laser produced plasma for euv radiation sources on asian
TRANSCRIPT
1st Asia Summer School on Laser Plasma Acceleration and Radiation, Beijing, Aug. 7-11, 06 1
In collaboration with K. Fujima, H. Furukawa, T. Kagawa, Y-G. Kang, T. Kato, F. Koike, R. More, M. Murakami, T. Nishikawa, A. Sasaki, A. Sunahara, H. Tanuma, V. Zhakhovskii, S. Fujioka, H. Nishimura, Y. Shimada, K. Nagai, N. Miyanaga, Y. Izawa and K. Mima
Laser Produced Plasma for EUV Radiation Sources
Katsunobu Nishihara (西原 功修)Institute of Laser Engineering, Osaka University
15 nm CMOS (AMD, 2001)
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Laser Plasma Acceleration and Radiations
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Outline
- IntroductionBackground on EUVL ( Extreme Ultra Violet Lithography ), Radiation from LPP ( Laser Produced Plasma ) and choice of emitting materialSource requirements and possible design windows
- Basic physics of Laser Produced Plasmas for EUV SourceRadiative processes of Li, Xe and Sn excited atomsFeatures of laser produced plasmas
- Critical Issues and Results to Date in EUV Source DevelopmentCritical issues ( laser conditions)Results to date ( optimization of conversion efficiency, experiment and theory)Further optimization ( double pulse, laser wavelength )Other problem and future development ( debris, target supply )
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Laser Plasma Acceleration and Radiations
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- Background on EUVL ( Extreme Ultra Violet Lithography )
- Radiation from LPP ( Laser Produced Plasma ) and choice of emitting material
- Source requirements and possible design windows
Introduction
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100
200
300
500
700
20
30
50
70
101970 200019901980 2010
1000
2000
3000
g linei line
KrFArF
F2
EUV 13.5 nm
Reduction projection
Year
Min
imum
pro
cess
siz
e, w
avel
engt
h of
ligh
t (nm
)
Contact illumination
Moore’s lowx 0.7/3 yr.
1:1 projectionlithography
weak super resolution
strong super resolutionNow available@ 90 nm nodeNow possible@ 60 nm nodeSource: ArF Excimer @193 nm.will work down to - 45 nm (immersion)
Moore’s low requires to implement the EUV lithography technology in manufacturing until 2011
15 nm CMOS
(AMD, 2001)
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LLNL HP
EUVL system consists of reflective mirror optics, because of no transparent lens for EUV.
EUV lithography system
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Cross section of multilayer mirror
Ref
lect
ivity
Wavelength (nm)13
Mo/Si67.5% @ 13.42 nmFWHM = 0.56 nm
Mo/Be70.2% @11.34 nmFWHM = 0.27 nm
1.0
0.8
0.6
0.4
0.2
0.0141211
*M. Wedowski et al.,
Reflected light wave interfearconstructively with each others.
Reflectivity of multilayer Mo/Si mirror has a sharp peak (70%) at 13.5 nm
wavelength vs. photon energy 13.0 nm : 95.4 eV13.5 nm : 91.8 eV
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Laser plasma radiation Laser plasma radiation from a typical 30from a typical 30--100 100 eVeV electron temperature plasmaelectron temperature plasma
Spectrum consists of:• lines
( bound-bound transitions ),
• recombination radiation ( bound –free transitions )
• bremsstrahlung( free-free transition )
• For an optically thin plasma: Plines:Precomb:Pbrem = 100:10:1
Focusing optics
Plasma
Tin target
MonochromaticEUV imager
Radiation spectrum from laser produced plasma
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Sn
0
0.2
0.4
0.6
0.8
1
1.2
9 10 11 12 13 14 15 16 17
LPP_normDPP_norm
rela
tive
inen
sity
wavelemgth (nm)
Xe
Li
Sn, Xe, Li emit strong 13.5 nm light,however their spectra are quite different.
Details of emission mechanismsfor each materialwill be discussed later.
wavelength (nm)
wavelength (nm)
O5+ 2p-3d @17.3 nm
O5+ 2p-3p @15.0 nm
O6+ 1s2p-1s7d @7.9 nm
O5+ 2p-4d @12.9 nm
O5+ 2p-4p @11.6 nm
0
1
2
3
4
5
6
7
8
6 8 1 0 1 2 1 4 1 6 1 8 2 0 2 2
SnSnO2 (59%)SnO2(23%)
inte
nsity
@13
.5nm
(a.
u.)
wavelength (nm)
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High-power and high-reputation EUV light source is required for EUV lithography.
