and also mitigation of Sn. If all the Sn atoms are ionized, all the Sn ions can possibly be guided along the magnetic flux. Also, some neutral atoms can be guided and trapped by charge exchange with ions. 11) This system is also equipped with a chemical etching mechanism. With this etching mechanism the remaining Sn atoms are removed from the surface of the collector mirror and of some view ports. 12) The main function of the EUV vessel is to maintain high level vacuum environment around EUV plasma and to mechanically position the components, such as the collector mirror and the droplet generator and so on. The EUV vessel schematic is shown in Fig.7. It contain 7 components; one droplet generator, one droplet catcher, one collector mirror, a pair of super-conductive magnet and a pair of ion collector. In order to mitigate Sn debris, a pair of superconductive magnetic coils is co-axially aligned both side of the vessel. One of the most important requirements is to fully capture Sn atoms after EUV radiation for the extension of the lifetime of the collector mirror. Sn deposition of even 1 nm thick layer on the EUV collector mirror, i.e. a few atomic layers, degrades the mirror reflectivity by 10 %, which needs to be taken into consideration in the mirror lifetime specification. 12) The supplied Sn has to be almost fully removed from the active region in order to prevent deposition (evaporated material, molten droplets, slow ions), erosion (fast ions), and implantation (ultra fast ions) on the collector mirror. 2-3 Droplet generator The small Sn droplet generation is particularly important in Sn debris mitigation. The mass of Sn should be minimized to what is necessary to obtain EUV photons, to minimize Sn debris. The Sn supply tank is heated above the melting temperature of Sn (> degree Celsius). The liquid Sn droplets are generated from the droplet generator. The long term positional stability of the droplets is indispensable to maintain the long term EUV IF power stability. The droplet position is measured by a position sensor and the results are fed back to the droplet generator stage. This is very important because the droplet position determines the EUV light source position. Also pre-pulse laser and CO 2 laser irradiation positions are monitored, which, combined with monitoring of the droplet position, enables to stabilize CE and EUV light source position and to improve Sn debris mitigation, and is extremely important for commercial use. The EUV light source system is equipped with droplet position sensors and controllers; it also has pre-pulse laser and CO 2 laser position controllers to stabilize plasma position and the EUV energy. Recently we succeeded to realize stable 20um droplet generation. The droplet generator is shown red rod and the droplet catcher is shown bleu rod in Fig CO 2 driver laser system The pulsed Master Oscillator Power Amplifier (MOPA) CO 2 laser system has 20 nsec pulse duration (FWHM) and 20 kw average output power at 100 khz repetition rate, which are optimized for Sn plasma generation. The hybrid CO 2 laser system consists of a short-pulse highrepetition-rate master oscillator (master-osc) and multistage cascade amplifiers. The master-osc laser is a Q- switched, 20 nsec, single P(20) line, RF-pumped waveguide CO 2 laser. The RF-excitation is a commonly employed scheme in axial flow or diffusion cooled slab or waveguide configurations, allowing a high repetition rate in pulsed operation by a well designed amplification system, for high repetition rate plasma generation. The commercial cw-co 2 amplifiers are used as the amplifiers with some modifications. The laser system is operable from low duty mode (2 %) to full duty mode (100 %). The targeted specifications of this laser system are Fig.8 Driver CO 2 laser system test at Mitsubishi electric Proc. of SPIE Vol C-5

