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Recent Advances in Development and Application of Compact Laser Plasma

Soft X-ray Sources based on a Gas Puff Target

Henryk Fiedorowicz, Andrzej Bartnik, Przemysław Wachulak, Karol Janulewicz,

Roman Jarocki, Jerzy Kostecki, Tomasz Fok, Łukasz Węgrzyński

Institute of Optoelectronics

Military University of Technology

Warsaw, Poland

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https://www.euvlitho.com/2015/S3.pdf

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Outline

Introduction

- soft X-rays and extreme ultraviolet (EUV)

- laser plasma soft X-ray/EUV source

- gas puff target approach

Source applications

- EUV metrology

- EUV and soft X-ray imaging,

- EUV processing material,

- EUV photoionization studies,

- soft X-ray radiobiology,

- soft X-ray absorption spectroscopy (NEXAFS)

- soft X-ray optical coherence tomography (X-OCT)

Conclusions

Henryk Fiedorowicz, Andrzej Bartnik, Karol Janulewicz, Przemysław Wachulak

Roman Jarocki, Jerzy Kostecki, Mirosław Szczurek,

Daniel Adjei, Inam Ul Ahad, Mesfin Ayele, Tomasz Fok, Martin Duda, Ismail Saber,

Alfio Torrisi, Łukasz Węgrzyński

Laser-Matter Interaction (LMI) Group

Research goals: Development of laser-driven sources of X-rays and EUV

for application in science and technology

http://www.ztl.wat.edu.pl/zoplzm/

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Introduction

Nanowaves

Soft X-rays (XUV) 0.1 λ < 10 nm

Extreme Ultraviolet (EUV) 10 λ < 121 nm (He Lyman-alpha)

Motivations

- nanometer resolution (nanolithography & nanoimaging)

- nanometer penetration depth (processing of surfaces & nanoanalysis)

- elemental mapping (nanoscale)

Generation

- synchrotrons, FELs

- plasma sources (discharge plasmas, laser plasmas)

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ISO International Standard 21348 http://www.spacewx.com/ISO_solar_standard.html

Introduction

Focusing

lens

Vacuum

chamber

Laser system (ns, J)

Oscillator Amplifier Target system solid, liquid, gas

Soft X-rays & EUV Laser plasma

Ne 1019 – 1022 cm-3

Te 50 – 500 eV Nd:glass

Nd:YAG

KrF

CO2

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Source characteristics

- high single-pulse brightness

- short-pulse duration

- easy tuning of wavelength

- low investment costs

Main disadvantages

- laser target operation

- target debris production

Schematic of laser plasma soft X-ray/EUV source

Introduction

outer nozzle inner nozzle

high-Z gas

(xenon, krypton, argon)

low-Z gas

(helium,

hydrogen) laser beam

electromagnetic valve system

schematic of a double-str eam gas puff target

X-ray backlighting images

Fiedorowicz et al. Appl. Phys. B 70 (2000) 305; Patent No.: US 6,469,310 B1 8

Double-stream gas puff target

Comparison with solid targets

8 10 12 14 16 180

10000

20000

30000

40000

50000

inte

ns

ity,

CC

D c

ou

nts

xenon gas puff

solid copper

inte

ns

ity,

CC

D c

ou

nts

8 10 12 14 16 180

10000

20000

30000

40000

50000

inte

ns

ity,

CC

D c

ou

nts xenon gas puff

solid iron

8 10 12 14 16 180

10000

20000

30000

40000

50000

wavelength, nm

xenon gas puff

solid tin

inte

ns

ity,

CC

D c

ou

nts

wavelength, nm

8 10 12 14 16 180

10000

20000

30000

40000

50000

EUV Emission from a Double-Stream Xenon/Helium Gas Puff Target Irradiated with a Nd:YAG Laser

wavelength, nmwavelength, nm

xenon gas puff

solid aluminium

• EUV emissions from various solid and an xenon gas puff targets irradiated with

a Nd:YAG laser (0.5J/10ns)

- Elimination of debris

- Operation with repetition

- Conversion efficiency improvement Gas puff target

Fiedorowicz et al. Opt. Commun. 184 (2000) 161 9

ILE

Osaka

Laser systems

We use commercial nanosecond Nd:YAG lasers

EKSPLA Compact Flash-Lamp Pumped

Q-switched Nd:YAG Lasers

NL300 Series

4 ns/0.8 J/10 Hz

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EKSPLA High-Energy Flash-Lamp Pumped

