Laser Produced Plasma for EUV Radiation Sources
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Katsunobu Nishihara (西原 功修）
Institute of Laser Engineering, Osaka University
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In collaboration with
P
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K. Fujima, H.
Furukawa, T. Kagawa, Y-G. Kang, T. Kato, F. Koike, R. More,
e
s T. Nishikawa, A. Sasaki, A. Sunahara, H. Tanuma, V. Zhakhovskii,
M. Murakami,
a
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S. Fujioka, H. Nishimura, Y. Shimada, K. Nagai, N. Miyanaga, Y. Izawa and K. Mima
15 nm CMOS
(AMD, 2001)
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
1
Outline
l
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Background on EUVL ( Extreme Ultra Violet Lithography
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Radiation from LPP ( Laser Produced Plasma
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r windows
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Source requirements and possible design
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m Plasmas for EUV Source
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- Basic physics of Laser Produced
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Radiative processesnof Li, Xe and Sn excited atoms d
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iaproduced plasmas
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Featurest of laser
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- Critical Issues and Results to Date in
EUV Source Development
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Critical issues ( laser conditions)le
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Results to date ( optimization
of conversion efficiency, experiment and theory)
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Further optimization ( A
double pulse, laser wavelength )
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Other problem and
mfuture development ( debris, target supply )
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- Introduction
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
2
Introduction
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- Background on EUVL ( Extreme Ultra Violet Lithography )
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- Radiation from LPP ( Laser
Produced Plasma ) and iat
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choice of emitting material
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- Source requirements
and
possible design
windows
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1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
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Moore’s low requires to implement the EUV lithography technology
in manufacturing until 2011
Contact illumination
Minimum process size, wavelength of light (nm)
3000
2000
1000
700
500
300
200
100
70
50
30
20
s
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10
1:1 projection
lithography
Moore’s low
x 0.7/3 yr.
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we n
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ak
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sup
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ng
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sup solu
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ti
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t
1
res on
a
olu
r
Now available@ 90 nm node
tie
on
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Now possible@ 60 nm node
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Source: ArF Excimer @193 nm.
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will work down to - 45 nm (immersion)
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Reduction projection
g line
i line
KrF
ArF
F2
EUV 13.5 nm
1970
1980
1990
Year
2000
2010
15 nm CMOS
(AMD, 2001)
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
4
EUVL system consists of reflective mirror optics,
because of no transparent lens for EUV.
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PEUV lithography system
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LLNL HP
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
5
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Reflectivity of multilayer Mo/Si mirror has a sharp peak (70%)
at 13.5 nm
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Reflected
olight wave interfear
h
constructively
with each others. s
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m(nm)
Wavelength
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*M. Wedowski et al.,
P
wavelength
vs.
photon
energy
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13.0
s nm : 95.4 eV
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L 13.5 nm : 91.8 eV
Cross section of multilayer mirror
Reflectivity
1.0
0.8
0.6
0.4
0.2
0.0
Mo/Be
70.2% @11.34 nm
FWHM = 0.27 nm
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12
Mo/Si
67.5% @ 13.42 nm
FWHM = 0.56 nm
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1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
6
Laser plasma radiation
from a typical 30-100 eV electron temperature plasma
Radiation spectrum from laser produced plasma
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Plasma
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Focusing optics
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recombination
t
1 radiation
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( bound –free transitions ) le
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bremsstrahlung
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( free-free transition
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For aneoptically thin plasma:
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LP :P :P = 100:10:1
Spectrum consists of:
• lines
( bound-bound transitions ),
•
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Monochromatic
EUV imager
Tin target
lines
recomb
brem
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
7
Sn, Xe, Li emit strong 13.5 nm light,
however their spectra are quite different.
1.2
Sn
S nO2 (59%)
S nO2(23%)
7
6
O 5+ 2p-4d
@12.9 nm
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4
3
2
1
0
O 5+ 2p-4p
@11.6 nm
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O 5+ 2p-3d
@17.3 nm
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1
ol
LPP_norm
DPP_norm
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wavelength (nm)
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Details of emission mechanisms
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for each material
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will be discussed later.
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0.4
6+
O 1s2p-1s7d
@7.9 nm
0.2
0
6
Li
O 5+ 2p-3p
@15.0 nm
Xe
relative inensity
Sn
intensity @ 13.5nm (a.u.)
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10 12 14 16 18 20 22
w a ve length ( nm)
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11
12
13
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wavelemgth (nm)
wavelength (nm)
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
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High-power and high-reputation EUV light source
is required for EUV lithography.
EUV source requirements
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Wavelength
13.5 nm (2% bandwidth) --> Sn, Xe, Li
EUV Power
115 – 180 W (@ intermediate focus point)
> 300 W (@ plasma source)
1 ~ 3.3 mm2Sr
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Frequency
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10 - 100 kHz
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Conversion
efficiency from
laser to EUV a
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>1%
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Power stability ± 0.3% (3s,
average
over 50 shots)
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Life time
100
Gshots
(about half year)
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Mo/Si
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multilayer collector
mirror
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Laser
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Plasma
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intermediate focus point
Etendue
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
9
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LLNL HP
We have experimentally and theoretically shown that
the source requirements for practical use can be achieved.
