Professor David Attwood, UC Berkeley
EUV and Soft X-Ray Optics

EUV and Soft X-Ray Optics
David Attwood
University of California, Berkeley

Cheiron SchoolSeptember 2012
SPring-8
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The short wavelength region of the electromagneticspectrum

n = 1 –  + i,  << 1
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Professor David Attwood, UC Berkeley
EUV and Soft X-Ray Optics

Available x-ray optical techniques

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Basic ionization and emission processes
in isolated atoms

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EUV and Soft X-Ray Optics

Energy levels, absorption edges, and characteristic lineemissions for a multi-electron atom

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Energy levels, quantum numbers, andallowed transitions for the copper atom

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Professor David Attwood, UC Berkeley
EUV and Soft X-Ray Optics

Refractive index from theIR to x-ray spectral region

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Refractive index at nanometer wavelengths

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Professor David Attwood, UC Berkeley
EUV and Soft X-Ray Optics

Refractive index in the soft x-ray
and EUV spectral region

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9Photoionization and electron binding energies

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Professor David Attwood, UC Berkeley
EUV and Soft X-Ray Optics

Available x-ray optical techniques

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Diffractive and reflective optics for EUV,
soft x-rays and hard x-rays

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Professor David Attwood, UC Berkeley
EUV and Soft X-Ray Optics

Diffractive optics for soft x-rays and EUV

Zone Plates

Gratings

PinholesCheironSchool_Sept2012_Lec1.ppt

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Diffraction from a transmission grating

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Professor David Attwood, UC Berkeley
EUV and Soft X-Ray Optics

A Fresnel zone plate lensCheironSchool_Sept2012_Lec1.ppt

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A Fresnel zone plate lens used as a diffractive lens forpoint to point imaging

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Professor David Attwood, UC Berkeley
EUV and Soft X-Ray Optics

Depth of focus and spectral bandwidth

CheironSchool_Sept2012_Lec1.ppt

17A Fresnel zone plate lensfor soft x-ray microscopy

Courtesy of E. Anderson, LBNL
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Professor David Attwood, UC Berkeley
EUV and Soft X-Ray Optics

Zone plates for ALS STXM beamlines –“3D Engineered Nanostructures”
r = 35 nm, t = 180 nm Au, N = 1700
D = 240 m, 3 x 95 mD central stop

Outerzone
close-upOuter zones

Inner zones

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The Nanowriter: high resolution electron beam
writing with high placement accuracy

Courtesy of E. Anderson (LBNL)
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Professor David Attwood, UC Berkeley
EUV and Soft X-Ray Optics

Zones plates for soft x-ray image formation

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New x-ray lenses: Improving contrast and resolution
for x-ray microscopy

C. Chang, A. Sakdinawat, P.J. Fischer, E.H. Anderson, D.T. Attwood, Opt. Lett. 2006; Sakdinawat and Liu, Opt. Lett. 2007;
Sakdinawat and Liu, Opt. Express 2008
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Professor David Attwood, UC Berkeley
EUV and Soft X-Ray Optics

Diffraction limited x-ray imaging
Diffraction limited imaging is limited by the finite
wavelength and acceptance aperture:rresol. = k1  / NA

where NA = n sin and the constant k1 depends onillumination and specific image modulation criteria.
For x-rays
n = 1 –  + i,  << 1
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Diffraction limited x-ray imaging
For example, the widely accepted Rayleigh criteria for resolving twoadjacent, mutually incoherent, point sources of light, results in a 26%
intensity modulation.
 = 2.48 nm(500 eV)Two overlapping
Airy patterns

rresol. = 0.61  / NA

Note: Other definitions arepossible, depending on theapplication and the ability todiscern separated objects.

Resultant intensity pattern when
the two point sources are “justresolved”, such that the central
lobe maximum due to one point
source overlaps the firstminimum (dark ring) of the other.
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2412Professor David Attwood, UC Berkeley
EUV and Soft X-Ray Optics

Resolution and illumination
Achievable resolution can be improved by varying illumination:
An object pattern ofperiodicity d diffracts
light and is just capturedby the lens – setting
the diffraction limited
resolution limit.

Diffraction from an
object of smaller
periodicity, d/2, is justcaptured, and resolved,
when illuminatedfrom an angle.

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Resolution, illumination, and optical transfer function

Spatial frequency response of the optical system can be optimized by tailoring
the angular distribution of illumination.

=NAcondNAobj(10.3)

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Professor David Attwood, UC Berkeley
EUV and Soft X-Ray Optics

 = 1.52 nm (815 eV)
r = 15 nm
N = 500
D = 30 m
f = 300 m
 = 0.38
0.8 r = 12 nm

Cr/Si test pattern (Cr L3 @ 574 eV)
4 ph/pixel)
27(2000 X 2000, 10
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Hard x-ray zone plate microscopy• Shorter wavelengths, potentially better spatial
resolution and greater depth-of-field.
• Less absorption (); phase shift () dominates,higher efficiency.
• Thicker structures required (e.g., zones), higher
aspect ratios pose nanofabrication challenges.
• Contrast of nanoscale samples minimal; will require
good statistics, uniform background, dose mitigation.