Q-switched Nd:YAG Lasers

NL310 Series

1-10 ns/10 J/10 Hz

Quantel High-Energy Pulsed Nd:YAG

Lasers

YG980 Series

8-11 ns/2.5 J/10 Hz

Compact laser plasma EUV source

compact laser-plasma EUV source based on a gas puff target irradiated with

a commercial Nd:YAG laser (4 ns/0.5 J/10 Hz) was developed for EUV metrology

EUV lamp

EUV metrology setup

Fiedorowicz et al. J. Alloys & Comp. 401 (2005) 99

10 cm

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EUV source parameters

-0.6 -0.4 -0.2 0.0 0.2 0.4 0.6

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

0

50.00

100.0

200.0

300.0

350.0

400.0

500.0

600.0

Z Axis (mm)

Y A

xis

(m

m)

Spectral image at 13.5 nm

400 m

EUV spectrum

9 10 11 12 13 14 15

10000

20000

30000

40000

50000xenon gas puff target

Nd:YAG laser (4ns; 0.5J)

tXe

=800s, tH=400s

Inte

nsity (

CC

D c

ou

nts

)

Wavelength, nm

CE at 13.5 nm

1.5 - 2 %

0 5 10 15 20 25 30 35

0.000

0.005

0.010

0.015

5 ns

Am

plit

ud

e, V

Time, ns

Time profile

Fiedorowicz et al., J.Alloys&Comp. 401 (2005) 99

Rakowski et al. Appl. Phys B 101 (2010) 773 12

Laser plasma soft X-ray source

Laser parameters 0.8J, 4ns, 10Hz

Gas (argon or nitrogen) pressure 10 bar

Wavelength range

2.5-4nm

Photon number in 4

3.51014 /pulse

Photon energy in 4

28.1mJ/pulse

Wavelength

2.88nm

Photon number in 4

5.61013 /pulse

Photon energy in 4

3.9mJ/pulse

Wachulak et al. Nucl. Instr. Meth. (2010)

Argon

Nitrogen

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wavelength [nm]

nitrogen

oxygen

argon

xenon

krypton

Soft X-ray spectra

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X-ray absorption fine structure (XAFS) spectroscopy

X-ray absorption fine structure (XAFS) spectroscopy is a technique to probe the local

structure of matter by studying the oscillations above the X-ray absorption edge.

A typical XAFS spectrum exhibits two energy regions: the near-edge region (NEXAFS or

XANES) and the extended one (EXAFS).

The NEXAFS is more sensitive to the electronic structure, while the EXAFS gives more

information on bond distances, coordination numbers and local disorder.

NEXAFS is also very sensitive to the bonding environment of the absorbing atom.

over 500 participants 15

Near-edge X-ray absorption fine structure (NEXAFS)

The NEXAFS technique is usually performed at synchrotron radiation sources.

XPS/NEXAFS endstation installed on HE-SGM beamline at BESSY II

However, compact laboratory NEXAFS systems have been developed.

Laser-Laboratorium Gottingen Institut für Optik und Atomare Physik

Technical University Berlin

Institute of Optoelectronics

Military University of Technology, Warsaw

5.9 m

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Compact system for NEXAFS spectroscopy

Compact system for near-edge X-ray absorption fine structure (NEXAFS) spectroscopy has been

developed using a laser plasma soft X-ray source based on a gas puff target

Schematic of the NEXAFS system Experimental setup of the NEXAFS system

Typical reference and sample

spectra for a 1 m thick PET foil

Attenuation coefficient

near the carbon K- edge

NEXAFS spectrum for a 1

m thick PET sample

Wachulak et al. Optics Express 26, 8260 (2018)

Elem

ent

Mea

sure

d [%]

Theo

retic

al

[%]

C 65.9 62.5

H 4.8 4.2

O 29.3 33.3

Elemental

composition

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2-D elemental mapping with NEXAFS

2-D elemental mapping of an EUV-irradiated PET sample was demonstrated using a compact

NEXAFS spectromicroscopy system with a laser plasma soft X-ray source based on a gas puff target

