Spectral and temporal behaviors of alkali metal vapor extreme ultraviolet sources for

surface morphology applications

Takeshi Higashiguchi1

1 Utsunomiya University, Utsunomiya, Japan 2 JST CREST, Japan 3 University College Dublin, Dublin, Ireland

E-mail: higashi@cc.utsunomiya-u.ac.jp

Mami Yamaguchi1, Takamitsu Otsuka1, Noboru Yugami1,2, Rebekah D'Arcy3, Padraig Dunne3, and Gerry O'Sullivan3

2010 International Workshop on EUV Sources University College Dublin, Belfield, Dublin 4, Ireland Sunday 14 November, 2010, 4:30 PM ‒ 6:00 PM

What’s new

■Observation of the spectra of a potassium plasma

■Evaluation of the multiple charge state ions

■Discussion of the possibility of the hollow cathode mode

Wavelength (nm)

Inte

nsity

(arb

. uni

ts)

20 40 60 80 1000

0.2

0.4

0.6

0.8

1

1.2

Publication

Electromagnetic wave spectrum

D. T. Attwood, “Soft X-Rays and Extreme Ultraviolet Radiation” (Cambridge University Press, Cambridge, 2000)

Capillary discharge-produced plasma extreme ultraviolet (XUV) source

Metal vapor Ar excimer plasma

F. G. Tomasel et al., RSI 79, 013503 (2008). A. El-Habachi et al., APL 72, 22 (1998).

13.2 nm 126 nm

Applications by us

Si SiO2 Remove SiO2 layer

VUV CVD

Cleaning of the grating

Photo-stimulated desorption mass spectrometer using EUV emission

We characterize the capillary discharge-produced plasma XUV source by use of pure

alkali metal vapor.

Objective

■ Observation of spectrum and angular distribution 　è We observe the emission spectra of a potassium plasma.

　è We evaluate the multiple charge state ions by use of the collisional-radiative (CR) model. 　è We discuss the possibility of the hollow cathode mode in a capillary discharge-produced potassium plasma.

Schematic diagram of the experimental apparatus

Emission spectra from the different capillary inner diameters

(a) Inner diameter: 1 mm

(b) Inner diameter: 0.5 mm

Capillary inner diameter dependence of the emission energy

0 0.5 1 1.5 2 2.50

0.2

0.4

0.6

0.8

1

1.2

Capillary diameter (mm)

Inte

nsity

(arb

. uni

ts)

Comparison of experiments and numerical simulation

(a) Experiments

(b) Numerical simulation

Wavelength (nm)

Inte

nsity

(arb

. uni

ts)

20 25 30 35 40 45 50 55 600

0.2

0.4

0.6

0.8

1

1.2

Wavelength (nm)

Inte

nsity

(arb

. uni

ts)

20 25 30 35 40 45 50 55 600

0.2

0.4

0.6

0.8

1

1.2

Numerical simulation

Wavelength (nm)

Inte

nsity

(arb

. uni

ts)

12 eV, 1020 cm-3

20 25 30 35 40 45 50 55 600

0.2

0.4

0.6

0.8

1

1.2

Wavelength (nm)

Inte

nsity

(arb

. uni

ts)

10 eV, 1020 cm-3

20 25 30 35 40 45 50 55 600

0.2

0.4

0.6

0.8

1

1.2

Wavelength (nm)

Inte

nsity

(arb

. uni

ts)

8 eV, 1020 cm-3

20 25 30 35 40 45 50 55 600

0.2

0.4

0.6

0.8

1

1.2

Wavelength (nm)

Inte

nsity

(arb

. uni

ts)

6 eV, 1020 cm-3

20 25 30 35 40 45 50 55 600

0.2

0.4

0.6

0.8

1

1.2

Wavelength (nm)

Inte

nsity

(arb

. uni

ts)

