multilayer-based solutions for suppression of ir radiation
TRANSCRIPT
DIFFER is part of and
Multilayer-based solutions for suppression of IR radiation in EUV systems
EUVL Symposium, Brussels, Belgium, October 2012
V.V. Medvedev1, A.E. Yakshin1, E. Louis1, R.W.E. van de Kruijs1, A.J.R. van den Boogaard1, F.A. van Goor2, V.M. Krivtsun3, A.M. Yakunin4, F. Bijkerk1,2
1 FOM Institute DIFFER, Nieuwegein, The Netherlands
2 MESA+ Institute for Nanotechnology, University of Twente, Enschede, The Netherlands
3 Institute for Spectroscopy RAS, Troitsk, Russia
4 ASML, Veldhoven, The Netherlands
2
Outline
o Parasitic IR radiation
o IR antireflective filtering + EUV reflection
o IR diffractive deflection + EUV reflection
o Summary
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Laser-produced plasma (LPP) EUV source
!!! A lot of scattered laser IR radiation
Mo/Si optics
Reflected CO2 laser radiation propagates
along with EUV
Heat loads on projection optics
Heat loads on wafer stage
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IR antireflecting multilayer mirrors
IR+EUV EUV
IR suppression + EUV reflection
Mo/Si multilayer is opaque for IR radiation
IR transparent materials should be used
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IR-transparent design
Philips Research Opt. Lett. 34, pg. 3680 (2009)
Full multilayer design:
Disadvantages:
o Complicated multilayer design
o Insufficient IR suppression (23x)
o Thick AR layers -> increased rougnhess
Rmin=4.4%
EUV
IR
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Classical quarter-wavelength antireflection
h = l/4nC
R1
R2
IR
R1=R2 requires perfect matching of refractive indices nC=(nS)1/2
Limited choice of materials for substrate
nC
nS
IR EUV
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Smart antireflective filtering
d1 nC
nS
metal d2
R1
R2
IR IR EUV
R2 = f(d2)
R1=R2 can be achieve by adjusting d2 for an arbitrary substrate
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EUV mirror + thin metal film AR coating
10 nm Mo layer
Si substrate
100xB4C/Si multilayer
Opt. Lett. 37, pg. 1169 (2012)
Magnetron deposited test coating
13.2 13.4 13.6 13.80.0
0.1
0.2
0.3
0.4
0.5
EU
V R
efl
ec
tan
ce
Wavelength, nm
6 8 10 12 140.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
IR R
efl
ec
tan
ce
Wavelength, m
45% EUV peak reflectance
IR suppression 250x
10
IR phase-shift suppression
p/2 p/2
RA
RB
zero order: R(0) = 0
l/4
Out-of-phase interference for specular reflection
Reflected radiation is distributed between off-specular diffraction orders
= 10.6 m – CO2 laser wavelength
h = l/4 = 2.65 m – groove depth
Calculated R(0) for square metal
grating h=l/4
2 4 6 8 10 12 1410
-3
10-2
10-1
100
0th-o
rde
r re
fle
ctio
n, R
(0)
p/l
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Test structures
50 m
Masked deposition of Si grating
Mo/Si multilayer deposition on top
of Si grating
Test structures:
p = 100 m
→ Diffraction angle at 10.6 m q ≈ 6°
H = 2.35 m ± 0.05 m (AFM measured)
→ Reflectance minimum at l ≈ 9.4 m
AFM profile
Opt. Lett. 37, 160 (2012)
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EUV Reflectance
61% EUV peak reflectance
Losses due to structure imperfections
Test IR-PsR structure, SEM top view
IR suppression 70x
5 10 15 200.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
IR R
efl
ec
tan
ce
Wavelength, m
13.0 13.2 13.4 13.6 13.8 14.00.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
EU
V R
efl
ec
tan
ce
Wavelength, nm
IR-PsR
Reference
10 m
13
Summary
Simple design of IR AR coating for B4C/Si based EUV multilayer
was proposed
test coatings were deposited using magnetron sputtering
250x IR suppression achieved
45% of EUV peak reflectance achieved
Design of grating-based IR SPF was proposed
test structures were manufactured using masked deposition
61% of EUV peak reflectance achieved
70x IR suppression achieved