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Lithography Optics Division
Optics forEUV Lithography
Martin Lowisch, Peter Kuerz, Thure Boehm,Hans-Juergen Mann, Stephan Muellender, Wolfgang Bollinger, Manfred Dahl, Michael Muehlbeyer, Siegfried Rennon, Frank Rohmund, Udo Dinger, Thomas Stein, and Winfried Kaiser
2007 EUVL Symposium
Lithography Optics Division
Page 2
The optical train – Introduction
Reticle-stage
Wafer stage
Source-Collector module
(SoCoMo)
Collector
Source
• λ 13.5 nm • NA 0.25• Field 26 x 33 mm2
• Magnification 4x
Design Example
Intermediate focus
illuminator
Projection optics
Lithography Optics Division
Page 3
overlay
throughput
CDUniformity
Coatingsreflectivity
Wavelength matching
Impact of optics on tool performance
ToolRequirements
Usable DoF
Exposurelatitude
Flare (MSFR)
aberrations
DesignNumber of mirrorsNumerical aperture
Illumination
mirrors are thekey components
DesignNumerical aperture
Illumination
Lithography Optics Division
Page 4
2D-isotropic PSD(example)
Lateral Frequency [μm-1]
figure
aberrations
CDU, overlay
Figure
MSFR
Optics Technology: Fabrication of EUV mirrors
HSFR
MSFR
in field of view scattering: flare
CDU
HSFR
reduced reflectivity
system throughput
Lithography Optics Division
Page 5
The “right” combination of fabrication technologies…
Computer ControlledPolishing for Deterministic Processes
Ion Beam Figuring:Atomic Level Figure Control
Fast Magneto Rheological Figuring
•The challenge for optics fabrication:Reduction of the Mid Spatial Frequency Roughness MSFR… and at the same time reduction of the figure ( aberration
control) and the HSFR (mirror reflectivity system transmission)
Lithography Optics Division
Page 6
… and improvements in mirror metrology
20 pm RMS Reproducibility
• statistical errors (repeatability):ES = 12 pm RMS surface figure !!!
• statistical errors + adjustment errors (reproducibility):EJ = 20 pm RMS surface figure !!!
12 pm RMS Repeatability
… enable very low figure values and reduced long wavelength MSFR contributions
New result on EUV mirrorFigure = 0.04 nm rmsMSFR = 0.13 nm rmsHSFR = 0.07 nm rms
Lithography Optics Division
Page 7
Optics Fabrication: Flare is determined by the Mid Spatial Frequency roughness
• Due to the small wavelength EUV is extremely sensitive to flare
2)(MSFR/λ⋅∝ mirrorsnFlare
Power spectral density (example)
MSFRFigure HSFR
Definition: All wavelengthsof the Power SpectralDensity which generate in-field scattering contribute to the MSFR
Lithography Optics Division
Page 8
flare reduces overlapof process windowsdue to dose offsets
proximity effects in dependence of thelocal reticletransmission
largest impact of flare on isolatedfeatures on bright-field masks
sensitivity of CD to dose errorsbecomes larger
Dose-to-targetchange
No flareWith flare
Main challenge: flare reduction
CD
Intensity cross-section
Lithography Optics Division
Page 9
Progress in flare reduction
Development focuses on material, polishing, and figuring
POB = Projection Optics Box
8% flare
Flare is calculated for a 2 µm line in a bright field
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
MS
FR [n
m rm
s](e
valu
ated
ove
r 4.6
dec
ades
)
test mirror
Set 3
Set 1
Set 2
test mirror(MSFR opt.)
MET2 mirrors
on-axis
AD-tool6 mirrorsoff-axis
setup POB mirrors
16% flare tools
New result on EUV mirrorsupports flare level < 8%Figure = 0.04 nm rmsMSFR = 0.13 nm rms
(0.06 nm rms in 3 decades)HSFR = 0.07 nm rms
2)(MSFR/λ⋅∝ mirrorsnFlare
Lithography Optics Division
Page 10
Coating Technology: EUV requires (almost) perfect nanolayers…
Challenges
Mo Si
substrate
θ
d
γ
EUV coatings:Mo/SiBragg reflectors
> 50 bilayers
high peakreflectance and large FWHM
wave-lengthmatching
> 70% shown < 0.2% shown
Lithography Optics Division
Page 11
Wave-length matching: transmission of a 10-mirror system
matchingTransmission
(integral)
± 0.0% 1.00± 0.1% 0.99± 0.2% 0.95± 0.3% 0.90± 0.4% 0.83± 0.5% 0.75
one mirror
10 mirrors
trans
mis
sion
Impact on a generic 10-mirrorsystem
Lithography Optics Division
Page 12
EUV Optics: The future
The next step:0.25 NA projection optics with sigma > 0.7 illumination systems (with
oblique illumination) enables: – 32 nm half pitch production– 22 nm half pitch R+D
Node ¥ NA 0.25 0.35 0.5
32 nm 0.59 0.83 1.19
22 nm 0.41 0.57 0.81
16 nm 0.30 0.41 0.59
11 nm 0.20 0.29 0.41
EUV is introduced as a high k1 technology
opportunity
NAkRES λ
1=
constant k1
k1 reduction
Lithography Optics Division
Page 13
Image log-slope is key parameter
How much contrast (image slope) do we have?