LLNL HP
Laser
Mo/Simultilayer collector mirror
Plasmaintermediate focus point
EUV source requirements
Wavelength 13.5 nm (2% bandwidth) --> Sn, Xe, Li
Etendue 1 ~ 3.3 mm2SrFrequency 10 - 100 kHz
Power stability ± 0.3% (3s, average over 50 shots)Life time 100 Gshots (about half year)
EUV Power 115 – 180 W (@ intermediate focus point)> 300 W (@ plasma source)
Conversion efficiency from laser to EUV > 1 %
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0
0.01
0.02
0.03
0.04
1010 1011 1012
CEtCEh
conv
ersi
on e
ffeci
ency
laser intensity (W/cm2)
theory
from high density
laser intensity dependence of the conversion efficiency (Sn)
We have experimentally and theoretically shown thatthe source requirements for practical use can be achieved.
executivesummary
EUV power at intermediate focus point
PEUV = ηEUV S IL τEUV εtotal Rp= 280 W > 115 W
laser intensity : IL = 1011 W/cm2, pulse width : τEUV = 5 ns,repetition rate : Rp = 10 kHz , plasma size ( εt = 3 mm2str ) :
φ ≈870μmconversion efficiency :
ηEUV = 0.03efficiency of focusing system :
εtotal = εΩ εR εte εtd = 0.325/2π, 0.55, 0.9, 0.8
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- Radiative processes of Li, Xe and Sn excited atoms
- Features of laser produced plasmas density, temperature and radiation
Basic physics of Laser Produced Plasmas for EUV Source
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O5+ 2p-3d @17.3 nm
O5+ 2p-3p @15.0 nm
O6+ 1s2p-1s7d @7.9 nm
O5+ 2p-4d @12.9 nm
O5+ 2p-4p @11.6 nm
0
1
2
3
4
5
6
7
8
6 8 1 0 1 2 1 4 1 6 1 8 2 0 2 2
SnSnO2 (59%)SnO2(23%)
inte
nsity
@13
.5nm
(a.
u.)
wavelength (nm)
Sn
0
0.2
0.4
0.6
0.8
1
1.2
9 10 11 12 13 14 15 16 17
LPP_normDPP_norm
rela
tive
inen
sity
wavelemgth (nm)
Xe
Li
Sn, Xe, Li emits strong 13.5 nm light,Their spectral profiles are quite different.
Sn UTA (Unresolved Transition Array)
Xe(optical thick case)
Li thin line (single transition)
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Lithium Atomic Process
13.5 nm => Lyman- α (1s-2p)
1s-2p1s-3p
Te = 30 eV, Ni = 1019 cm-3
Stark Broadening
H-like Ground (1s)
Fully Ionized
He-like Ground (1s2)Lithium Ground (1s22s)
n = 3 (3p, 3s, 3d)n = 2 (2p, 2s)
n = 2 (1S0, 3S1, 1P1, 3P1,2,3)
-122 eV
-197 eV
0 eV
-202 eV
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principal total orbital angular momentumquantum number
l = 0, l = 1, l = 2, l = 3,n = 5 (5s)2 (5p)6
n = 4 (4s)2 (4p)6 (4d)10
n = 3 (3s)2 (3p)6 (3d)10
n = 2 (2s)2 (2p)6
n = 1 (1s)2
n = 5 (5s)2 (5p)2
n = 4 (4s)2 (4p)6 (4d)10
n = 3 (3s)2 (3p)6 (3d)10
n = 2 (2s)2 (2p)6
n = 1 (1s)2
Xe
Sn
2n2, n ≥ l + 1
Atomic structure of Xe (atomic number 54) and Sn (atomic number 50)
n = 4 (4s)2 (4p)6 (4d)8 (4d-5p) transition Xe+10
n = 4 (4s)2 (4p)n (4d)n’ (4d-4f) transition Sn+8 - +14
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11 nm13.5 nm
6 12 18 24In
tens
ity /
arb.
uni
ts
Wavelength / nm
q = 18
17
16
15
14
13
q = 8
12
11
10
9
Xeq+ - He
4d-5f
4d-5p
4d-5p
4d-4f
13.5nm
ECRIon Source
MCI
GrazingIncidence
SpectrometerCooled CCDGas
TMPTMP
charge exchange spectroscopy :Xe+q + ( He, Ar, Xe)
Xe+q-1 ( n, l ) Xe+q-1 ( n’, l’ ) + hν
EUV spectra from individual charge state ions
HULLAC
Emission at 13.5 nm comes from only Xe+10 ion stagecorresponding to 4d-5p resonance transitions
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CRECollisionalRadiativeEquilibrium
Abundance of Xe ions (temperature dependence)
Electron temperature (~30eV) should be chosen properly for Xe
Xe+10
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Spectral shape strongly modified by opacity and satellite lines
long pulse 15 ns
Optically thick Optically thinner
short pulse 170 ps
Optically thick plasma is required for increase 13.5 nm emissionfor Xe.