executive
summary
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laser intensity dependence of
EUVopower
hintermediate focus point s
the conversion efficiency (Sn)
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at
S
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=η
S I τ tεi R
P
0.04
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=
280
W
>
115
W
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0.03
n
laser
intensity
: I = 10 W/cm ,
theory
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pulse
width : τ
= 5 ns,
st As
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repetition rate : R = 10 kHz ,
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0.02
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r plasma size ( ε = 3 mm str ) :
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φ ≈870μm
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conversion efficiency :
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0.01
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η
= 0.03
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from
high
density
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efficiency of focusing system :
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P
0
ε
= ε ε ε ε = 0.32
r
10
10
10 e
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5/2π, 0.55, 0.9, 0.8
a
laser
intensity
(W/cm2)
L
EUV
conversion effeciency
CEt
CEh
EUV
L
EUV total
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L
EUV
p
２
t
EUV
10
11
12
total
Ω
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te
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
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td
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Basic physics of Laser Produced Plasmas for EUV Source
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- Radiative processes of Li, Xe and Sn excited atoms
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- Features of laser produced
plasmas
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mand radiation
density, temperature
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1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
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Sn, Xe, Li emits strong 13.5 nm light,
Their spectral profiles are quite different.
1.2
Sn
S nO2 (59%)
S nO2(23%)
7
6
5+
O 2p-4d
@12.9 nm
5
4
5+
O 2p-4p
@11.6 nm
5+
O 2p-3p
@15.0 nm
5+
O 2p-3d
@17.3 nm
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1
0.8
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0.6
0.4
6+
O 1s2p-1s7d
@7.9 nm
2
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0.2
1
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LPP_norm
DPP_norm
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Sn UTA
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(Unresolved Transition Array)
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Xe
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(optical thick case)
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Li thin line
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Li
Xe
relative inensity
Sn
intensity @ 13.5nm (a.u.)
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10 12 14 16 18 20 22
w a ve le ngth ( nm)
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13
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wavelemgth (nm)
(single transition)
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
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Lithium Atomic Process
13.5 nm => Lyman- α (1s-2p)
0 eV
-122 eV
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1
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1s-2p
1s-3p
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H-like Ground (1s) ler
ce,
n = 2 ( S , S ,cP
P ) a A
m
s
Te = 30 eV, Ni = 10
a
l
Stark Broadening
P
r
e He-like Ground (1s )
1
-197 eV
-202 eV
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Fully Ionized
n = 3 (3p, 3s, 3d)
n = 2 (2p, 2s)
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S
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1
1,2,3
Lithium Ground
2
(1s22s)
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
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cm-3
Atomic structure of
Xe (atomic number 54) and Sn (atomic number 50)
principal
quantum
number
Xe
Sn
n=5
n=4
n=3
n=2
n s=t 1
total orbital angular momentum
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l = 0, l = 1, l = 2, l = 3,
(5s)2 (5p)6
8
(4s)2 (4p)6 (4d)10
(4d-5p) transition Xe+10
(3s)2 (3p)6 (3d)10
(2s)2 (2p)6
(1s)2
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n=5
(5s) (5p) el
cc (4d)
(4d-4f) transition Sn
n=4
(4s) A
(4p)
a
n=3
(3s)
(3p) (3d)
m
n = 2 as (2s) (2p)
l (1s)
n =P1
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2
2
2
6n
n’
10
2
6
10
2
6
+8 - +14
2
La
s
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2n2, n ≥ l + 1
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
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Emission at 13.5 nm comes from only Xe+10 ion stage
corresponding to 4d-5p resonance transitions
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EUV spectra from
individual charge state ions
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4d-5p
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HULLAC io
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A
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13.5 nm
11 nm
m
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charge exchange
spectroscopy :
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P
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s
La
iat
4d-4f
Intensity / arb. units
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q = 18
17
16
15
14
13
4d-5p
12
13.5nm
4d-5f
ECR
Ion Source
11
10
9
q=8
Xe+q
Æ
+ ( He, Ar, Xe)
Grazing
Incidence
Spectrometer
Gas
Xe+q-1
( n, l )
Æ Xe+q-1 ( n’, l’ ) + hν
Cooled
CCD
Xeq+ - He
6
MCI
TMP
TMP
12
18
Wavelength / nm
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
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Electron temperature (~30eV) should be chosen properly for Xe
Abundance of Xe ions (temperature dependence)
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CRE
Collisional
Radiative
Equilibrium
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Xe
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+10
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1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
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Optically thick plasma is required for increase 13.5 nm emission
for Xe.
In optical thick plasma, emission around 11 nm is limited by Planck
Optically thick
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o Optically thinner
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s
O
t
s A
n 170 ps
o
long pulse 15 ns
shortipulse
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c
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Spectral shape strongly modified by
A
opacity and satellite lines
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1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
17
Radiation flux is limited by Planck distribution function
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πI (dν/dλ)Δλ
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s
S
n
r 1.66 x 10 W/cm (T=33.8eV)
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A
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Planck distribution function
13 nm (95.4eV) 2% bandwidth
νp
9
s
a
L
2
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
18
Many ion species contribute to the UTA (Unresolved Transition Array)
in Xe
EUV spectra from
individual charge state ions
1
A
A
a
m
s
la exchange spectroscopy :
13.5 nm Pcharge
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s
a
L
4d-4f
Æ Sn+q-1 ( n’, l’ ) + hν
t
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nd
Ra
s
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io
13
12
Snq+ - Xe
11
4d-5p
10
9
4d-5f
8
q=7
6
Sn+q + ( He, Ar, Xe)
Æ Sn+q-1 ( n, l )
q = 15
14
a
On
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Intensity / arb. units
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5
5
10
15
20
25
30
Wavelength / nm
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
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Spectral shift and narrowing occur for ions
having 4d-open valence shell, due to configuration interaction.