14 eV, 1020 cm-3

20 25 30 35 40 45 50 55 600

0.2

0.4

0.6

0.8

1

1.2

Comparison between experiment and numerical calculation

3d – 3p transitions 3s23pn & 3s23pn-13d1, (3 < n <7)

calculated by Cowan code

40 42 44 46 38 36 34

1.0

0.8

0.6

0.4

0.2

0

Wavelength (nm)

Rel

ativ

e in

tens

ity (a

rb. u

nits

)

Discharge current dependence of time-integrated electron temperature

O2+: λ1 = 70.4 nm O2+: λ2 = 83.4 nm

O3+: λ1 = 55.4 nm O3+: λ2 = 61.7 nm

1 1 2 2ln( )eET

I IΔ

∝λ λ　

Ion population evaluation by use of collisional-radiative (CR) model

( ne = 1020 cm-3 ) CR model

Population ZZ

kk 1

n

n=

=

∑

α α=

+ + +e+1

r e e 3b e

( , )( 1, ) ( 1, )

Z

Z

S Z Tnn Z T n Z T

Comparison between DPP and LPP at electron temperature of 12 eV

Time-integrated spectra from a capillary discharge-produced plasma (a) and from a Nd:YAG laser-produced plasma (b) at the laser intensity of 2 × 1010 W/cm2 with a focal spot size of 250 µm (FWHM).

20 30 40 50 600

0.2

0.4

0.6

0.8

1

1.2

20 30 40 50 600

0.2

0.4

0.6

0.8

1

1.2

Wavelength (nm)

Inte

nsity

(arb

. uni

ts)

Wavelength (nm)In

tens

ity (a

rb. u

nits

)(a) (b)

Discharge current dependence of the XUV conversion efficiency

I-V dependence: Possibility of hollow cathode mode

A. El-Habachi et al., APL. 72, 22 (1998).

Angular distribution of the XUV emission energy

-1tan

170

rl

=

;

θ

mrad

divergence 150 mrad

Target

θ

Ion population of multi-charged potassium ions

Experimental and numerical spectra of a laser-produced K plasmas

Temporal history of the 39-nm XUV emission from a LPP

Summary

We observed the capillary discharge-produced plasma XUV emission by use of pure alkali

metal vapor.

■ Observation of spectrum and angular distribution 　è We observed the emission spectra of a potassium plasma.

　è We evaluated the multiple charge state ions by use of the collisional-radiative (CR) model. 　è We discussed the possibility of the hollow cathode mode in a capillary discharge-produced potassium plasma.

EUV semiconductor lithography

Two ways for efficient EUV sources: LPP & DPP EUV sources

EUV source at 13.5 nm

Applied Physics Letters 86, 231502 (1-3) (2005). Applied Physics Letters 88, 161502 (1-3) (2006). Applied Physics Letters 88, 201503 (1-3) (2006). Applied Physics Letters 90, 191503 (1-3) (2007). Applied Physics Letters 91, 151503 (1-3) (2007). Applied Physics Letters 91, 231501 (1-3) (2007). Applied Physics Letters 92, 181503 (1-3) (2008). Applied Physics Letters 92, 211503 (1-3) (2008).

-200 0 200 400 6000

0.5

1

1.5

O+

O2+

Sn+

Sn2+

00 5 10 15 20

5

10

15

運動エネルギー (keV)

イオン信号

(任意単位

)

二重パルスの遅延時間 (ns)

軟X線変換効率

(%)

運動エネルギー (keV)

00 5 10 15 20

5

10

15

イオン信号

(任意単位

)

プリパルス有

プリパルス無

プリプラズマの生成により，スズイオンのエネルギーおよびイオン信号量が減少した

プリパルス無

プリパルス有

プリプラズマの生成により，軟X線出力が3倍増加した．

Laser

Plasma Blow-Off

Hot Dense Plasma

Liquid JetDroplet

EvaporationSuprathermalCharged Particles

Ions, Electrons

RadiationVisible, UV, DUV, Soft X-Ray

np, Te, Z