In optical thick plasma, emission around 11 nm is limited by Planck
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Planck distribution function 13 nm (95.4eV) 2% bandwidth
πIνp(dν/dλ)Δλ
1.66 x 109 W/cm2 (T=33.8eV)
Radiation flux is limited by Planck distribution function
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13.5 nm
5 10 15 20 25 30 35 40
Inte
nsity
/ ar
b. u
nits
Wavelength / nm
q = 15
14
13
6
12
11
10
9
Snq+ - Xe
8
5
q = 7
EUV spectra from individual charge state ions
Many ion species contribute to the UTA (Unresolved Transition Array)in Xe
charge exchange spectroscopy :Sn+q + ( He, Ar, Xe)
Sn+q-1 ( n, l ) Sn+q-1 ( n’, l’ ) + hν
4d-5p4d-4f
4d-5f
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only 4f-excitation
only 4p-excitation
4f and 4p-excitation
Spectral shift and narrowing occur for ions having 4d-open valence shell, due to configuration interaction.
The Sn UTA is due to 4p64dn ( 4p54dn+1 + 4dn-14f + 4dn-15p ) (n=0,1,,,9)transitions.
4f4d4p
4f4d4p
Overlapping of wave function causes resonant interaction among them
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Opacity effects are important in Sn : proper pulse duration is required (will be discussed later)
laser intensity1011 W/cm2
target; plane Sn foilwavelength; 1.064 μm (1 beam/normal incidence)pulse duration : 2.2 ns (Gaussian)spot size; 660 μmφ
8.0 ns (Gaussian)480 μmφ
Opacity measurement is important (will be discussed later)
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Example of radiation spectrum of a body with a temperaturewhich decreases toward the surface
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Corona region : high temperature / low density / CRE / M-, N- band emission
/ isothermal expansion
High density region: high density / low temperature / LTE / b-f absorption
Sn target
IL = 1011 W/cm2
τL = 2.2 ns
ni
Te
<Z>
vi
Features of laser produced high Z plasma, which consists of two regions.
laser
1017
1018
1019
1020
1021
1022
1023
0
10
20
30
40
50
60
-50 0 50 100 150
Sn 1w 1X1011W/cm2 2.2nsio
n de
nsity
(cm
-3)
Te (e
V),
<Z>
Position (μm)
0
2
4
6
8
10
fluid
vel
ocity
(X10
6 cm
/s)
tcx
isentxn
−
= 0),(
sctxtxv +=),(
Teconstant
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1017
1018
1019
1020
1021
1022
1023
0
10
20
30
40
50
60
-50 0 50 100 150
Sn 1w 1X1011W/cm2 2.2ns
ion
dens
ity (c
m-3
)
Te (e
V),
<Z>
Position (μm)
0
2
4
6
8
10
fluid
vel
ocity
(X10
6 cm
/s)ni Te
vi
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
EU
V fl
ux (X
109 W
/cm
2 )1017
1018
1019
1020
1021
1022
1023
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
-50 0 50 100 150
ion
dens
ity (c
m-3
)
Ener
gy fl
ux (X
1011
W/c
m2 )
Position (μm)
Laser
Radiation
Electron
EUVni
Most of absorbed energy flux is emitted by radiation, andEUV (13.5 nm) emission from corona.
various energy fluxesin laser ablation
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1017
1018
1019
1020
1021
1022
1023
1010
1011
1012
1013
1014
-50 0 50 100 150
ion
dens
ity (c
m-3
)
Ener
gy s
ourc
e (W
/cm
3 /13.
5nm
2%
BW
)
Position (μm)
1017
1018
1019
1020
1021
1022
1023
0
10
20
30
40
50
60
-50 0 50 100 150
Sn 1w 1X1011W/cm2 2.2ns
ion
dens
ity (c
m-3
)
Te (e
V),
<Z>
Position (μm)
0
2
4
6
8
10
6
ni Te
vi
EUV ( 2% bandwidth )emissivity,self absorption
ni
Self–absorption of EUV radiation can not be ignored for tin.