The Sn UTA is due to 4p64dn Æ ( 4p54dn+1 + 4dn-14f + 4dn-15p ) (n=0,1,,,9)
transitions.
4f
4d
4p
s
n
io
4f
iat
4d
4p
d
m
a
u
R
Overlapping
of wave function
S
only
4f-excitation
d
n
causes
resonant interaction
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a
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O
among them
st As
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4f and 4pexcitation
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m
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ch
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only 4p-excitation
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
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Opacity effects are important in Sn :
proper pulse duration is required (will be discussed later)
target;
wavelength;
pulse duration :
spot size;
s
a
L
plane Sn foil
1.064 μm (1 beam/normal incidence)
2.2 ns (Gaussian)
660 μmφ
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S
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o 8.0 ns (Gaussian)
480 μmφ
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laser intensity
1011 W/cm2
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Opacity measurement is important (will be discussed later)
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
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Example of radiation spectrum of a body with a temperature
which decreases toward the surface
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1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
22
s
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Features of laser produced high Z plasma,
which consists of two regions.
High density region:
high density / low temperature Corona region : high temperature / low density
/ LTE / b-f absorption
/ CRE / M-, N- band emission
/ isothermal expansion
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h
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2
Sn 1w 1X10 W/cm 2.2ns
1023
60
10
t
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s
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m
aT
u
50
10
R
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8
constant
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10
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n
o
n (x, t) = n e
6
i
t
1
a
r
30
10
v
e
l
laser
e
c
4
c
x
20
10
A
v(x, t) = + c
a
t
m
s
2
10
10
a
Sn target
l
<Z>
P
r
e 10
I = 10 W/cm
s
0
0
a
-50
0
50
100
150
L ns
τ = 2.2
e
e
20
i
19
fluid velocity (X10 6cm/s)
21
ni
Te (eV), <Z>
ion density (cm-3)
22
i
18
L
L
11
2
17
Position (μm)
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
23
0
s
−
x
cst
Most of absorbed energy flux is emitted by radiation, and
EUV (13.5 nm) emission from corona.
10
0.2
19
10
Electron
1018
-0.2
17
10
0.0
-50
L
as
0
50
100
Position (μm)
-0.4
150
1.0
1022
0.5
0.0
-0.5
-1.0
ion density (cm-3)
0.4
1.5
9
0.6
11
2
Sn 1w 1X10 W/cm 2.2ns
1023
2
2
EUV
Radiation
20
t
a
i
d
s
n
io
e
1020
40
vi
30
1019
20
1018
10
1017
-50
0
10
50
i
1021
60
50
100
Position (μm)
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
24
0
150
8
6
4
2
0
fluid velocity (X10 6cm/s)
2.0
EUV flux (X10 W /cm )
ion density (cm-3)
1021
0.8
11
ni
2.5
m
a
u
R
S
d
n
n
a
n
i
a
s
O
n
t
s A
n
o
T
i
t
1
a
r
e
l
e
c
c
A
a
m
s
a
l
P
r
e
Laser
1022
r
e
m
1.0
Energy flux (X10 W/cm )
1023
h
c
S
l
o
o
Te (eV), <Z>
various energy fluxes
in laser ablation
Self–absorption of EUV radiation can not be ignored for tin.
10
10
ni
1022
1019
12
11
1018
s
a
L
1017
-50
10
ion density (cm-3)
1020
11
s
n
io
2
Sn 1w 1X10 W/cm 2.2ns
1023
3
ion density (cm-3)
10
t
a
i
d
m
a
u
10
R
S
d
n
n
a
n
i
a
s
O
t
s A
n
n
o
T
10 ti
1
a
r
e
l
e
c
c
A
10
a
m
s
a
l
P
r
10
e0
50
100
150
13
21
h
c
S
Energy source (W/cm /13.5nm 2%BW)
10
22
r
e
m
14
e
20
10
40
vi
30
1019
20
1018
10
1017
-50
0
50
100
Position (μm)
Position (μm)
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
25
10
50
i
1021
60
0
150
8
6
23
l
o
o
Te (eV), <Z>
EUV ( 2% bandwidth )
emissivity,
self absorption
6
4
2
0
From energy flux conservation in isothermal expansion region,
various loss fluxes and electron temperature can be estimated.
ion density (cm-3)
10
ni
Te
10
1017
-50
40
vi
1020
18
10
50
1021
1019
60
30
8
Te (eV), <Z>
22
2
6
4
l
o
o
corona plasma：
isothermal expansion （density, velocity）
fluid velocity (X10 6cm/s)
11
Sn 1w 1X10 W/cm 2.2ns
1023
r
e
m
h
c
S
−
x t
v( x, t ) = ia+ cs
ad t
x
cs t
ni ( x, t ) = n 0 e
m
u
R
S
d
n
n
a
n
i
a
s
O
t
s A kinetic energy loss flux
1. expansion
n
o
1I = d 1 mv n dx + 1 mcrantci = 3 Z ( n , T ) n T c
dt ∫ 2
2e
l
e
c
2. ionization and internalc
energy loss flux
A
3
⎡
⎤
a
I
= ⎢ Em( n , T ) +
Z ( n , T )T ⎥ n c
2
⎣s
⎦
a
l
P
３. r
radiation energy flux
e
⎞
⎛
s
a
I
j ( n , T ) exp ⎜ − κ ( n , T ) d x ′ ⎟ dxd ν
=
20
2
10
0
50
100
Position (μm)
0
150
s
n
io
0
∞
2
kin
2
s
i
*
0
s
0
e
0
e
s
0
*
ion
L
ion
0
e
0
∞ ∞
rad
∫∫
0 0
e
e
0
s
∞
ν
i
e
⎜
⎝
∫
x
ν
i
e
⎟
⎠
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
26
Dependence of various loss fluxes and electron temperature
(difference of their dependence for Sn and Li)
st
10
10
1
A
sia
kinetic
9
10
10
10
r
e
s
s
a
l
P
S
n
T
e
a
m
11
10
um
10
10
d
n
n
a
O
ionization
n
o
i
t
a
r
e
l
e
c
Ac
10
d
a
R
iat
s
n
io
100
ionization
radiation
9
10
kinetic
9
10
T
e
10
10
10
2
2
laser intensity [W/cm ]
Radiation loss dominates for Sn,
Ionization and kinetic loss
increase at low intensity.
