laser produced plasma for euv radiation sources on asian

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


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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- 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 ]



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)

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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

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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)

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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

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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.

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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 ]



radiationT

e

ionization

kinetic

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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

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

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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.

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- 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

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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

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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

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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

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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

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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)

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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

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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

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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

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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

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⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎟⎠

⎞⎜⎜⎝

⎛ 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+

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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

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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.

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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

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laser produced plasma for euv radiation sources on asian

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