7 - following; The master-osc generates pulses at the repetition rate of 100 khz, with 20 nsec pulse duration, and with 150 W (1.5 mj, 100 khz) power 17). The OSC contains two major parts. One is master-osc that oscillates a pulse, and the other one is OSC-AMP that amplifies the pulse energy. The pre-amplifier (pre-amp) amplifies the pulse from 150 W to around 3.0 kw (30 mj, 100 khz) output level with a slab-type discharge chamber. The mainamplifiers (main-amp) further amplify the pulse from 3.0 kw to 20 kw (200 mj, 100 khz) output level with three sets of CW discharge CO 2 laser systems.since 2011 we have develop new CO 2 laser amplifier co-operate with Mitsubishi electric supported by NEDO 14)16). In 2013 we succeeded to demonstrate 21kW output power with engineering test stand1 15)16)17). 2-5 IR reduction technology on collector mirror 18) After EUV plasma is created, EUV light is collected by multilayer mirror. However EUV plasma emits not only EUV light, but also UV light, visible light and infrared light respectively. These light components are called Out of band light (Fig.9(a)). In past, several kind of filter is used to cut these out of band components. However filter is heated up by absorption of filter material itself. We have innovated new type filter; there has grating like structure on the surface of multilayer. Reflected IR light from the multilayer makes interference pattern at focal plane (patent pending). Only IR light is absorbed by aperture stop. Fig.9 (b) shows the schematic of this new filter. Fig. 10 shows the measurement results of the new type out of band filter. The data shows quite high transmittance (around 45%) of this filter at all of distance from central axis of mirror 18) v % c Wavelength, nm Fig.9 (a) Out of Band spectrum IR Light EUV Light. 10 Wm Wan, Laser EapaMerJ CMpprr I val (b) Schematic of new type filter EN Reflectivity IR Reflectivity V5- E % M4.wi"atmrvlcn VS- loviam,vwyn V5- E % le 1.14 SO Fig.10 Measurement result of (a) Reflectivity at radial position, (b) Interference pattern on focal plane 18). Proc. of SPIE Vol C-6

8 3. SYSTEM TEST AND RESULT To realize our EUV light source, we are constructed two proto type unit; proto #1 and #2. The configuration and target specification of each proto type device is shown in Table 1. Major difference between three systems is CO 2 laser power and output angle, other specification is essentially same. Pilot system is under planning at this moment. Table 1 shows configuration and target specification of two Prototypes and Pilot systems. Table 1 Specification of 3 devices of Gigaphoton Operational Specification Proto # I Proto #2 Pilot EUV Power 25 W 100 W 250 W CE 3% 4% 4% Pulse rate 100 khz 100 khz 100 khz Target Performance Output angle Horizontal 62' upper (matched to NXE) 62 upper (matched to NXE) Availability 1 week operation 1 week operation > 75% Droplet generator CO2 laser m >8kW 20 um >12kW <20Itm 25 kw Technology Pre -pulse laser picosecond picosecond picosecond Debris mitigation validation of magnetic mitigation in system 10 days >30 15 days days 3-1 Proto type #1 system We have been develop system technology and component test at proto #1 since ). In 2012, we concentrate to solve two issues, one is dramatic improvement of long-term stability of droplet generator, the other is CO 2 laser power from 5kW to 9kW. We observed 34W EUV emission at proto #1 device with step by step approach. Fig.11 Pilot #1 system Proc. of SPIE Vol C-7

9 Fig.12 Deposition on the C1 mirror a) simulation b) actual picture Fig.12 shows thin deposition on the C1 mirror after 3 days operation in proto #1. Also thin deposition simulation result is shown. From this simulation the root cause of the deposition is estimated, it is reverse diffusion of thin from ion catcher. Therefore we are now improving this diffusion by re-design of ion catcher with 3 steps. Fig.13 shows the expected result of improvement by the simulation. We believe this magnetic mitigation approach is promising from these experiment and simulation. Ì= Fig. 13 Improvement of deposition from ion catcher (simulation) 3-2 Proto type #2 system Fig.14 EUV chamber of proto #2 system Proc. of SPIE Vol C-8

10 We have started the construction of proto #2 system in 2H of The operation has started beginning of The picture of EUV chamber is shown in Fig14. EUV chamber is compatible to EUV tool. The chamber is builded between pair of super conductive magnet. Tubing and wire are flexibly connected to the EUV chamber for ease of maintenance. For further power scale-up, not only higher CE development, but also higher power driver laser development is essentially important. We have done the CO 2 laser driver pre-amplifier improvement; slab type pre-amplifier is replaced by new pre-amplifier made from Mitsubishi Electric. Driver CO 2 laser of Proto #2 system is enhanced from 8kW to 20kW. This 20kW output power corresponds 14 kw at the plasma point because of transmission loss of CO 2 laser optics. Fig.15 shows picture of this new pre-amplifier laser installation in our laboratory. Typical output data of new CO 2 laser driver system is shown in Fig.16. Blue line shows data of old laser system, its maximum power limited around 10kW by self oscillaton. However power was enhanced up to 20kW after the replacement of pre-amplifier. Also typical pulse waveform 11.7ns (FWHM) and beam profile are shown. 1 4./ Fig.15 New CO 2 laser pre-amplifier ( Produced by Mitsubishi electric) for 20kW CO 2 laser system. Proto#2 performance Pulse waveform Beam Profile o Input (W) -.-Rofin PA --Mitsubishi PA(26A) Fig.16 Input / Output power and temporal / spacial ptofile of CO 2 driver laser system of proto #2 Proc. of SPIE Vol C-9