La
l
o
o Li, 20ns
electron temperature [eV]
radiation
r
e
m
2
11
10
h
c
S
loss fluxes [W/cm ]
100
electron temperature [eV]
loss fluxes [W/cm 2]
Sn, 5ns
laser intensity [W/cm ]
Ionization loss dominates at low intensity
and kinetic loss increases at high intensity
for Li.
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
27
Critical Issues and Results to Date in EUV Source Development
h
c
S
l
o
o
- Critical issues
atomic data, conversion efficiency, optimization
r
e
m
t
a
i
d
m
a
u
R
S
d
n
n
a
n
i
a
s
O
t
s A
n
- Further
optimization
o
i
t
1
pulse duration, laser wavelength,
double pulse etc.
a
r
e
l
e
c
- Other problems andcfuture development
A
fast ion, debris
mitigation and target supply
a
m
s
a
l
P
r
e
s
La
- Results to date (optimization of conversion efficiency)
laser, experiments, simulation and modeling
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
28
s
n
io
Research Issues： Understanding of Atomic Processes
materials and transitions for 13.5 nm emission
1.2
Sn
7
6
5+
O 2p-3p
@15.0 nm
5+
O 2p-4d
@12.9 nm
5
Xe
Sn
SnO2 (59%)
SnO2(23%)
1
relative inensity
intensity @ 13.5nm (a.u.)
8
e
m
0.8
rS
ch
LPP_norm
DPP_norm
l
o
o
Li
t
a
i
d
s
n
io
m
a
u
R
S
d
n
n
a
n
i
a
s
O
t
s A
n
o
i
t
1
a
r
e
l
e
c
c
A
Sn: Sn - Sn (4d-4f) a
Xe: Xe (4d-5p)
Li: Ly-α
(many lines 10 ）
(narrow bandwidth)
m （more than 100 lines）
s
a
transitions are not
assigned for Sn and Xe yet
l
P
r
e
s understanding of atomic processes
Importance of atomic data base
a
L
4
5+
O 2p-4p
@11.6 nm
3
5+
O 2p-3d
@17.3 nm
0.6
0.4
6+
O 1s2p-1s7d
@7.9 nm
2
0.2
1
0
0
6
8
10 12 14 16 18 20 22
wavelength (nm)
+8
+14
9
10
11
12
13
14
15
16
17
wavelemgth (nm)
+10
5
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
29
Research Issues： Optimization of LPP – EUV Source
laser energy, intensity and pulse duration
in order to satisfy light source requirement
h
c
s
EUV source power = 350 W/2πsrS
n
r
o
repetition rate
= 10 kHz
i
e
t
a
m
i
d
m
10
a
u
2%
R
S
1 mm sr
d
n
4%
n
a
n
i
a
s
O
2%
understanding
of dependence
t
s
A
n
10
o of the conversion efficiency on
i
4% 1
t
a
・laser intensity and
r
1.7
J
e
l
・pulse duration
0.86 J
e
c
10
c
A
3.3 mm sr
a
m
s
importance of EUV data base
a
l
10
P
r
e1
10
100
s
a
L
laser pulse duration (ns)
12 EUV conversion efficiency
Laser intensity (W/cm2)
l
o
o
optimum laser intensity
to obtain
a maximum conversion efficiency
from laser energy
to EUV radiation energy
of13.5 nm with 2% bandwidth
2
Etendue =
(source size = 700µm)
11
laser energy
10
2
Etendue =
(source size = 1300µm)
9
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
30
d
θ
l
o
o
understanding of dependence
of the conversion efficiency on
・laser intensity (optimum ele. temp.),
・pulse duration (plasma size) and
・laser wavelength (ion density)
Optically thin limit
I EUV(θ) = const
Etendue
≈ 1-3 mm2sr
r
e
m
Optically thick limit
I EUV(θ) = cos(θ)
h
c
S
t
a
i
d
s
n
io
m
a
u
R
S
importance
of EUV data base
d
n
op
n
a
ticn
i
a
1000
a
s
O
0.25 μmlly t
10.6 μm st A 1.06 μm0.53 μm
oo ion
thi
t
τ =20 1 optim
a
ck
r
u
m
10
e
l
de
e
ns
100
c
5
i
tyop
c
dA
tic
e
pth
all
a
yt 2
pr
oo
od
m
s
uc
tha
t
i
n
l
10
P
r
10
10 se
10
10
a
L
ion number density (cm )
multi dimensional expansion
20ns
L
10ns 10 10
5ns
5
5
2ns
2
1ns
17
18
etendue limit
1mm2sr (Ω=π)
plasma scale length (μm)
800-1200 µm
Research Issues： Optimization of LPP – EUV Source
2
1
1
one dimensional expansion
20
19
-3
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
31
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. comparison of theory and exp.
