2008 International Workshop on EUV Lithography Efficient EUV source by use of a micro-target containing tin nanoparticles Takeshi Higashiguchi higashi@cc.utsunomiya-u.ac.jp Utsunomiya University, Japan Masanori Kaku, Masahito Katto, and Shoichi Kubodera University of Miyazaki, JAPAN 10-12 June 2008 (Wailea Beach Marriott, Maui, Hawaii, USA) Work supported by MEXT (Ministry of Education, Culture, Science and Technology, Japan) under contract subject Leading project for EUV lithography source development
Introduction A 10-ns Nd:YAG laser-produced Sn plasma Production of an efficient EUV emission Intensity (arb. units) 1.2 1 0.8 0.6 0.4 0.2 EUV CE ~ 1.2% (13.5 nm, 2%BW, cos 0.5 θ distribution) 0 9 101112131415161718 Wavelength (nm) T. Higashiguchi et al., RSI 76, 126102 (2005).
Liquid Sn jet target EUV CE of 2% from a YAG LPP T. Higashiguchi et al., RSI 78, 036106 (2007).
Use of low-density targets What kind of targets for Nd:YAG-Sn-LPPs? Possibility of low-density targets for efficient EUV emission 2.2% CE Osaka University (Japan) T. Okuno et al., APL 88, 161501 (2006). University College Dublin (Ireland) P. Hayden et al., JAP 99, 093302 (2006).
Introduction A 10-ns Nd:YAG laser-produced Sn plasma Micro-order debris emission was unavoidable with a solid target. θ = 20 100 μm T. Higashiguchi et al., RSI 76, 126102 (2005).
Low-debris, efficient CO 2 LPP using Sn target at EUVA EUV source coupled with 1-T magnetic field TEM cross sectional image Before exposure B = 0 Tesla B = 1 Tesla Y. Ueno et al., APL 91, 231501 (2007). Y. Ueno et al., APL 92, 211503 (2008).
Proposition How is use of a target for a LPP EUV source? Achievement of a low-debris & efficient EUV source Efficient EUV emission, EUV CE (> 1%) Tin (Sn) Reduce μm-neutral fragment particles Low debris High repetition rate operation Nanoparticle (6 nm av.) Low concentration (< 20%wt) Quasi-mass-limited microjet Regenerative liquid-jet target A regenerative liquid microjet target containing low-concentration tin (Sn) nanoparticles T. Higashiguchi et al., APL 88, 201503 (2006).
Objective We investigate various characteristics of a low- density colloidal jet target containing Sn nano particles and answer the following questions. Can we obtain a nominal EUV CE by use of a low-density colloidal target? Is the amount of debris really reduced with such a target?
Single laser pulse irradiation Schematic diagram of experimental setup Regenerative liquid microjet target containing tin nanoparticles EUV energy meter (Mo/Si mirror) Tank ω 10 ns Lens Single laser pulse (10 Hz) f = 30 cm XRD Microjet target (50 μm, <20%wt) LPP Differential pumping Spectrometer (1200 lines/mm) Pumping outlet Tank
Single laser pulse irradiation EUV spectra Enhancement of EUV emission with increase of concentration Intensity (arb. units) 4000 3000 2000 1000 O 5+ (4p-2s) O 5+ (4d-2p) O 5+ (3p-2s) O 5+ (3d-2p) 0 9 101112131415161718 Wavelength (nm) 17%wt 6%wt T. Higashiguchi et al., Proc. SPIE 6151, 615145 (2006).
Single laser pulse irradiation Concentration dependence of EUV CE Increase of EUV CE with increase of concentration 0.8 13.5 nm, 2%BW, 2π sr EUV CE (%) 0.6 0.4 0.2 0 0 5 10 15 20 Tin (Sn) concentration (%wt) T. Higashiguchi et al., Proc. SPIE 6151, 615145 (2006).
Use of dual laser pulses for compensation of EUV CE Schematic diagram of experimental setup Regenerative liquid microjet target containing tin nanoparticles Tank EUV energy meter (Mo/Si mirror) Lens Prepulse ω 2ω 10 ns 8 ns Dual laser pulses (10 Hz) f = 30 cm XRD Microjet target (50 μm, 6%wt) LPP Differential pumping Spectrometer (1200 lines/mm) Pumping outlet Tank
Use of dual laser pulses for compensation of EUV CE Enhancement of EUV CE at SnO 2 concentration of 6%wt 1.5 EUV CE (%) 1 0.5 0-200 0 200 400 600 Pulse separation time (ns) T. Higashiguchi et al., APL 88, 201503 (2006).
Use of dual laser pulses for compensation of EUV CE Optimum delay time explained by the plasma expansion (simpler estimate) τ crit n n e0 crit 1/ 3 r v Jet Exp 80 ns
Use of dual laser pulses for compensation of EUV CE Enhancement of EUV CE with increase of SnO 2 concentration in a target EUV CE (%) 2.5 2 1.5 1 0.5 17%wt 6%wt 0 0 1 2 3 4 Laser intensity (x10 11 W/cm 2 ) T. Higashiguchi et al., Proc. SPIE 6151, 615145 (2006).
Dual laser pulse irradiation at an optimum CE condition Suppression of ionic debris using dual pulses Comparison of energy spectra ESA signal (arb. units) without a pre-plasma 15 10 5 O + O 2+ Sn + Sn 2+ 0 0 5 10 15 20 Kinetic energy (kev) 15 10 5 with a pre-plasma Δτ = 100 ns 0 0 5 10 15 20 Kinetic energy (kev) T. Higashiguchi et al., APL 91, 151503 (2007).
Dual laser pulse irradiation at an optimum CE condition Comparison of XPS spectra before and after laser irradiation O1s After laser irradiation Before laser irradiation Intensity (arb. units) 15000 10000 5000 0 600 O1s Sn 3d C1s Si 2p Si 2s C1s Si 2s Si 2p O2s 500 400 300 200 100 0 Binding energy (ev) O2s M. Kaku et al., APL 92, 181503 (2008).
Dual laser pulse irradiation at an optimum CE condition Deposited rate Debris thickness (nm) 3 2 1 Single pulse Dual pulses 0 0 10000 20000 30000 40000 Number of laser pulses 0.3 nm/10,000 shots@model 0.7 nm/10,000 shots@experiment M. Kaku et al., APL 92, 181503 (2008).
Dual laser pulse irradiation at an optimum CE condition Reduction of deposited debris M. Kaku et al., APL 92, 181503 (2008).
One of the next generation EUV sources Coherent EUV sources Inverse Compton scattering High-order harmonic Using ion channel H. Kapteyn et al., Science 302, 95 (2003).
One of the next generation EUV sources Plasma channel of a capillary DPP waveguide 160 ns 250 μm 0 2 4 6 8 ne(10 17 cm -3 ) Discharge ON (160 ns) Discharge OFF
Summary We investigated various emission and debris characteristics of a low-density colloidal jet target containing tin nano particles. We were successful to increase the CE more than 1% even with a low-density colloidal target with a help of a pre-plasma. The amount of ionic debris significantly decreased when the optimum CE conditions were fulfilled simultaneously. The deposited amount of debris, however, seemed to be no change even using double laser pulses. We shows the potential of the target, coupling the double laser pulse to achieve the high CE and low debris. T. Higashiguchi et al., APL 88, 201503 (2006). T. Higashiguchi et al., APL 91, 151503 (2007). M. Kaku et al., APL 92, 181503 (2008).