Progress in LPP EUV Source Development by Japan MEXT Project Y. Izawa, N. Miyanaga, H. Nishimura, S. Fujioka, T. Aota, K. Nagai, T. Norimatsu,K. Nishihara, M. Murakami, Y. -G. Kang, M. Nakatsuka, H. Fujita, K. Tsubakimoto, H. Yoshida, K. Mima ( ILE, Osaka University) S. Uchida, Y. Shimada, M. Yamaura, K. Hashimoto, A. Sunahara, H. Furukawa (Institute for Laser Technology) F. Koike (Kitazato University) H. Tanuma (Tokyo Metropolitan University) T. Kawamura (Tokyo Institute of Technology) K. Fujima (Yamanashi University) R. More, T. Kato (National Institute of Fusion Science) A. Sasaki (Advanced Photon Research Center, JAERI) T. Kagawa (Nara Womens College) T. Nishikawa (Okayama University) 4thEUVL Symposium November 7-9, 2005 San Diego, USA
Basic research on EUV plasma is important. MEXT project (2003-2007) Collaboration Objectives 1) Understanding physics of EUV source plasma and providing guidelines for practical EUV source design High power and high efficiency EUV data base (experiments and simulations) Optimization of EUV plasma (laser and target) Clean, debris free source (H. Nishimura et al.) Data base on ion and neutral atom emission Suppression of high energy ions 2) Development of new targets (K. Nagai et al.) low density, mass-limited, high feed rate METI project (2002-2007) 3) Development of laser technology 5 kw/5 khz DPSSL compact, high efficiency, good beam quality, long life Objectives: EUVL system R&D MEXT: Ministry of Education, Culture, Science and Technology METI; Ministry of Economy, Trade and Industry 2
Guideline for optimization of EUV source Design windows EUV power : 300W at source @ - 30kHz Large size plasma: 400 ~ 700 mm Low laser intensity: 11 ~ 12 W/cm 2 Low electron density: 19 ~ 21 cm -3 Electron temperature: 20 ~ 40 ev 4 2 Low density foam target may be a powerful candidate. gas jet target discharge plasma foam target Opacity for EUV emission will be important. Selection of laser wavelength and pulse width. 1 solid target 16 20 22 18 plasma scale length (mm) 00 0.6 mm t = L 20 optically too thin optimum density-depth product 5 2 1.06 mm0.53 mm0.25 mm 20ns ns 5ns optically too thick 5 2ns 1ns 5 2 1 2 1 etendue limit 1mm 2 sr (W=p) 17 18 19 20 ion number density (cm -3 ) 3
Research flow to high power and efficient EUV source Atomic data By CXS Xe 11+ Xe + Transmission 1.2 1.0 0.8 0.6 0.4 T e ~ 30 ev Sn Benchmark Atomic model Radiation hydro code Benchmark EUV experiment Laser: I, t, l Target: Z, r, Intensity Intensity 4d-4f Simulation 4d-5p Xe + Xe 9+ 1x 11 W/cm 2 1x 12 W/cm 2 Experiment 0.9x 11 W/cm 2 0.9x 12 W/cm 2 Xe 9+ By HULLAC Code 8 12 14 16 18 wavelength (nm) wavelength (nm) 0.2 0.0 8 Conversion efficiency (%) T e ~ 0 ev 12 14 16 18 Wavelength (nm) Experiment Simulation Laser intensity (W/cm 2 ) Electron temperature(ev) Conversion efficiency Ion density (/cm 3 ) Design of high power and clean EUV source 4
Radiation hydrodynamic simulation reproduces well the measured spectra. Radiation spectra drastically changes with laser intensity. Target: Sn, laser wavelength: 64 nm Sn 8.8x [W/cm 2 ] Exp. 11 5 1x 11 [W/cm 2 ] Sim. Intensity (a.u.) 3.0x 11 [W/cm 2 ] 9.0x 11 [W/cm 2 ] 5 9 2 2x 11 [W/cm 2 ] 1.5 5 9 3 1.0x 12 [W/cm 2 ] 2 0 5 15 20 Wavelength (nm) 0 0 5 15 20 Wavelength (nm) 5
Mapping of conversion efficiency by power balance model electron temperature [ev] Sn: short pulse laser (< 5 ns) Xe, Li: long pulse laser (> 5 ns) 80 Sn 2ns 50 30 20 17 18 19 20 ion density [cm -3 ] 80 80 For Sn, high conversion is obtained for a wide range of n i and T e Te [ev] 50 50 30 30 20 20 Li 30ns 80 50 30 20 Xe 15ns 17 18 19 20 ion density [cm -3 ] 17 17 18 18 19 19 20 20 ion density [cm -3 ] 6
EUV plasma diagnostics ion (Thomson parabola) neutral particle (LIF) x l x t 7
Experimental results were compared with simulation. 0.53-µm (2w) probe 0.27-µm (4w) probe Distance from target surface (µm) 0 0 200 300 400 500 - -5 0 5 15 Time (ns) 150 µm 12.2 ns Laser pulse ( ns) Spatially integrated temporal profile 220 µm Ion number density (cm-3 Electron temperature (ev) Degree of ionization Time integrated spatial profile Experimental condition Laser wavelength: 1.064mm I = 1 11 W/cm 2 Target: Sn stripe 1x 11 W/cm 2 Position (µm) 8
EUV spectral shape depends on laser wavelength and pulse width. Short wavelength Long pulse Increase in ion density Increase in scale length Increase in opacity, and spectral dip at 13.5 nm Nomalized intensity (arb. units) Intensity normalized at 13.5 nm 120 0 80 60 40 20 Sn 1.06mm 12 14 16 Wavelength (nm) EUV spectrum (3 ns) EUV spectrum ( ns) 5 x W/cm 2 18 20 relative intensity (a.u.) 1.2 1 0.8 0.6 0.4 0.2 Sn 1.06mm 0.53mm 0.27mm 5 x W/cm 2 0 8 12 14 16 18 20 wavelength (nm) 9
EUV spectral shape depends on initial mass-density. Opacity can be controlled by target initial mass-density. SnO 2 foam target Intensity normaized by laser intensity 350 300 250 200 150 0 50 Laser wavelength: 1.06 µm (5.2±0.7)x W/cm 2 Improved spectral purity 2.9x W/cm 2 Intensity normaized by laser intensity 350 300 250 200 150 0 50 Laser wavelength: 0.53 µm (4.2±0.2)x W/cm 2 Improved efficiency 0 8 12 14 16 18 20 Wavelength (nm) 0 8 12 14 16 18 20 Wavelength (nm)
Conversion efficiency is improved by controlling target mass-density and laser pulse width. Nd:YAG [64 nm, 2-3 ns/ns] Nd:YAG [64 nm, ns] 2.5 Conversion efficiency (%) 2.0 1.5 1.0 0.5 0.0 2 ~ 3 ns 1.2 ns ns 8 ~ ns Simulation 2 3 4 5 6 7 11 2 3 4 5 6 7 12 2 Laser intensity (W/cm 2 ) CE (%/2 sr/2%bw) Laser intensity (x W/cm 2 ) 11
Summary Guideline to achieve high conversion from laser to EUV radiation has been established by the experiments and simulation. For Sn plasma, opacity effect is important, and short pulse laser and low density target will be effective for high efficiency. High conversion efficiency was achieved. Sn: 3 % (spherical plasma), SnO 2 foam: 2.5 %, Xe (solid): 1.1 %, Li: > 1% 5kHz/5kW laser has been developed, and will be used for high power EUV experiment in this year. 12