Xe energy levels
Sn energy levels
agreement of theory and exp.
spectra Xe, 13.5 nm
Normalized Intensity
TMU CXS Xe
12.5
13
11+
- He
18
r
e
m
批 : He target
16
披 : HULLAC
13.5
14
14.5
14
12
4d-5p
4d-5f
10
t
a
i
d
13.5nm
8
6
4
6
8
10
12
14
16
18
Wavelength /nm
NIST
HULLAC
Cowan
s
a
L
Grasp
h
c
S
捧 : Xe target
l
o
o
m
a
u
R
S
d
n
n
a
n
i
a
s
O
t
s A
n
o
i
t
1
a
r
e
l
e
c
c
A
a
m
s
a
l
P
r
e
Wavelength / nm
EUVA
4d-4f
Charge state of Xe ions
NIST data Xe 10+
20
12.5 13 13.5 14 14.5
wavelength [nm]
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
32
s
n
io
An ideally “uniform” EUV radiator was produced by GEKKO-XII laser,
to obtain laser intensity dependence of the conversion efficiency
without lateral energy loss and geometrical effects.
spherically uniform plasmas
h
c
S
l
o
o
Laser :
GEKKOXII,
12 beams
wavelength:
ω (1.056 mm)
intensity:
1010 ~ 1012 W/cm2
pulse width: 1.2 ns (FWHM, Gaussian)
r
e
m
t
a
i
d
m
a
u
R
S
d
Target n
chamber
n
a
n
i
a
s
O
t
Target
:
s A
n
o
i
t
1
Sn coated
on a plastic ball
a
r
300~2000 mm ( mostly 700 μm )
e
l
e
c
c
A
Diagnostics (XST: time resolved):
a
m
E-MON ( 13.5 nm 2% bandwidth )
s
a
l
transmission grating (TDI) + CCD
P
er
grazing incident spectrometers (GIS)
f
s
a
L
s
n
io
GXII laser：
12beam、20kJ/1ns
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
33
φ
10 Hz / 10kHz Laser System, Target Chamber for EUV Lithography
6 mm Rod
80 W
r
e
m
h
c
S
l
o
o 2004.6.12 AM2:00
t
a
斜入射回折格子
i
d
m
a
u
R
S
d
n
n
a
n
NFP
i
FFP
a
s
O
t
EUV単色カメラ
s A
n
o
i
t
1 G = 1.45
a
r
e
l
f = 200
e
EUVエネルギーモニター
c
mm
c
A
a
m
s
a
l
P
r
e
s
La
4 mm Rod
30 W
s
n
io
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
34
透過型回折格子
Diagnostics
ion (Thomson parabola)
Slit (500 祄)
monochromatic
EUV mini-calorimeter
neutral particle (LIF)
Spherical
mirror
r
e
m
h
c
S
l
o
o
Back-illuminated
CCD camera
t
a
i
d
m
a
u
R
S
θ
d
n
n
a
n
i
a
s
O
t
s A
n
o
Laser
i
t
1
a
r
e
l
e
c
c
共同利用実験設備
A
a
m
s
a
l
P
r
e
Target
Δλ= 0.057 nm @ 17.3 nm
Δ x = 50 祄
Grating
(1200 grooves/mm)
λ
Schwarzschild
microscope
Mo/Si ML mirrors
filter: Zr/CH
(0.4/0.5祄)
Streak camera
45ٛ
10 ns, 10 Hz
?3 J on target,
Optical
probe
Photo diode
electron density
Interferometer
(interferometer)
Zr/CH filter
s
a
L
Δx = 15 祄
Δt = 2.6 ns
s
n
io
Grazing-incidence
flat field spectrometer
x
E-mon
Δt = 1 ns
Mo/Si ML mirror
Gated CCD camera
t
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
35
x
Conversion efficiency of uniformly irradiated spherical target
target;
laser;
wavelength;
pulse duration :
3.5
Conversion Efficiency(%)
3.0
2.5
2.0
1.5
1.0
0.5
0.0
L
Sn coated spherical CH
Gekko-XII/Nd glass laser/12 beams
1.053 μm
1.2 ns (Gaussian)
r
e
m
h
c
S
l
o
o
m
a
u
R
S
d
n
n
a
n
i
a
s
O
t
s A
n
o
i
t
1
a
r
e
l
e
c
c
A
a
E-mon
m
s
TGS
a
l
P
r
e
as10
10
2
3
4 5 6 7
11
2
10
2
Intensity (W/cm )
Y. Shimada et al.,
Appl. Phys. Lett., 86, 051501 (2005).
3
4 5 6 7
t
a
i
d
12
10
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
36
s
n
io
Comparison of experimental and theoretical EUV spectra for spherical target
IL= 9E+10 W/cm2
IL=3E+11 W/cm2
e
m
1000
500
0
2000
2000
1500
1500
Intensity (a.u.)