Schematic of the NEXAFS spectromicroscopy system

2-D composition maps for carbon, hydrogen and oxygen

NEXAFS spectrum for a 1 m thick PET

sample (pristine and EUV-modified)

Wachulak et al. Spectrochimica B 145, 107 (2018)

Modification of PET with EUV

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Single-shot NEXAFS spectroscopy

Experimental setup for the single-shot NEXAFS spectroscopy

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inte

nsity [a

.u.]

energy [eV]

krypton (reference)

spectrum

System parameters:

NL129 (Ekspla) laser system:

E=10 J, t=1 ns

1 shot , NEXAFS spectrum acquisition

Kr-11bar, He-5bar pressure

Sample: 1mm thick PET

Wachulak et al., Materials 11, 1303 (2018)

Martin Duda

Poster – P24

Single-shot NEXAFS spectroscopy

Single-shot NEXAFS spectroscopy results for PET sample

20 Wachulak et al., Materials 11, 1303 (2018)

Single-shot PET NEXAFS spectrum

* Dhez, O. et al., J. Electron. Spectrosc. Relat.

Phenom. 128, 1 (2008)

*

Spectral component assignment

Sample PET foil 1 mm thick (C10H8O4)n

Method Composition [%] Global error [%]

C H O

Theoretical w/w % 62.5 4.2 33.3 0

Experiment 10% step for each peak 67.6 3.8 28.6 2.3

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Optical coherence tomography (OCT)

Optical coherence tomography (OCT) is a well-known imaging technique that uses

coherent light to capture micrometer-resolution, two- and three-dimensional images

from optical scattering media. Images are created from reflections of the light.

The axial resolution of OCT is in the order of the coherence length of a light source lc

which depends on the central wavelength λ0 and the spectral width (FWHM) of the

source ΔλFWHM.

OCT with broadband visible and near-infrared sources typically reach axial (depth)

resolutions in the order of a few micrometers.

G. Paulus & Ch. Rödel „Short-wavelength coherent tomography”

US Patent No.: US 7,656,538 B2

For Gaussian shaped spectrum

the coherence length is defined:

The axial resolution improvement has been proposed by extention of optical coherence

tomography (OCT) to the short-wavelength coherent tomography (XCT) using

extreme ultraviolet and soft X-rays.

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X-ray coherence tomography (XCT)

Realizing a classical Time-domain XCT (TD-XCT) using a Michelson interferometer

is highly demanding because of problems with optics.

In order to overcome these problems, the use of a variant of Fourier-domain XCT

(FD-XCT) setup has been proposed.

A schematic of the proposed FD-XCT setup:

The probing beam is reflected at the layer surfaces of the sample. The beams

interfere and cause a modulated reflected spectrum that can be measured with a

grating spectrometer.

The toroidal mirror images the sample surface onto the CCD camera. The reference

wave and the sample wave share the same path. Moreover, using this variety of

XCT, a beam splitter can be completely avoided.

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XCT using synchrotron radiation

A proof-of-principle experiment and the first demonstration of XCT has been recently

performed at synchrotron radiation sources at DESY (Deutsches Elektronen-

Synchrotron) and BESSY (Berliner Elektronenspeicherring-Gesellschaft fur

Synchrotronstrahlung).

5 nm Au

Si

Sketch of the sample 3-D XCT image of a silicon-based sample

with different buried layers of gold

The depth structure was reconstructed by analyzing the

spectral interferogram.

Lateral imaging was achieved by scanning the focused

beam over the sample with a lateral resolution of 200 μm

As XCT exploits the surface reflection as a reference,

the sketch on right of the picture shows the sample

how it is expected to be measured.

S. Fuchs, Ch. Rödel, A. Blinne, U. Zastrau, M. Wünsche, V. Hilbert, L. Glaser, J. Viefhaus, E. Frumker, P. Corkum, E. Förster &

G.G. Paulus, Nanometer resolution optical coherence tomography using broad bandwidth XUV and soft x-ray radiation,

Scientific Reports 6, 20658 (2016)

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XCT using synchrotron radiation

(a) Recorded reflected spectral intensity for EUV (40–12 nm) of the layer system (c). The blue dots

correspond to the CCD-cameras pixels the red curve is the interpolation.

