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

Cheiron School
September 2013
SPring-8
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The short wavelength region of the electromagneticspectrum

n = 1 – δ + iβ

δ, β << 1
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Available x-ray optical techniques

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Basic ionization and emission processes
in isolated atoms

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

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

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Refractive index from theIR to x-ray spectral region

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Refractive index at nanometer wavelengths

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

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Photoionization and electron binding energies

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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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Diffractive optics for soft x-rays and EUV

Zone Plates

Gratings

PinholesCheironSchool_Sept2013_Lec1.ppt

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Diffraction from a transmission grating

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A Fresnel zone plate lensCheironSchool_Sept2013_Lec1.ppt

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

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Depth of focus and spectral bandwidth

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A Fresnel zone plate lensfor soft x-ray microscopyCourtesy of E. Anderson, LBNL
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Zone plates for ALS STXM beamlines –“3D Engineered Nanostructures”
Δr = 35 nm, Δt = 180 nm Au, N = 1700
D = 240 µm, 3 x 95 µmD central stop

Inner zones

Outerzone
close-upOuter 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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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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Diffraction limited x-ray imaging
Diffraction limited imaging is limited by the finite
wavelength and acceptance aperture:
Δrresol. = k1 λ / NA

where NA = n sinθ and the constant k1 depends onillumination and specific image modulation criteria.
For x-rays
n = 1 – δ + iβ

δ, β << 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.
λ = 2.48 nm(500 eV)Two overlapping
Airy patterns

Δrresol. = 0.61 λ / 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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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.

σ=NAcondNAobj(10.3)

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λ = 1.52 nm (815 eV)
Δr = 15 nm
N = 500
D = 30 µm
f = 300 µm
σ = 0.38
0.8 Δr = 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 (β); phase shift (δ) 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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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 at
NSRRC, Taiwan

400 nm30

New	  ultra	  high	  aspect	  ra0o,	  high	  eﬃciency,	  hard	  x-­‐ray	  zone	  plates	  for	  high	  spa0al	  resolu0on	  at	  30-­‐50	  keV	  Δr = 100 nmΔh = 6.6 µm

3.4 µCourtesy of Anne Sakdinawat and Chieh Chang (SLAC)

Specialized	  x-­‐ray	  diﬀrac0ve	  op0cal	  elements	  enable	  new	  science	  at	  synchrotron	  facili0es	  Spiral zone plate for
producing x-rays withcharge 50 orbital
angular momentum

Uniformly redundant
array for x-ray parallel
holography, alignment,
and other applications

Zone plate for x-ray
differential
interference contrast
microscopy

Courtesy of Anne Sakdinawat and Chieh Chang (SLAC)

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 – δ + iβ
• 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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Total external reflection with finite β

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Normal incidence reflection at an interface

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Focusing with curved glancing incidence optics

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Fluorescent microprobe based in crossedcylinders

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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	f1: 25298m	mm	

PIN photodiode	mm	
f2: 15045m	

Undulator	

DCM	
TC1Slit	

Mirror manipulator	
Ion chamber	
Incident Slit	

SDD	Beam monitor	
Sample & Scanner	

Experimental hutch	

2006

Front end	

Courtesy of K. Yamauchi andH. Mimura, Osaka University.
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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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Multilayer mirrors satisfy the Bragg condition

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Multilayer mirrors satisfy the Bragg condition

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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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Atomic scattering factors for molybdenum (Z = 42)

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CXRO Web Site

X-Ray Interactions with Matter . Search CXRO

Facilities
Publications
ResearchX-Ray Tools
Visitors
Personnel
Comments?
Server Stats. About CXRO

www.cxro.LBL.gov/• 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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Sputtered deposition of a multilayer coating

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Multilayer coatings – “1D nanostructures”
World reference standard

Creating uniformity for
λ/50 optics

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

20Cr/Ti: 17%

Ti 2p

1510

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

ReflectanceWorld record inwater window
Reflectance (%)

Eric Gullikson, Farhad Salmassi,
Yanwei Liu, Andy Aquila (grad),Franklin Dollar (UG)

50445

450455460

Photon energy (eV)CheironSchool_Sept2013_Lec1.ppt

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Broad bandwidth mirrors
needed for as/fs pulses∆E(eV)	  ·∙∆τ(fs)	  ≥	  1.8	  fs·∙eV	  	  (FWHM)	  • 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.

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

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Photon energy, wavelength, power

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Lectures online at www.youtube.com

Amazon.com

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

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