Intensity (a.u.)
y(
)
1500
1000
5
10
Wavelength (nm)
15
20
0
t
a
i
d
s
n
io
1000
500
500
0
IL=9E+11 W/cm2
m
a
u
R
S
d
n
n
a
n
i
a
s
O
t
s A
n
o
i
t
1
a
r
simulations
e
l
e
c
c
A
a
m
s
a
l
P
r
e
s
La
experiments
2000
rS
o
h
c
ol
0
0
5
10
Wavelength (nm)
15
20
0
5
10
Wavelength (nm)
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
37
15
20
Opacity of Sn heated by thermal radiation (TR = 50 eV)
has been measured
Schematic of opacity measurement
Sn Opacity
Sn plate
for probing
x-ray source
r
e
m
Thermal radiation
(TR = 50 eV)
h
c
S
Time
Laser inlet hole
l
o
o
m
u
S
n
n
a
n
i
a
s
O
st A
n
o
i
t
1
a
r
e
l
σ
e
c
c
A
a
m
s
a
l
P
r
e
Opacity sample Observation window
(Sn with CH tamper)
Dog-bone gold cavity
t
a
i
dnm
13.5
a
R
d
s
n
io
Wavelength
① Opacity (Sn) ② Self-emission (Sn)
100
TR = (EL/ )1/4
7
6
Time (ns)
Time (ns)
2
3
4
2
3
4
5
5
5
12 14 16 18
10 12 14 (CH)
16 18 ④10
③ Opacity
Self-emission
(CH)
4
1
3
Wavelength (nm)
Time (ns)
Radiation temperature (eV)
8
Time (ns)
L
as
1
1
9
2
3
4
5
2
3
4
5
6 7 8 9
2
3
100
Laser energy (J)
4
Wavelength (nm)
1
2
3
4
5
5 6 7 8 9
1000
10 12
14 16
18
Wavelength (nm)
10 12
14 16
18
Wavelength (nm)
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
38
Theoretical opacity obtained from HULLAC code roughly agrees
with the experiments, but not in detail.
Absorption spectrum of 30-eV tin
1.2
1.0
Transmission
um
Experiment (raw)
Experiment (smooth)
st
0.8
1
0.6
ia
s
A
S
n
0.4
0.2
0.0
8
10
12
P
r
e
m
s
la
14
A
a
16
r
e
m
h
c
S
l
o
o
a
R
d
HULLAC
n
a
On
n
o
i
t
a
r
e
l
e
c
c
t
a
i
d
18
Wavelength (nm)
s
a
L
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
39
s
n
io
Conversion efficiency from laser to EUV emission is obtained
from various loss fluxes determined from power balance.
l
o
o
conversion efficiency
11
10
r
e
m
electron temperature [eV]
loss fluxes [W/cm 2]
100
e
10
9
10
10
10
EUV
EUV , CR
+ I EUV , HD
t
a
i
d
I rad + I ion + I kin
m
I
a
u
T
R
S
I
=
d
n
2
n
a
n
i
a
s
O
t
ionization
s A
n
o
(T )
I
=I
i
t
1
a
r
e
l
kinetic
e
c
c 10
A
10 a
laser intensity
m[W/cm ]
s
a
l
P
r
e
radiation
10
hI
c
ηS =
rad , EUV
EUV , CR
EUV , HD
P , EUV
R
11
2
laser intensity dependences of
various loss flux and
electron temperature
radiation loss dominates
(Sn, n0 = 4x1019 cm-3, 1.2ns)
s
a
L
s
n
io
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
40
2σ T R4 =
I rad
2
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.
l
o
laser intensity dependence of
opower
EUV
h
the conversion efficiency
atcintermediate focus pointns
S
r P = η S I τ εtioR
0.04
e
a
m
i
m
= 280 W a
>d
115 W
u
R
S
0.03
d
n
theory n
n
a
laser intensity
: I = 10 W/cm ,
i
a
s
O
st A
n
pulse
width : τ
= 5 ns,
o
i
t
1
0.02
repetition rate : R = 10 kHz ,
a
r
e
plasma size ( ε = 3 mm str ) :
l
e
c
φ ≈870μm
c
0.01
A
conversion efficiency :
a
from high density
m
η
= 0.03
s
a
l
efficiency of focusing system :
0
P
r
10
10
10
ε
= ε ε ε ε = 0.32
e
s laser intensity (W/cm2)
5/2π, 0.55, 0.9, 0.8
a
L
EUV
conversion effeciency
CEt
CEh
EUV
L
EUV total
11
L
EUV
p
２
t
EUV
10
11
12
total
Ω
R
te
td
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
41
p
2
Electron density obtained from 2d radiation hydrodynamic simulation
agrees well with experiments, which indicates spherical expansion.
2d radiation-hydro
simulation
r
e
m
h
c
S
l
o
o
1D Sim.
2D Sim. with 1D cond.
2D Sim.
m
a
u
R
S
d
n
n
a
n
i
a
s
O
t
s A
n
o
i
t
1
a
r
e
l
e
c
c
A
a
m
s
a
l
P
r
e electron density measurement
t
a
i
d
s
n
io
電子密度干渉計測
0.53-µm (2ω) probe
Target surface
s
a
L
with interference of 2 ω or 4 ω
0
200
400
Distance (µm)
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
42
＠2ω
EUV発光ピーク
＠4ω
Critical Issues and Results to Date in EUV Source Development
h
c
S
l
o
o
- Critical issues
atomic data, conversion efficiency, optimization
r
e
m
t
a
i
d
m
a
u
R
S
d
n
n
a
n
i
a
s
O
t
s A
n
- Further
optimization
o
i
t
1
pulse duration, laser wavelength,
double pulse etc.