11 3-3 Latest experimental result of Proto #2 system Emission data of EUV is shown in Fig.17 shows 140W in burst under 70kHz 50% duty cycle. This operation realized 70W average ( 140Wx50%) output power during 10 minutes.. Fig.18 shows 118W in burst under 60kHz 70% duty cycle. This operation realized 83W average ( 118Wx70%) output power during 10 minutes.fig.19 It shows 42W in burst under 20kHz 50% duty cycle (10000pls/0.5ms OFF). This operation realized 21W average ( 42W x 50%) output power during 3hours (110Mpls). Data (a) shows EUV energy trend during 3 hours, and data (b) shows spatial stability of droplet at the shooing point. These data shows stable operation has achieved during 3 hours. Next target of proto #2 is week level operation with over 100W EUV power with 14kW CO 2 laser power % duty o Fig.17 EUV 140W in burst (70W average) power data 140 EUV dean power 10 Pulse data in burst a, 0.4sec ON, 0.167sec OFF _ Burst number nu, 11.11, V M law valu number Fig.18 EUV 118W in burst (83W average) power data Fig.19 EUV 42 W in burst (a) energy stability and (b) droplet stability at shooting point during 3 hours. Proc. of SPIE Vol C-10

12 3-4 Pilot #1 system Fig W LPP EUV Light Source System (Pilot #1) Structure of Pilot #1 EUV source is shown in Fig.20. To minimize optical loss of EUV light the EUV vessel is connected to the scanner tightly. To minimize overall footprint in the clean room area, the CO 2 laser system is located on a different floor (usually downstairs) from where the scanner is located (Fig.21). CO 2 driver laser system configuration between device is shown in Fig.17. This pilot #1 system facilitate full Mitsubishi CO 2 laser amplifier. Estimated maximum power at the laser exit is 27kW and power at the plasma point is 20kW (Fig.22). Final target is week level operation with 250W EUV power with CE=4%, more than 27kW CO 2 laser power by the end of Q2 of _tom -1 Fig.21 Structure of CO 2 driver laser system in Pilot #1 system Target at Plasma SkW 8kw 14kW System Endurance Testing Platform IPower Up Testing Power Up Testing Oscillctor Pre Amplifier Main Amplifier GPI R T T Pilot It Fig.22 CO 2 driver laser system configuration of Proto #1, #2 and Pilot #1 Proc. of SPIE Vol C-11

13 4. CONCLUSION - We have reported component technology progress of EUV light source system. - We reported promising experimental data and result of simulation of magnetic mitigation system in Proto #1 system. - We demonstrated following data with Proto#2 system; (1) Emission data of 140W in burst under 70kHz 50% duty cycle during 10 minutes. (2) Emission data of 118W in burst under 60kHz 70% duty cycle during 10 minutes. (3) Emission data of 42W in burst under 20kHz 50% duty cycle (10000pls/0.5ms OFF)during 3hours. Next target of proto #2 is week level operation with over 100W EUV power with 14kW CO 2 laser power. - We report construction of Pilot #1 system. Final target is week level operation with 250W EUV power with CE=4%, more than 27kW CO 2 laser power by the end of Q2 of Finally as summary, we show the milestone of our development in Table 2. Table 2 Milestone of EUV light source development This work 140W 2014,04 > 14kW >4.2% 26.7% Mitsubishi pre. amp :Proto #2 Grating Type Pilot #1 250W 2015,02 > 20kW > 4.5% 26.7% Mitsubishi main amp. system Grating Type 5. ACKNOWLEDGMENT This work was partly supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan. We acknowledge their continuous support. We acknowledge to following researchers and organizations; Plasma simulation is supported by Dr. Jun Sunahara, Dr. Katsunori Nishihara, Prof. Hiroaki Nishimura, and others in Osaka University. Plasma diagnostics is supported by Dr. Kentaro Tomita, Prof. Kiichiro Uchino and others in Kyushu University. Laser engineering is supported by Dr. Akira Endo :HiLase Project (Prague) and Prof. Masakazu Washio and others in Waseda University. We also acknowledge Mitsubishi Electric CO 2 laser amp. develop. team: Dr. Yoichi Tanino, Dr. Junichi Nishimae, Dr. Shuichi Fujikawa and others. Authors are very sorry to miss Dr. Yoichi Tanino in Mitsubishi Electric Corporation with sudden death on 1 st February in We appreciate his extreme great job of CO 2 amplifier development in very short period and pray for the soul of him. Proc. of SPIE Vol C-12

