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Contents・Comparison of Theory with Experiments
LPP EUVLA-DPP EUV
・Plasma Conditions for High CELPP EUV Light SourceLA-DPP Light Source
Optimum Plasma Conditions for LPP- and LA-DPP- EUV Sources
Katsunobu Nishihara1, Atsushi Sunahara2, Akira Sasaki3, Hiroshi Komori4, Akira Sumitani4, Kiichiro Uchino5, Yusuke Teramoto6, Kazuaki Hotta6, Eiki Hotta7
1 Institute of Laser Engineering, Osaka University, 2 Institute for Laser Technology, 3 Quantum Beam Science Directorate, Japan Atomic Energy Agency, 4 EUVA(Hiratsuka),
5 University of Kyushu, 6 EUVA(Gotenba), 7 Tokyo Institute of Technology
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0 1 1010 2 1010 3 1010 4 1010 5 1010
SESAME
4mm7mm9mm
Trav
elin
g tim
e (n
s)
Laser intensity (W/cm2)
Hotta at Tokyo IT
Plasma Expansion (Sn+1 (529nm)) (EL:129mJ)
simulated time evolution of visible light emission from plasma
dependence of plasma arrival time on laser intensity and electrode voltage
LA-DPP 1 Expansion dynamics of laser produced plasma agrees fairly well with experiments observed at Tokyo Inst. Tech (Hotta et al).
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Sphere A
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ion
dens
ity (c
m-3
)
Position (μm)
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Sphere A
-20ns-10ns0ns10ns20ns30ns40ns50ns60ns70ns80ns90ns100ns110ns120ns130ns140ns150ns
T e (eV)
Position (μm)
LA-DPP 2
electron temperaure (EUVA)
electron density (EUVA)
electron temperature profile
ion density profile
Expansion dynamics of laser produced plasma agrees fairly well with experiments observed at EUVA (PHILIPS).
Effects of Applied Voltage on Laser-Produced-Plasma Expansion
Applied voltage affects plasma expansion only near the anode(1.5 times expansion velocity in experiment)But, electrons accelerated cause sputteringon the anode and generated plasma there
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106107108109
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g0-v0
F elect with E=20kV.Pressure with F elect E=20kVPressure w/o F
Pres
sure
(dyn
/cm
2)Time (nsec)
electric force
Plasma pressure
Comparison of plasma pressure and electric force
Hotta at Tokyo ITA A
Model
LA-DPP 3
LA-DPP (cathode) strong emission appears at anode andPlasma pinch near cathode (Tokyo Inst. Tech.)
θ
Ωd
Incident Laser BeamPlasma
Scattered light
0: λWavelength
・10 pm required resolution
100 pm
ion wave
electron wave 10 nm
electron density electron density nnee
electron temperature electron temperature TTee,,
charge state charge state ZZ
Electron density and temperature of LPP agrees wellwith experiments observed at Kyushu Univ. (Uchino et al))
ne = 2.0×1018 cm-3
Te = 12±1 eVZ = 4
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t=+15nsrinit
=500μm
Num
ber d
ensi
ty (c
m-3
)
Tem
pera
ture
(eV)
Radius (μm)
PoP experiment using carbon target
LPP 1
Thomson scattering measurement
LPP 2 High CE can be obtained even for relatively long laser pulse > 40 nsdue to 3-dimensional expansion of CO2 laser
elec
tron
tem
pera
ture
(eV
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0time (ns)euspec
-50 0 50 100time (ns)
conv
ersi
on e
ffici
ency
(%)
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rising time:25ns falling time:75ns (FWHM) Gaussian pulse (laser intensity: 4x1010 W/cm2, modulation: 0.5, period of moduration: 10ns)
laser spot size of 1mm Corresponding to UCSD experiment
LPP 3 Simulated EUV spectra show no differencebetween w/wo modulation (no opacity effects even for long pulse)
without modulation modulated (0.5, 10ns)
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spectrumT2-4-0-100ns-200um
2R/Unm
hv(nm) wavelength (nm)10 15 205
EUV
spec
trum
(au)
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spectrumT2-4-05-10-100ns-200um
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hv(nm) EU
V sp
ectr
um (a
u)0
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wavelength (nm)10 15 205
rising time:25ns falling time:75ns (FWHM) Gaussian pulse (laser intensity: 4x1010 W/cm2, modulation: 0.5, period of moduration: 10ns)
Theoretical Modeling of Plasma Parameters for High Efficiency EUV Light Sources