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From energy flux conservation in isothermal expansion region,various loss fluxes and electron temperature can be estimated.
corona plasma:isothermal expansion (density, velocity)
seessikin cTnTnZcnmcdxnmvdtdI 00
*0
2
0
2 ),(321
21
=+= ∫∞
1. expansion kinetic energy loss flux
seeeionion cnTTnZTnEI 00*
0 ),(23),( ⎥⎦
⎤⎢⎣⎡ +=
2. ionization and internal energy loss flux
νκ νν dxdxdTnTnjIx
eieirad ∫ ∫ ∫∞ ∞ ∞
⎟⎟⎠
⎞⎜⎜⎝
⎛′−=
0 0
),(exp),(
3. radiation energy flux
tcx
isentxn
−
= 0),( sctxtxv +=),(
1017
1018
1019
1020
1021
1022
1023
0
10
20
30
40
50
60
-50 0 50 100 150
Sn 1w 1X1011W/cm2 2.2ns
ion
dens
ity (c
m-3
)
Te (e
V),
<Z>
Position (μm)
0
2
4
6
8
10
fluid
vel
ocity
(X10
6 cm
/s)ni Te
vi
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Sn, 5ns
Dependence of various loss fluxes and electron temperature (difference of their dependence for Sn and Li)
Radiation loss dominates for Sn,Ionization and kinetic loss increase at low intensity.
109
1010
10
100
109 1010
loss
flux
es [W
/cm
2 ]
electron temperature [eV]
laser intensity [W/cm2]
radiation
Te
ionization
kinetic
Li, 20ns
Ionization loss dominates at low intensityand kinetic loss increases at high intensityfor Li.
109
1010
1011
10
100
1010 1011
loss
flux
es [W
/cm
2 ]
electron temperature [eV]
laser intensity [W/cm2]
radiationT
e
ionization
kinetic
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- Critical issuesatomic data, conversion efficiency, optimization
- Results to date (optimization of conversion efficiency)laser, experiments, simulation and modeling
- Further optimizationpulse duration, laser wavelength, double pulse etc.
- Other problems and future developmentfast ion, debris mitigation and target supply
Critical Issues and Results to Date in EUV Source Development
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Sn: Sn+8 - Sn+14 (4d-4f) Xe: Xe+10 (4d-5p) Li: Ly-α(many lines 105) (more than 100 lines) (narrow bandwidth)
transitions are not assigned for Sn and Xe yet
0
0.2
0.4
0.6
0.8
1
1.2
9 10 11 12 13 14 15 16 17
LPP_normDPP_norm
rela
tive
inen
sity
wavelemgth (nm)
O5+ 2p-3d @17.3 nm
O5+ 2p-3p @15.0 nm
O6+ 1s2p-1s7d @7.9 nm
O5+ 2p-4d @12.9 nm
O5+ 2p-4p @11.6 nm
0
1
2
3
4
5
6
7
8
6 8 10 12 14 16 18 20 22
SnSnO2 (59%)SnO2(23%)
inte
nsity
@13
.5nm
(a.
u.)
wavelength (nm)
Sn Xe Li
materials and transitions for 13.5 nm emission
understanding of atomic processes Importance of atomic data base
Research Issues: Understanding of Atomic Processes
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Research Issues: Optimization of LPP – EUV Source
laser pulse duration (ns)
Lase
r int
ensi
ty(W
/cm
2 )
100101
10 10
10 9
10 11
10 12 EUV conversion efficiency2%4%2%4%
Etendue = 1 mm2sr(source size = 700µm)
Etendue = 3.3 mm2sr(source size = 1300µm)
0.86 J1.7 J
laser energy
EUV source power = 350 W/2πsrrepetition rate = 10 kHz
laser energy, intensity and pulse durationin order to satisfy light source requirement
optimum laser intensityto obtain a maximum conversion efficiency from laser energy to EUV radiation energyof13.5 nm with 2% bandwidth
importance of EUV data base
understanding of dependence of the conversion efficiency on ・laser intensity and ・pulse duration
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Research Issues: Optimization of LPP – EUV Source80
0-12
00µm
Etendue≈ 1-3 mm2sr
θ
Optically thin limitI EUV(θ) = const
Optically thick limitI EUV(θ) = cos(θ)
d
optically too thin
optimum density-depth product1
2
510
2
510
2010.6 μm
τL=
plas
ma
scal
e le
ngth
(μm
)
10
100
1000
1017 1018 1019 1020
ion number density (cm-3)
etendue limit
1mm
2sr (Ω=π)
1.06 μm0.53 μm0.25 μm
12
510
1ns2ns
5ns10ns
20ns
optically too thick
one dimensional expansion
multi dimensional expansion
importance of EUV data base
understanding of dependence of the conversion efficiency on ・laser intensity (optimum ele. temp.),・pulse duration (plasma size) and・laser wavelength (ion density)
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agreement of theory and exp.spectra Xe, 13.5 nm
comparison of theory and exp.Xe energy levels
4 6 8 10 12 14 16 186
8
10
12
14
16
18
20
Wavelength /nm
Cha
rge
stat
e of
Xe
ions 捧 : Xe target
批 : He target
披 : HULLAC
4d-4f
4d-5p4d-5f 13.5nm
12.5 13 13.5 14 14.5
NIST data Xe10+
TMU CXS Xe11+ - He
Nor
mal
ized
Inte
nsity
Wavelength / nm
wavelength [nm]
EUVA
NIST
HULLAC
Cowan
Grasp12.5 13 13.5 14 14.5
Theoretical values near 13.5 nm agree with observation for Xe, but not for 4d-4f transitions with schematic differences of 0.4 nm for Xe & Sn.