14 REFERENCES [1] Noreen Harned, et. al.: EUV lithography with the Alpha Demo Tools: status and challenges, Proc. SPIE 6517 (2007) [ ] [2] Takaharu Miura et. al.,: Nikon EUVL development progress update Proc. SPIE 6921 (2008) [6921-0M] [3] Christian Wagner, et. al.: EUV into production with ASML's NXE platform, Proc. SPIE 7636 (2010) [7636-1H] [4] Christian Wagner, et. al.: Performance validation of ASML s NXE:3100, Proc. SPIE 7969 (2011) [ ] [5] Hakaru Mizoguchi, et. al.: First generation laser-produced plasma source system for HVM EUV lithography, Proc. SPIE 7636, (2010) [ ] [6] Akira Endo, et. al.: Laser produced EUV light source development for HVM, Proc. SPIE 6517 (2007) [7] Hakaru Mizoguchi, et. al.: 100W 1 st Generation Laser-Produced Plasma light source system for HVM EUV lithography, Proc. SPIE 7969 (2011) [796908] [8] K. Nishihara, et. al., EUV Sources for Lithography, Chap. 11, ed. V. Bakshi, SPIE, Bellingham, [9] H. Tanaka, et. al.: Comparative study on emission characteristics of extreme ultraviolet radiation from CO 2 and Nd:YAG laser-produced tin plasmas, Appl. Phys. Lett. 87, (2005) [10] H. Hoshino, et. al.: LPP EUV light source employing high-power CO 2 laser, Proc. SPIE 6921 (2008) [11] Tatsuya Yanagida, et. al.: Characterization and optimization of tin particle mitigation and EUV conversion efficiency in a laser produced plasma EUV light source, Proc. SPIE 7969 (2011) [ ] [12] Junichi Fujimoto, et. al.: Development of the reliable 20 kw class pulsed carbon dioxide laser system for LPP EUV light source, Proc. SPIE 7969 (2011) [ ] [13] Hakaru Mizoguchi: High CE technology for HVM EUV source (EUV Symposium 2012, Oct , Brussel) [14] Yoichi Tanino: A proposal for an EUV light source using transverse flow CO 2 lasers (EUV Symposium 2 012, Oct , Brussel) [15] Hakaru Mizoguchi et al: High Ce and Magnetic Mitigation Technology for HVM EUV Source (EUV Symposium 2013, Oct , Toyama) [16] Yoichi Tanino et.al.: A Driver CO 2 Laser Using Transverse-flow CO 2 Laser Amplifiers (EUV Symposium 2013, Oct , Toyama) [17] Krzysztof M Nowak, Yoichi Tanino et.al.: EUV driver CO 2 laser system using multi-line nano-second pulse high-stability master oscillator for Gigaphoton's EUV LPP system (EUV Symposium 2013, Oct , Toyama) [18] RIGAKU technical display: IR Rejection Collector Optic Manufacturing Process (EUV Symposium 2013, Oct ,Toyama) [19] Hakaru Mizoguchi, et. al.: Sub-hundred Watt operation demonstration of HVM LPP-EUV source, Proc. SPIE 9048, (2014) [ ] [20] H. Mizoguchi et. al.: One hundred Watt Operation Demonstration of HVM LPP-EUV Source, 2014 EUVL workshop (2014. Jun , Maui, USA) [21] H. Mizoguchi et.al.: Performance of One-Hundred Watt HVM LPP-EUV Source, 2014 EUVL Symposium (2014. Oct , Washington D.C., USA) Proc. of SPIE Vol C-13