Imaging in the EUV region

Eberhard Spiller

E. Spiller, June 11, 2008 2

•

Introduction to Imaging•

Applications–Astronomy–Microscopy–EUV Lithography–Direct Reconstruction

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Imaging with light

•

Waves move by λ

in 10-15

to 10-19

sec

•

Wave trains are 10-14

to 10-18

sec long

•

Each wavelet contains less than 1 photon•

Eye responds in about 0.1 sec

•

Everything is washed out !•

How can we see?

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Solutions

1) Use short observation time <10-15 sec need intensity, computer power, sample is destroyed

2) Generate standing waves that last need mirrors, lenses, coherence

3) Use simple objects (crystals): enhanced diffraction peaks low information content

simple reconstruction, resolve atoms

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object Optic

Moving Diffraction pattern

Fast detector → Computer → Image

Standing waves→ Image

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Material properties in the EUV

•

All materials absorb for λ<110 nm•

n = 1 -

δ, no lenses

•

No single surface mirrors, Rmax

< 1%

•

Multilayer designs that minimize absorption can enhance normal incidence reflectance to 70% in the 11 to 14 nm wavelength range

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History of X-Ray Optics bias: high resolution imagesRöntgen, 1895 Shadow graphs, No lenses or mirrorsLaue, 1912 X-ray-diffraction Bragg, 1914 Atomic resolution for crystalsEwald, 1916 Dynamical TheoryCompton, 1923 Grazing incidence mirror, capillaries (1931)Kiessig, 1931 Thin film interference with x-raysDuMond&Youtz, 1935 X-ray peaks from multilayers, diffusion const.Bormann, 1941 Standing wave in crystal reduces absorptionKirkpatrik-Baez, 1948 Imaging with 2 cylinder-mirrors, zone platesWolter, 1952 Imaging with 2 conic sections

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Recent HistoryMöllenstedt,1966 Zoneplates by electron-beamSchmahl, 1969 Zoneplates by holographySpiller, 1972 Multilayers for XUV near normal incidence

telescopes, microscopes, cameras, polarizersSpears, 1972 X-ray lithography (shadowgraphs)Walker, Golub, 1988 XUV telescopes for sun's corona SOHO, TRACEHawryluk, Kinoshita 1988 EUV projection lithographySnigirev 1996 Multi-lensesTinsley, 1998 Figure, finish of mirrors in 1 Å rangeEUVL LLC, 2001 EUVL cameras within diffraction limitFEL for x rays, 2009 Reconstruction in 3-D from diffraction patternsFuture Challenge: Phase contrast for medical x-rays

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Multilayer Mirror Design

1971:Absorber in Node does not absorb100% mirror is possible despite absorption

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O pti c

a b

c

d

f

e

dete

ctor

source

g

Euv/X-ray Imaging Systems

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Normal Incidence Telescopes

1980: Contact Harvard Observatory (L. Golub)

1981: Arcsec resolution with 3”

mirror at 67Å

1986: First launch of Sounding Rockets

1991: Launch of YOHKOH observatory

1995: Launch of SOHO observatory

1998: Launch of TRACE

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Multilayer telescope at IBM

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Properties of IBM system

•

E-beam evaporation low energy minimizes diffusion

•

Ion polishing after deposition smoothes boundaries

•

In situ x-ray reflectivity for immediate quality control

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White Sands Missile Range

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White Sands Recovery

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Trace, 10/10/98, λ=17.1nm

First good photo, 1989

Eclipse on July 11, 1991 gave estimate of scattering from multilayer mirror.

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TRACE, 10/10/98, λ=17.1nm

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Two mirror Schwarzschild for Microscopy and Lithography

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(R. Hudyma)

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Direct Reconstruction

Simple?

Needed:Coherent source (FEL)Many patterns for 3-DObject is destroyed at each exposureInject identical particles, different orientationComputer power and algorithms

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First ExperimentsGraded Multilayer separatesdirect and scattered beamLight from exploding specimen does not reflect.Diffraction patterns of explodingspecimen are obtained and simplespecimen are reconstructed

Diffraction Patterns of Nano Particles injected into the beamhave been recorded and reconstructed

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Challenge: Use phase contrast in medical x-rays

Promise: δ

is 104

times bigger than βEnhanced contrast, less radiation damage

Problem: Small deflection angle, except for very small featuresExperiments with synchrotron radiation and microscopic objects.Interferometry or large distance to detector

Multiple gratings suppress absorption contrast (Pfeiffer 2008)Probable path: Absorption contrast for large features, phase

contrast for small features?

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Figure 1. A portion of the solar corona seen in the Fe IX/X lines at λ=173Å on 7/29/98 from theTRACE spacecraft. Courtesy N AS A/TRACE.