(b) Reconstructed depth profile: The two gold layers appear clearly separated, thus the resolution is

better than 18 nm.

(d) Recorded reflected spectral intensity for soft X-rays (4.4–2.3 nm) of the layer system (f). The blue

dots correspond to the energy measurement discretization and the red curve is the interpolation.

(e) Reconstructed depth profile: The front and backside of the platinum layer appear separated, thus the

resolution is better than 8 nm.

XCT signals for EUV and soft X-ray radiation

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XCT using laser plasma soft X-ray source

Schematic of the XCT setup

Soft X-ray spectrum

Experimental arrangement of the XCT setup

CCD

camera

Grating

spectrograph Laser plasma

soft X-ray source

Sample

chamber

Nd:YAG

laser

Sample (Mo/Si mirror)

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XCT using laser plasma soft X-ray source

(a) measured reflectivity of the Mo/Si

multilayer structure in the wavelength

range from 1.5 nm to 5.5 nm.

(b) k-space reflectivity spectrum with a

Gaussian-type window applied

(c) reconstruction of a depth information

from the Mo/Si structure, experimental

data (bottom, pink curve) and simulation

(top, blue curve).

(d) visualization of depth structure of the

sample; a comparison between

theoretical and experimental data.

Axial spatial resolution was estimated.

The FWHM of the peak, related to the first

Si-Mo interface equals to ~2 nm. Taking into

account another, well defined experimental

spectral peak at 30 nm depth, the FWHM is

estimated to be ~2.6 nm.

The axial spatial resolution in XCT can be

comparable to FWHM values and is of the

order of 2–2.6 nm.

Results of the preliminary XCT measurements

P. Wachulak, A. Bartnik, H. Fiedorowicz,

Optical coherence tomography (OCT) with 2 nm axial

resolution using a compact laser plasma soft X-ray source

Scientific Reports 8, 8494 (2018)

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XCT setup for 3-D imaging

Optical scheme of the XCT setup for 3-D imaging using a laser plasma light source

Optics and system parameters:

length of the optics d = 100.00 mm

object-image distance x = 800.00 mm

magnification = 4.3333

angle = 11.51 deg,

object distance x = 100.00 mm

image distance y = 600.00 mm

critical angle = 2.58 deg

Ellipsoidal mirrors parameters:

A = 400.177 mm, B = 11.906 mm

din = 15.759 mm, dout = 20.625 mm

NAin = [0.0786, 0.0515],

NAout = [0.0172, 0.0113

Detection system:

grating width = 2.0 mm,

grating period = 200.0 nm

grating - CCD distance z = 58.18 mm

CCD chip size = 13.0 mm,

number of pixels = 1024×1024

max wavelength = 22.2 nm,

dispersion = 0.043 nm/pix

source size = 0.10 mm,

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XCT setup for 3-D imaging

Schematic of the XCT setup for 3-D imaging using a laser plasma light source

Experimental vacuum

chamber

Nd:YAG laser system

Nd:YAG laser

(1.6 J, 6-10 ns, 20 Hz)

Summary

compact laser plasma EUV and soft X-ray sources based on

a gas puff target have been developed,

the sources were used in metrology of EUV optics, EUV and

soft X-ray microscopy, EUV and soft X-ray pulsed radiography,

EUV processing materials, EUV photoionization studies, and

soft X-ray radiobiology,

application in soft X-ray absorption spectroscopy (NEXAFS),

soft X-ray optical coherence tomography has been recently

demonstrated,

new techniques based on a laser plasma soft X-ray and EUV

sources are ready for the use in ”real” research.

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Acknowledgements

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Funding

The research was supported by the Ministry of Science and Higher Education of

Poland (EUREKA project E! 3892 ModPolEUV and COST Action MP0601 project),

the Foundation for Polish Science (HOMING 2009 Programme), the National Centre

for Research and Development (LIDER Programme), the National Centre of Science

(Beethoven Programme) and the European Comission (Laserlab Europe, EXTATIC,

CEZAMAT and OPTOLAB projects).

Collaboration

Gerhard G. Paulus, Silvio Fuchs, Christian Rödel, Martin Wunsche, Johann Abel

(Institute of Optics and Quantum Electronics, Jena University, Germany)

http://www.ncbir.pl/