comparison of theory and exp.Sn energy levels
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An ideally “uniform” EUV radiator was produced by GEKKO-XII laser, to obtain laser intensity dependence of the conversion efficiencywithout lateral energy loss and geometrical effects.
spherically uniform plasmasLaser :GEKKOXII, 12 beamswavelength: ω (1.056 mm)intensity: 1010 ~ 1012 W/cm2
pulse width: 1.2 ns (FWHM, Gaussian)
Target :Sn coated on a plastic ball300~2000 mmf ( mostly 700 μmφ)
Diagnostics (XST: time resolved):E-MON ( 13.5 nm 2% bandwidth )transmission grating (TDI) + CCDgrazing incident spectrometers (GIS)
GXII laser:12beam、20kJ/1ns
Target chamber
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G = 1.45f = 200 mm
4 mm Rod30 W
6 mm Rod80 W
FFP NFP
10 Hz / 10kHz Laser System, Target Chamber for EUV Lithography
2004.6.12 AM2:00
透過型回折格子
斜入射回折格子
EUVエネルギーモニター
EUV単色カメラ
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Diagnostics
t
x
x
λ
共同利用実験設備
monochromatic EUV mini-calorimeter
Grazing-incidence flat field spectrometer
45
Spherical mirror
Grating (1200 grooves/mm)
Back-illuminated CCD camera
祄Slit (500 )
θTarget
Laser 10 ns, 10 Hz ?3 J on target,
E-mon
Photo diode
Zr/CH filter
Mo/Si ML mirror
Schwarzschild microscope
Streak camera
Mo/Si ML mirrors filter: Zr/CH
祄 (0.4/0.5 ) Optical probe
Gated CCD camera
Interferometer
Δx 祄 = 15 Δt = 2.6 ns
Δt = 1 ns
Δλ= 0.057 nm @ 17.3 nm Δx 祄 = 50
neutral particle (LIF)
ion (Thomson parabola)
electron density(interferometer)
1st Asian Summer S
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Laser Plasma Acceleration and Radiations
1st Asia Summer School on Laser Plasma Acceleration and Radiation, Beijing, Aug. 7-11, 06 36
target; Sn coated spherical CHlaser; Gekko-XII/Nd glass laser/12 beamswavelength; 1.053 μmpulse duration : 1.2 ns (Gaussian)
Conversion efficiency of uniformly irradiated spherical target
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
Con
vers
ion
Effic
ienc
y(%
)
10102 3 4 5 6 7
10112 3 4 5 6 7
1012
Intensity (W/cm2)
Y. Shimada et al.,Appl. Phys. Lett., 86, 051501 (2005).
E-monTGS
1st Asian Summer S
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Laser Plasma Acceleration and Radiations
1st Asia Summer School on Laser Plasma Acceleration and Radiation, Beijing, Aug. 7-11, 06 37
Comparison of experimental and theoretical EUV spectra for spherical target
IL= 9E+10 W/cm2 IL=3E+11 W/cm2 IL=9E+11 W/cm2
experiments
simulations
0
500
1000
1500
2000
0 5 10 15 20
Inte
nsity
(a.u
.)
Wavelength (nm)
0
500
1000
1500
2000
0 5 10 15 20
y(
)
Wavelength (nm)
0
500
1000
1500
2000
0 5 10 15 20In
tens
ity (a
.u.)
