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

0

50

100

150

200

250

300

350

400

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).

1013

1015

1017

1019

1021

0 1000 2000 3000 4000 5000 6000 7000 8000

Sphere A

-20-100102030405060708090100110120130140150

ion

dens

ity (c

m-3

)

Position (μm)

0.0

2.0

4.0

6.0

8.0

10

12

14

0 1000 2000 3000 4000 5000 6000 7000 8000

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

102103104105

106107108109

0 50 100 150 200

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

1016

1017

1018

1019

1020

1021

1022

1023

1024

0.0

5.0

10

15

20

400 600 800 1000 1200 14001600 1800 2000

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

)

20

40

0-50 0 50 10

0time (ns)euspec

-50 0 50 100time (ns)

conv

ersi

on e

ffici

ency

(%)

0

2

4

6

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)

0

10

20

30

40

50

60

70

80

5 10 15 20

spectrumT2-4-0-100ns-200um

2R/Unm

hv(nm) wavelength (nm)10 15 205

EUV

spec

trum

(au)

0

20

40

60

80

0

10

20

30

40

50

60

70

80

5 10 15 20

spectrumT2-4-05-10-100ns-200um

2R/Unm

hv(nm) EU

V sp

ectr

um (a

u)0

20

40

60

80

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

100

50

30

20

10100

50

30

20

10

elec

tron

tem

pera

ture

(eV)

1016 1017 1018 1019 1020

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

100

50

30

20

10100

50

30

20

10

elec

tron

tem

pera

ture

(eV)

1016 1017 1018 1019 1020

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

1013

1015

1017

1019

1021

0 1000 2000 3000 4000 5000 6000 7000 8000

Sphere A

-20-100102030405060708090100110120130140150io

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

5

10

15

20

25

30

35

40

20 30 40 50 60 70 8090100

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

0.0010

0.0012

0.0014

0.0016

10 12 14 16 18 20

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.

106

107

108

109

1010

20 30 40 50 60 70 8090100

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.