Optimum plasma conditions from power balance model(taking detail atomic processes into account)
・LPP EUV Light Source: absorbed laser intensity
radiation and expansion losses, energy flux required (planar target,non-stationery expansion)
evaluate Conversion Efficiency
・DPP EUV Light Source:plasma pressure magnetic pressure,radiation loss Joule heating
(cylindrical plasma,without taking pinching dynamics)evaluate Spectral Efficiency
LPP 1 Consideration of Minimum mass target for LPP1.7 ng -- 8 μm (diameter) for 5 mJ EUV per pulse
Sn minimum massfor 5mJ EUV output energy per shot
expansion of droplet target by pre-pulse(MD simulation)
symmetry number density
10 photons / ns / atom
emission time 4.4 nsduring expansion
conversion efficiency
pulse duration (ns)
100 ns 10 ns 1 ns
1.5 times longer
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elec
tron
tem
pera
ture
(eV)
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ion density (cm-3)
LPP 2 Sn density and temperature for the conversion efficiency of 5 – 6 %(optimum plasma parameter for CO2 laser)
8 % 6 % 4 %
laser spot size 500 μm,
repetition rate 100 kHz
100 ns31.6 ns10 ns3.16 ns1 ns
ion number density 5x1017 – 1018 cm-3, electron temperature 30 – 50 eV
EUV energy (mJ) / pulse
laser energy (mJ) / pulse
5 mJ
10 mJ 1000 W
500 W
200 mJ
150 mJ
20 kW
15 kW
laser spot size 600 μm,
repetition rate 100 kHz
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10
elec
tron
tem
pera
ture
(eV)
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ion density (cm-3)
EUV energy (mJ) / pulse EUV power
laser energy (mJ) / pulse laser power (kW)
LPP 3 EUV power of 500 – 1000 W can be obtained at optimum conditions(required CO2 laser power < 15 kW )
ion number density 5x1017 – 1018 cm-3, electron temperature 30 – 50 eV
AC
-+-
polarization scattering (dipole):
+- -
cross section of polarization scattering:inversely proportional to velocity
collision frequency: independent of velocity
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n de
nsity
(cm
-3)
Position (μm)
expansion of laser plasma
LA-DPP 1
local electric conductivity:determined from the ratio of local electron and gas density g
e
m
eDc n
nm
ne∝=
νσ
2
If the ratio is constant in space,both current density and electric field areuniform in space.
Electrons can be initially heated at low density region.(avalanche may start at low density region)
Ions accelerated to the cathode leads to sputtering and supply plasmaand plasma pinching occurs near the cathode
2
⎟⎟⎠
⎞⎜⎜⎝
⎛>∝Ε<
ge n
EmM
Uniform electric field and current can be obtained in dischargeeven in exponential density profile of LA expanding plasma
gd n
Ev ∝
0
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spectral efficiency
spec_eff(%)17spec_eff(%)18spec_eff(%)19
temperature T (eV)
DPP 2 High spectral efficiency > 25 % can be obtainedat relatively low density.
ni:1019cm-3
ni:1018cm-3 ni:1017cm-3
0.0
0.00020
0.00040
0.00060
0.00080
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0.0012
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0.0016
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50
2J/Unm
2J/Unm
hv(nm)
10 12 14 16 18 20wavelength (nm)
EU
V s
pect
rum
Te: 40 eVni: 3.7x1018 cm-3
Diameter: 100 μmφ
EUV spectrumobtained by simulation
Balance model shows that ion density > 1018 cm-3 , plasma radius < 100 μm, and electron temperature > 30 eV can be achieved.
DPP 3 EUV out put energy > 100 mJ / pulse can be obtainedwith electron temperature of 30 – 50 eV.
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radius_EUVpower090528
EUV(W/cm)17EUV(W/cm)18EUV(W/cm)19
temperature T (eV)
ni:1019cm-3
ni:1018cm-3
ni:1017cm-3
Under the assumptions of
pinch length: 1mmconfinement time: 20 ns
> 100 mJ / pulse
Summary
Plasma conditions for high CE are almost the same for LPP and LA-DPP,although their dynamics are quite different from each other,
ion number density: about 1018 cm-3, electron temperature: 40 – 50 eV.
CE of 4 – 6 % in LPPspectral efficiency > 25 % in LA-DPP.
Those can be achieved by double laser pulse scheme with CO2 main laser in LPP,laser produced and pinch plasma in LA-DPP.
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