Wavelength (nm)
1st Asian Summer S
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Laser Plasma Acceleration and Radiations
1st Asia Summer School on Laser Plasma Acceleration and Radiation, Beijing, Aug. 7-11, 06 38
Dog-bone gold cavity
Opacity sample(Sn with CH tamper)
Sn plate for probingx-ray source
Thermal radiation(TR = 50 eV)
Schematic of opacity measurement
10 12 14 16 18
1
2
3
4
5
Wavelength (nm)
Time (ns)
10 12 14 16 18
1
2
3
4
5
Wavelength (nm)
Time (ns)
10 12 14 16 18
1
2
3
4
5
Wavelength (nm)
Time (ns)
10 12 14 16 18
1
2
3
4
5
Wavelength (nm)
Time (ns)
① Opacity (Sn) ② Self-emission (Sn)
③ Opacity (CH) ④ Self-emission (CH)
Sn Opacity
Tim
e
Wavelength
13.5 nm
Opacity of Sn heated by thermal radiation (TR = 50 eV) has been measured
2
3
4
5
6
7
8
9100
Rad
iatio
n te
mpe
ratu
re (e
V)
3 4 5 6 7 8 9100
2 3 4 5 6 7 8 91000
Laser energy (J)
TR = (EL/σ)1/4
Laser inlet hole
Observation window
1st Asian Summer S
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Laser Plasma Acceleration and Radiations
1st Asia Summer School on Laser Plasma Acceleration and Radiation, Beijing, Aug. 7-11, 06 39
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Tran
smis
sion
18161412108Wavelength (nm)
Experiment (raw) Experiment (smooth)
Absorption spectrum of 30-eV tin
HULLAC
Theoretical opacity obtained from HULLAC code roughly agrees with the experiments, but not in detail.
1st Asian Summer S
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Laser Plasma Acceleration and Radiations
1st Asia Summer School on Laser Plasma Acceleration and Radiation, Beijing, Aug. 7-11, 06 40
Conversion efficiency from laser to EUV emission is obtainedfrom various loss fluxes determined from power balance.
kinionrad
HDEUVCREUVEUV III
II++
+= ,,η
conversion efficiency
2,
,EUVrad
CREUV
II =
22)( 4
,,rad
RREUVPHDEUVITTII == σ
laser intensity dependences of various loss flux and electron temperature
radiation loss dominates(Sn, n0 = 4x1019 cm-3, 1.2ns)
109
1010
1011
10
100
1010 1011
loss
flux
es [W
/cm
2 ]
electron temperature [eV]
laser intensity [W/cm2]
radiationT
e
ionization
kinetic
1st Asian Summer S
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On
Laser Plasma Acceleration and Radiations
1st Asia Summer School on Laser Plasma Acceleration and Radiation, Beijing, Aug. 7-11, 06 41
0
0.01
0.02
0.03
0.04
1010 1011 1012
CEtCEh
conv
ersi
on e
ffeci
ency
laser intensity (W/cm2)
theory
from high density
EUV power at intermediate focus point
PEUV = ηEUV S IL τEUV εtotal Rp= 280 W > 115 W
laser intensity : IL = 1011 W/cm2, pulse width : τEUV = 5 ns,repetition rate : Rp = 10 kHz , plasma size ( εt = 3 mm2str ) :
φ ≈870μmconversion efficiency :
ηEUV = 0.03efficiency of focusing system :
εtotal = εΩ εR εte εtd = 0.325/2π, 0.55, 0.9, 0.8
Theoretical conversion efficiency obtained from the power balance model agrees fairly well with the experiments with tin, in which CE 3% is achieved at 5x1010 - 1011 W/cm2.
laser intensity dependence of the conversion efficiency
1st Asian Summer S
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Laser Plasma Acceleration and Radiations
1st Asia Summer School on Laser Plasma Acceleration and Radiation, Beijing, Aug. 7-11, 06 42
電子密度干渉計測
@2ω
@4ω
EUV発光ピーク
@2ω
@4ω
@2ω
@4ω
EUV発光ピークEUV発光ピーク
0.53-µm (2ω) probe
0 200 400Distance (µm)
Target surface0.53-µm (2ω) probe
0 200 400Distance (µm)
Target surface
2d radiation-hydrosimulation
electron density measurementwith interference of 2 ω or 4 ω
Electron density obtained from 2d radiation hydrodynamic simulationagrees well with experiments, which indicates spherical expansion.
1D Sim.2D Sim. with 1D cond.2D Sim.
