EUV and Soft X-Ray Optics
David Attwood
University of California, Berkeley
andAdvanced Light Source, LBNL
Cheiron School
October 2010
SPring-8
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The short wavelength region of theelectromagnetic spectrum

n = 1 – δ + iβ

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

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Refractive index from the
IR to x-ray spectral region

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Refractive index at nanometer wavelengths

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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_Oct2010_Lec1.ppt

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Diffraction from a transmission grating

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A Fresnel zone plate lensCheironSchool_Oct2010_Lec1.ppt

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

CheironSchool_Oct2010_Lec1.ppt

10Depth of focus and spectral bandwidth

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Zone plate diffractive focusing
for higher orders

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A Fresnel zone plate lensfor soft x-ray microscopy

Courtesy 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

Outerzone
close-upOuter zones

Inner zones

E. Anderson, LBNL
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CheironSchool_Oct2010_Lec1.ppt

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 andresolution 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 of
periodicity 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=NAcond
NAobj(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)(2000 X 2000, CheironSchool_Oct2010_Lec1.ppt
104 ph/pixel)

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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 atNSRRC, Taiwan

400 nm2

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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5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 pressureusing multilayer coated focusing opticsCheironSchool_Oct2010_Lec1.ppt

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X-ray microprobe at SPring-8
Optical microscope
PIN photodiodemm

f1: 252mm

f2: 15098m
45m

SDDMirror manipulator

DCMUndulator

TC1SlitIon chamber

Beam monitor
Sample & Scanner

Incident Slit
Experimental hutch

2006

Front end

Courtesy of K. Yamauchi and
H. 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 amultilayer 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
PersonnelComments?
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

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Cr/Ti: 17%Ti 2p

1510CX050622B
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

450

455460

Photon energy (eV)CheironSchool_Oct2010_Lec1.ppt

Recent progress in multilayer mirrors
Near-Normal Incidence Multilayer Mirrors80Sc CTiVPeak reflectance (%)

7060

SiH 2Owindow50403020Au100110
Wavelength (nm)CheironSchool_Oct2010_Lec1.ppt

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Multilayer Laue Lens for focusing hard x-rays

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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 layersN<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.

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

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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/sxr2009CheironSchool_Oct2010_Lec1.ppt

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