a
r
e
l
(theoretical and experimental
works)
e
c
c
A
- Other problemsaand future development
m mitigation and target supply
fast ion,sdebris
a
l
P
r
e
s
La
- Results to date
laser, experiments, simulation and theoretical model
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
43
s
n
io
Further optimization for 1μm laser (Sn : planer target)
Dependence of max. conversion efficiency，optimum pulse duration and
required laser intensity (dotted line) on electron temperature and ion density
h
c
max. CE (solid line; %)
pulse width (solid line：ns) ns
S
r
o
80
i
80
e
t
a
m
i
d
m
a
u
50
R
S
50
d
n
n
a
n
i
a
s
O
t
s A
n
o
30
30 ti
1
a
r
e
l
20
20
e
c
c
A
a
m
s
10
10
a
l
10
10
10
10
10
10
10
10
P
r ion density [cm ]
ion density [cm ]
e
s 1μm laser，max CE = 3 % at 10 -10 W/cm , and 2 ns
a
For
L
electron temperature [eV]
electron temperature [eV]
l
o
o
17
18
19
-3
20 17
10
18
11
19
-3
2
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
44
20
High conversion efficiency was obtained at 2.3 ns pulse duration,
which agrees with theoretical prediction.
l
o
o
Dependence of CE on pulse duration and laser intensity
2.0
m
a
u
R
S
d
n
n
a
n
i
a
s
O
1.5
t
s A
n
o
i
t
1
a
r
e
l
e
c
c
1.0
A
1.2 ns pulse duration
a
m
2.3 ns pulse duration
s
5.6 ns pulse duration
a
l
P
8.5 ns pulse duration
r
e 0.5
Conversion efficiency (%)
s
a
L
r
e
m
h
c
S
10
10
2
3
4 5 6 78
11
2
3
10
Laser intensity (W/cm2)
t
a
i
d
4 5 6 78
1012
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
45
s
n
io
Optimization for different laser wavelength :
absorption lengths of both laser and EUV lights should be comparable.
dependence of absorption lengths of laser and EUV
dotted line：13.5nm absorption length (cm)
Solid line：10.6μm laser absorption length (cm)
optimum density
h
c
S
s
n
io
optimum density
m
u
S
d
n
n
a
n
i
a
s
O
t
s A
n
o
i
t
1
a
r
e
l
e
c
c
A
a
m
s
a
l
P
r
e
10.6 μm
s
a
L
r
e
m
l
o
o
破線：13.5nm EUV (cm)
実線：1.06μm laser (cm)
t
a
i
d μm
1.06
a
R
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
46
Optimum parameters for different laser wavelengths
l
o
o
High density region (1.06μm laser)： high intensity，short pulse
h
c
S
Low density region (10.6μm laser)： low intensity，long pulse
80
t
a
i
d
optimum pulse width (ns)
m 80
a
u
R
S
d
n
n
a
n
i
50
a
s
O
t
s A
n
o
i
t
1
a
r
30
e
l
e
c
c
20
A
a
m
s
a
l
P
10
r
e 10
10
10 10
10
10
electron temperature [eV]
electron temperature [eV]
Max. CE (white solid line：%)
r
e
m
50
30
20
10
1017
L
as
18
ion density
19
[cm-3]
20 17
s
n
io
18
ion density
19
[cm-3]
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
47
1020
Increase of conversion efficiency with double pulses (Miyazaki)
l
o
o
6%
r
e
m
h
c
S
t
a
i
d
m
a
u
R
S
d
n
n
a
n
i
a
s
O
t
s A
n
o
i
t
1
a
r
e
l
e
Experimental conditions,
c
c
Main pulse:
A
1.064 μm/ 10 ns/ 10 -10 W/cm ,
a
m
spot size : 175 μm , 3x10 W/cm
s
a
Pre-pulse:
l
P
532 nm/ 8 ns/ 2x10 W/cm
r
e
Target:
11
φ
s
a
L
s
n
io
12
11
10
T. Higashiguchi et al., APL 88, 201503 (2006)
T. Higashiguchi et al., SPIE 6151, 615145 (2006).
2
2
2
liquid micro-jet with SnO2 (6-17%)
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
48
Research Issues： Mitigation of Fast Ions and Debris
l
o
o
damage of collector mirror by fast ion and neutral atoms
intermediate focus point
r
e
m
h
c
S
development of
・ high replete target supply
・ minimum mass target
t
a
i
d
m
a
u
understanding of
R
S
d
n
・ dependence
of fast ion spectrum
n
a
n
i
a
on laser
parameters and
s
O
t
s A
n
target initial density etc.
o
i
t
1
・ charge exchange and
a
r
e
recombination processes
l
e
c
・ mitigation by such as
c
A
magnetic field
a
m
s
a
l
P
r
e
laser
to irradiation
optical system
ＥＵＶsource
collecting mirror
s
a
L
s
n
io
MD with electron dynamics
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
49
Isothermal expansion with finite target mass causes fast ions.