1st Asian Summer S
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Laser Plasma Acceleration and Radiations
1st Asia Summer School on Laser Plasma Acceleration and Radiation, Beijing, Aug. 7-11, 06 43
- Critical issuesatomic data, conversion efficiency, optimization
- Results to date laser, experiments, simulation and theoretical model
- Further optimizationpulse duration, laser wavelength, double pulse etc.(theoretical and experimental works)
- Other problems and future developmentfast ion, debris mitigation and target supply
Critical Issues and Results to Date in EUV Source Development
1st Asian Summer S
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Laser Plasma Acceleration and Radiations
1st Asia Summer School on Laser Plasma Acceleration and Radiation, Beijing, Aug. 7-11, 06 44
Further optimization for 1μm laser (Sn : planer target)
1017 1018 1019 1020
ion density [cm-3]
10
20
30
50
80
elec
tron
tem
pera
ture
[eV]
1017 1018 1019 1020
ion density [cm-3]
10
20
30
50
80
elec
tron
tem
pera
ture
[eV]
pulse width (solid line:ns)max. CE (solid line; %)
For 1μm laser,max CE = 3 % at 1010-1011 W/cm2, and 2 ns
Dependence of max. conversion efficiency,optimum pulse duration and required laser intensity (dotted line) on electron temperature and ion density
1st Asian Summer S
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Laser Plasma Acceleration and Radiations
1st Asia Summer School on Laser Plasma Acceleration and Radiation, Beijing, Aug. 7-11, 06 45
High conversion efficiency was obtained at 2.3 ns pulse duration, which agrees with theoretical prediction.
2.0
1.5
1.0
0.5
Con
vers
ion
effic
ienc
y (%
)
10102 3 4 5 6 7 8
10112 3 4 5 6 7 8
1012
Laser intensity (W/cm2)
1.2 ns pulse duration 2.3 ns pulse duration 5.6 ns pulse duration 8.5 ns pulse duration
Dependence of CE on pulse duration and laser intensity
1st Asian Summer S
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Laser Plasma Acceleration and Radiations
1st Asia Summer School on Laser Plasma Acceleration and Radiation, Beijing, Aug. 7-11, 06 46
dotted line:13.5nm absorption length (cm)Solid line:10.6μm laser absorption length (cm)
dependence of absorption lengths of laser and EUV破線:13.5nm EUV (cm)実線:1.06μm laser (cm)
Optimization for different laser wavelength : absorption lengths of both laser and EUV lights should be comparable.
optimum density optimum density
1.06 μm10.6 μm
1st Asian Summer S
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Laser Plasma Acceleration and Radiations
1st Asia Summer School on Laser Plasma Acceleration and Radiation, Beijing, Aug. 7-11, 06 47
1017 1018 1019 1020
ion density [cm-3]
10
20
30
50
80
elec
tron
tem
pera
ture
[eV]
1017 1018 1019 1020
ion density [cm-3]
10
20
30
50
80
elec
tron
tem
pera
ture
[eV]
optimum pulse width (ns)Max. CE (white solid line:%)
Optimum parameters for different laser wavelengths
Low density region (10.6μm laser): low intensity,long pulse
High density region (1.06μm laser): high intensity,short pulse
1st Asian Summer S
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Laser Plasma Acceleration and Radiations
1st Asia Summer School on Laser Plasma Acceleration and Radiation, Beijing, Aug. 7-11, 06 48
T. Higashiguchi et al., APL 88, 201503 (2006)T. Higashiguchi et al., SPIE 6151, 615145 (2006).
Experimental conditions,Main pulse: 1.064 μm/ 10 ns/ 1011-1012 W/cm2,spot size : 175 μmφ, 3x1011 W/cm2
Pre-pulse: 532 nm/ 8 ns/ 2x1010 W/cm2
Target: liquid micro-jet with SnO2 (6-17%)
6%
Increase of conversion efficiency with double pulses (Miyazaki)
1st Asian Summer S
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Laser Plasma Acceleration and Radiations
1st Asia Summer School on Laser Plasma Acceleration and Radiation, Beijing, Aug. 7-11, 06 49
Research Issues: Mitigation of Fast Ions and Debris
intermediate focus point
to irradiation optical system
laser
collecting mirrorEUVsource
damage of collector mirror by fast ion and neutral atoms
development of・ high replete target supply・ minimum mass target
understanding of・ dependence of fast ion spectrum
on laser parameters andtarget initial density etc.
・ charge exchange andrecombination processes
・ mitigation by such asmagnetic field
MD with electron dynamics
1st Asian Summer S
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Laser Plasma Acceleration and Radiations
1st Asia Summer School on Laser Plasma Acceleration and Radiation, Beijing, Aug. 7-11, 06 50
10-6
10-5
10-4
10-3
10-2
10-1
100
0.1 1 10
Ion kinetic energy ε (keV)
Experiment
(α =1, ε0=1.7 keV)
Nor
mal
ized
spe
ctru
m d
N/d
ε
Present model
1Maximum ion energy predicted by the present analytical model
Sn固体平板ターゲット
レーザー
Quasi-Planar Expansion100 μm
500 μm
10-4
10-3
10-2
10-1
100
0.1 1 10
Nor
mal
ized
spe
ctru
m d
N/dε
Ion kinetic energy ε (keV)
Experiment
Present model
1
(α =3, ε0= 3.0 keV)
Maximum ion energy predicted by the present analytical model
Xe液体ジェット
レーザー
Quasi-Spherical Expansion10 - 20 μm
Isothermal expansion with finite target mass causes fast ions.