CDdxdI
INILS 1
=
dxdI
I CD
NILS is proportional to exposure latitude
CDCDNILS
EE Δ=
Δ2
Imag
e in
tens
ity
Lateral position
Aerial image cross section
Lithography Optics Division
Page 14
Dense lines 22 nm with conventional and annular illumination
0.2 0.3 0.40.3
0.4
0.5
0.6
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0
0.5
1
1.5
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0.2 0.3 0.40.3
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0.2 0.3 0.40.3
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0.2 0.3 0.40.3
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0
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1
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2
2.5
3best focus 50 nm defocus 100 nm defocus
Par
tial c
oher
ence
Annu
lar r
ing
radi
us
NA NA NA
NILS NILS NILS
Conventional illumination
Annular illumination
annular illumination enables R&D with NA=0.25
Lithography Optics Division
Page 15
30 nm and 22 nm dense contacts – conventional illumination
0.2 0.3 0.40.3
0.4
0.5
0.6
0.7
0.8
0
0.5
1
1.5
2
2.5
3
0.2 0.3 0.40.3
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0.2 0.3 0.40.3
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0
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2
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3
0.2 0.3 0.4
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0.4
0.5
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0.7
0.8
0
0.5
1
1.5
2
2.5
3
best focus 50 nm defocus 100 nm defocus
NA NA NA
Par
tial c
oher
ence
Par
tial c
oher
ence
30 nm contacts
22 nm contacts
Conventional illumination requires higher NA when shrinking contact pitch and CD
NILS NILS NILS
Lithography Optics Division
Page 16
dense contacts with conventional and quasar illumination
best focus 50 nm defocus 100 nm defocus
NA NA NA
Cen
ter r
adiu
s of
qua
sar
Par
tial c
oher
ence
0.2 0.3 0.4
0.3
0.4
0.5
0.6
0.7
0.8
0
0.5
1
1.5
2
2.5
3
0.2 0.3 0.40.3
0.4
0.5
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0
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1
1.5
2
2.5
3
0.2 0.3 0.4
0.3
0.4
0.5
0.6
0.7
0.8
0
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1
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2
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3
0.2 0.3 0.40.3
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0
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1
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1
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2
2.5
3NILS NILS NILS
30 nm contacts conventional illumination
22 nm contacts quasar illumination
Quasar illumination significantly enhances the process space at moderate NA with excellent image contrast
Lithography Optics Division
Page 17
And another step: Extendibility of EUV – design concepts
Design Examples
Possible production tool concept
for 22nm half pitch with
R&D extension towards 16 nm
US 6,710,917 B2
NA=0.25 NA>0.3 NA<0.5 NA>0.5
WO 2006/069725
Lithography Optics Division
Page 18
Summary
• key technologies are progressing towards production tool requirements– mirror figure– flare– coating technology (reflectivity, wavelength matching)
• Improved NA = 0.25 systems will address32 nm half pitch (production)22 nm half pitch (R+D)
• optical designs with NA > 0.3 support 22 nm half pitch production
• with designs for even higher NA´s (≥ 0.5) resolutions down to 16 nm and beyond arise at the horizon
Lithography Optics Division
Page 19
Thanks to a huge team effort at…
• FOM-Rijnhuizen• TNO TPD• PTB-BESSY• IWS Dresden• Philips• Heidenhain• The teams at ASML and Zeiss• …and many others
Part of this work was supported by:
Acknowledgment
German Federal Ministry of Education and Research projects 13N8088 and 13N8837, MEDEA+ projects "EXTATIC" and "EAGLE", European Commission project "More Moore" (IST-507754-IP).