10-1
10
Present model
(α =1, ε0=1.7 keV)
10-4
10-5
-6
10
10-1
r
e
m
-2
10-3
0
10
1
Maximum ion energy predicted by
the present analytical model
Normalized spectrum dN/dε
Normalized spectrum dN/dε
10
1 0
h
c
S
l
o
o
Maximum ion energy predicted by
the present analytical model
t
a
i
d
Experiment
m
a
u
R
S
d
n
n
a
10
n
i
a
Experiment
s
O
Present model
t
s A
n
(α =3, ε = 3.0 keV)
o
i
t
1
a
10
r
1
10
0.1
1
10
e
l
Ion kinetic energy ε (keV) ce
Ion kinetic energy ε (keV)
c
A
a
m
s
a
l
P
Details can be presented
r
se
on Thursday by Murakami
10-2
-3
0
-4
0.1
Quasi-Planar Expansion
Quasi-Spherical Expansion
100 μm
500 μm
La
10 - 20 μm
レーザー
レーザー
Xe液体ジェット
Sn固体平板ターゲット
1st Asia Summer School on Laser Plasma Acceleration
and Radiation, Beijing, Aug. 7-11, 06
50
s
n
io
Minimum mass target is required to reduce neutral atoms
l
o
o
CE of EUV & emission from neutral atoms vs thickness of Sn
1.5
r
e
m
800
Conversion efficiency (%)
m
a
u
600
R
S
d
n
n
a
n
i
1.0
a
s
O
t
s A
n
o
i
400
t
1
a
r
e
l
e
c
0.5
c
A
200
a
m
s
Emission of Sn
a
l
P
0.0 r
0
e
10
100
1000
as
0+
L
5 6 78
2
3
4 5 6 78
2
3
t
a
i
d
Emission intensity from Sn(I) atoms
EUV-CEs
h
c
S
s
n
io
4 5 678
Sn layer thickness (nm)
1st Asia Summer School on Laser Plasma Acceleration
51
and Radiation, Beijing, Aug. 7-11, 06
PoP 05, 06
Minimum mass target can be realized with use of a droplet target
and punch-out target
Concept
of the
punch-out target
Punch-out
target
Droplet target
prepulse
s
a
L
r
e
m
h
c
S
l
o
o
100
m/s
m
a
u
R
S
d
main
laser
n
n
a
n
i
a
s
O
t
s A
n
o
i
t
1
a
r
e
l
e
c
c
A
a
m
s
a
l
P
r
e
t
a
i
d
1st Asia Summer School on Laser Plasma Acceleration
52
and Radiation, Beijing, Aug. 7-11, 06
s
n
io
Fast ion energy can be reduced for low initial target density
Maximum ion energy
⎛ Λ2 ⎛ Λ2 ⎞ ⎞
1
2
Emax = mi v max ≈ 2 z Te ln⎜⎜ ln⎜⎜ ⎟⎟ ⎟⎟
2
⎝ 2 ⎝ 2 ⎠⎠
2
0
2
2
0
13
0
e R z n0 n
R
Λ = 2 =
∝
λ De
ε 0 Te
Te
2
Nr=
e
m
h
c
S4π
3
l
o
o
R n0 = const
3
0
t
a
i
d
m
a
u
Punch-out target，double pulseScan reduce initial density and fastR
ion energy
d
n
n
a
n
i
a
s
O
t
s A
n
o
i
t
1
a
r
e
l
e
c
c
A
a
m
s
a
l
P
Single pulse
r
e
Dual pulses
s
(Δτ = 100 ns)
La
10 6
Sn 1+
Ion number
Sn 3+
10 5
Punch -out
Sn 1+
Sn 2+
Sn 2+
Static
10 4
10
3
3
4
5 6 7 8 9
2
10 3
Ion energy (eV)
3
4
5 6 7 8 9
□
○
10 4
1st Asia Summer School on Laser Plasma Acceleration
53
and Radiation, Beijing, Aug. 7-11, 06
s
n
io
Mitigation of fast ions by magnetic field
Gyro-radius of fast ions
(2miEmax )
v
R L = max =
ZeB
ωci
12
B=1T
Emax = 10 keV
Z=1
e
m
rS
ch
l
o
o R = 11 cm
s
n
io
L
t
a
i
Stability of expanding plasmaddepends
m
u on B-field configuration Ra
S
d
n
n
a
n
i
a
s
O
t
s A
n
Reduction
of damage by B-field
o
i
t
1
a
r
e
l
e
c
c
A
a
m
s
a
l
P
r
e
Ion signal [a.u.]
1
s
a
L
0.1
0.01
0.001
0.0001
0
0.2
0.4
0.6
0.8
center magnetic field [T]
1st Asia Summer School on Laser Plasma Acceleration
54
and Radiation, Beijing, Aug. 7-11, 06
1
1.2
Summary
l
o
osource can be achieved
I have shown that laser-produced-plasma EUV
h
c
s
for practical use of next generation lithography
S
n
r
o
i
although technical problems, such asedebris mitigation, still remain.
t
a
m
i
d
m
a
u
R
S
d
n
n
a
n
i
a
s
O
t
s A
n
o
i
Understanding
important
1 of fundamental physicsraistalways
for any practical applications.
e
l
e
c
c
A
a
m
s
a
l
P
r
e
s
La
1st Asia Summer School on Laser Plasma Acceleration
55
and Radiation, Beijing, Aug. 7-11, 06
Acknowledgements
l
o
o
Thanks for providing power point files for the lecture, especially
r
e
m
S. Fujioka, M. Murakami, (ILE)
T. Higashiguchi (Miyazaki)
T. Nishikawa (Okayama)
G. O’Sullivan (Dublin)
A. Sunahara,
(ILT)
st
A. Sasaki, (JAEA)
H. Tanuma (TMU)
h
c
S
m
a
u
R
S
d
n
n
a
n
i
a
s
O
A
n
o
i
t
1
a
r
e
l
e
c
c
A
a
m
謝謝 Thank you
for your attention
s
a
l
P
r
e
s
La
t
a
i
d
1st Asia Summer School on Laser Plasma Acceleration
56
and Radiation, Beijing, Aug. 7-11, 06
s
n
io