Details can be presentedon Thursday by Murakami
1st Asian Summer S
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Laser Plasma Acceleration and Radiations
1st Asia Summer School on Laser Plasma Acceleration and Radiation, Beijing, Aug. 7-11, 06 51
1.5
1.0
0.5
0.0
Con
vers
ion
effic
ienc
y (%
)
5 6 7 810
2 3 4 5 6 7 8100
2 3 4 5 6 7 81000
Sn layer thickness (nm)
800
600
400
200
0
Emission intensity from
Sn(I) atoms
EUV-CEs
Emission of Sn0+
PoP 05, 06
CE of EUV & emission from neutral atoms vs thickness of Sn
Minimum mass target is required to reduce neutral atoms
1st Asian Summer S
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Laser Plasma Acceleration and Radiations
1st Asia Summer School on Laser Plasma Acceleration and Radiation, Beijing, Aug. 7-11, 06 52
Minimum mass target can be realized with use of a droplet targetand punch-out targetDroplet target
prepulse
main laser
Concept of the punch-out target
100 m/s100 m/s100 m/s
Punch-out target
1st Asian Summer S
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Laser Plasma Acceleration and Radiations
1st Asia Summer School on Laser Plasma Acceleration and Radiation, Beijing, Aug. 7-11, 06 53
⎟⎟⎠
⎞⎜⎜⎝
⎛⎟⎟⎠
⎞⎜⎜⎝
⎛ ΛΛ≈=
2ln
2ln2
21 22
2maxmax ei TzvmE
eeDe Tn
TnzReR 31
0
0
020
2
2
202 ∝==Λ
ελconstnRN == 0
303
4π
Maximum ion energy
Fast ion energy can be reduced for low initial target density
Punch-out target,double pulse can reduce initial density and fast ion energy
Single pulse Dual pulses
(Δτ = 100 ns)10 3
10 4
10 5
10 6
Ion
num
ber
3 4 5 6 7 8 910 3
2 3 4 5 6 7 8 910 4
Ion energy (eV)
Punch -out
Static
Sn 1+ Sn 2+
Sn 1+
Sn 2+
Sn 3+
10 3
10 4
10 5
10 6
Ion
num
ber
3 4 5 6 7 8 910 3
2 3 4 5 6 7 8 910 4
Ion energy (eV)
Punch -out
Static
Sn 1+ Sn 2+
Sn 1+
Sn 2+
Sn 3+
1st Asian Summer S
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Laser Plasma Acceleration and Radiations
1st Asia Summer School on Laser Plasma Acceleration and Radiation, Beijing, Aug. 7-11, 06 54
Mitigation of fast ions by magnetic field
Gyro-radius of fast ions
( )ZeBEmvR i
ciL
21maxmax 2
==ω
B = 1 T Emax = 10 keVZ = 1
RL = 11 cm
0.0001
0.001
0.01
0.1
1
0 0.2 0.4 0.6 0.8 1 1.2center magnetic field [T]
Ion
sign
al [a
.u.]
Reduction of damage by B-field
Stability of expanding plasma depends on B-field configuration
1st Asian Summer S
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Laser Plasma Acceleration and Radiations
1st Asia Summer School on Laser Plasma Acceleration and Radiation, Beijing, Aug. 7-11, 06 55
Summary
I have shown that laser-produced-plasma EUV source can be achieved for practical use of next generation lithography although technical problems, such as debris mitigation, still remain.
Understanding of fundamental physics is always importantfor any practical applications.
1st Asian Summer S
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Laser Plasma Acceleration and Radiations
1st Asia Summer School on Laser Plasma Acceleration and Radiation, Beijing, Aug. 7-11, 06 56
Acknowledgements
Thanks for providing power point files for the lecture, especially
S. Fujioka, M. Murakami, (ILE)T. Higashiguchi (Miyazaki)T. Nishikawa (Okayama)G. O’Sullivan (Dublin)A. Sunahara, (ILT)A. Sasaki, (JAEA)H. Tanuma (TMU)
謝謝 Thank you for your attention
1st Asian Summer S
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Laser Plasma Acceleration and Radiations