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EUV and Soft X-Ray Optics

Nanoscale hard x-ray tomography
X-ray Zone-plate Lens

Challenges for achieving nm scale resolution:• High resolution objective lens: limiting the ultimate resolution• High numerical aperture condenser lens:• Detector: high efficiency for lab. source and high speed for synchrotron sources• Precision mechanical system
Courtesy of Wenbing Yun and Michael Feser, Xradia

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Xradia nanoXCT: Sub-25 nm Hard X-ray Image
Xradia Resolution Pattern• 50 nm bar width• 150 nm thick Au• 8keV x-ray energy• 3rd diffraction order

F. Duewer, M. Tang,
G. C. Yin, W. Yun,
M. Feser, et al.

Xradia nano-XCT
8-50S installed atNSRRC, Taiwan

400 nm30

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Professor David Attwood, UC Berkeley
EUV and Soft X-Ray Optics

Hard x-ray imaging based on glancing incidence
reflective optics• Optics behave differently at these very short wavelengths(nanometers rather than 520 nm green light)• The refractive index is less than unity, n = 1 –  + i• Waves bend away form the normal at an interface• Absorption is significant in all materials and at all wavelength.
• Because of absorption, refractive lenses do not work, prisms donot, windows need to be extremely thin (100 nm or less).
• Because light is bent away from the surface normal, it possible tohave “total external reflection” at glancing incidence – a commonlyused technique.
• Kirkpatrick-Baez (KB)
mirror pair

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Glancing incidence optics

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Professor David Attwood, UC Berkeley
EUV and Soft X-Ray Optics

Total external reflection with finite CheironSchool_Sept2012_Lec1.ppt

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Normal incidence reflection at an interface

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Professor David Attwood, UC Berkeley
EUV and Soft X-Ray Optics

Focusing with curved glancing incidence optics

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Fluorescent microprobe based in crossedcylinders

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EUV and Soft X-Ray Optics

High resolution x-ray diffraction under high pressure using
multilayer coated focusing optics

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X-ray microprobe at SPring-8
Optical microscope
PIN photodiodemm
f1: 252m

m
f2: 15098m
45m

Undulator

DCM
TC1Slit

Mirror manipulator
Ion chamber
Incident Slit

SDDBeam monitor
Sample & Scanner

Experimental hutch

2006

Front end

Courtesy of K. Yamauchi andH. Mimura, Osaka University.
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Professor David Attwood, UC Berkeley
EUV and Soft X-Ray Optics

A high quality Mo/Si multilayer mirror
N = 40d = 6.7

Courtesy of Sasa
ˇ Bajt (LLNL)

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Scattering by density variations within a multilayer
coating

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Professor David Attwood, UC Berkeley
EUV and Soft X-Ray Optics

Multilayer mirrors satisfy the Bragg condition

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Multilayer mirrors satisfy the Bragg condition

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Professor David Attwood, UC Berkeley
EUV and Soft X-Ray Optics

High reflectivity, thermally and environmentally robust multilayer
coatings for high throughput EUV lithography

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Atomic scattering factors for silicon (Z = 14)

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Professor David Attwood, UC Berkeley
EUV and Soft X-Ray Optics

Atomic scattering factors for molybdenum (Z = 42)

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CXRO Web Site

X-Ray Interactions with Matter . Search CXRO

Facilities. About CXRO

www.cxro.LBL.gov/Publications
ResearchX-Ray Tools
Visitors
Personnel
Comments?
Server Stats• Atomic scattering factors• EUV/x-ray properties of the elements• Index of refraction for compound materials• Absorption, attenuation lengths, transmission• EUV/x-ray reflectivity(mirrors, thin films, multilayers)• Transmission grating efficiencies• Multilayer mirror achievements• Other

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Professor David Attwood, UC Berkeley
EUV and Soft X-Ray Optics

Sputtered deposition of a multilayer coating

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Multilayer coatings – “1D nanostructures”
Eric Gullikson, Farhad Salmassi,Yanwei Liu, Andy Aquila (grad),Franklin Dollar (UG)

World reference standard

Creating uniformity for/50 optics

Wide band, narrow band,and chirped mirrors
for fsec applications

Reflectance (%)

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Cr/Ti: 17%

Ti 2p

15

CX050622B
Cr/Ti
=81.5 deg
d=1.384 nm
N=400
=0.35 nm

10ReflectanceWorld record inwater window

50445

450

455

460

Photon energy (eV)CheironSchool_Sept2012_Lec1.ppt

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Professor David Attwood, UC Berkeley
EUV and Soft X-Ray Optics

Broad bandwidth mirrors
needed for as/fs pulses   •Multilayer mirrors depend on
constructive interference fromindividual interfaces•Higher reflectivity needs morelayers•Bandwidth gets narrower withmore layers

Attosecond pulse Broad bandwidth Limited number of layers

N<10 layers required for
200 as pulse (@13nm)

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Aperiodic multilayers for asec application
Optimizing multilayers for specificapplications requires the use ofsimulation of a multilayer stack withvariations in the thickness of eachmaterial in the multilayer.

Successful design of aperiodic
multilayers requires:
1. EM wave in multilayer
structure
2. Optimization Algorithm
3. Sample preparation
4. Verification

A. L. Aquila, F. Salmassi, F. Dollar, Y. Liu, and E. Gullikson, "Developments in realistic design foraperiodic Mo/Si multilayer mirrors," Opt. Express 14, 10073-10078 (2006)
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Professor David Attwood, UC Berkeley
EUV and Soft X-Ray Optics

The Cassegrain Telescope with multilayer coatings for
EUV imaging of the solar corona

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Multilayer Laue Lens for focusing hard x-rays

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Professor David Attwood, UC Berkeley
EUV and Soft X-Ray Optics

Photon energy, wavelength, power

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Lectures online at www.youtube.com

Amazon.com

UC Berkeley
www.coe.berkeley.edu/AST/sxreuv
www.coe.berkeley.edu/AST/srms
www.coe.berkeley.edu/AST/sxr2009

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