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Fei Liu ([email protected]), Ferdi van de Wetering Muharrem Bayraktar, Fred Bijkerk (University of Twente)
Dries Smeets, Sjoerd Huang, Yongfeng Ni, Andrei Yakunin, Peter Havermans, René Oesterholt (ASML) Francesco Torretti, Joris Scheers, Oscar Versolato (ARCNL)
2019 EUVL workshop, Berkeley, USA, June 10th -13th
Lithography machine in-line broadband spectrum metrology
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Slide 2
Outline
• Source plasma emission spectrum measurement
• Emission spectrum impact on performance
• Proposed metrology and control scheme in the scanner
• Summary
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Slide 3
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EUV Source Key Physical Processes
Target Formation and Plasma Generation
𝑡0 𝑡0 + 𝛥𝑇
𝛥𝑥
COLLECTOR
IF
CO
2
La
se
r
CO
2
La
se
r
Droplet Travel →50kHz80m/s
PrePulse:Condition Droplet Into Target
MainPulse: Generate Plasma From Expanded Target
Courtesy of Matthew Graham
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Slide 4
EUV source plasma emission spectrum measurement setup
Tin droplets
y
z
x
Spectrometer, 90 to drive laser,77.5 to droplet
trajectory
Spectrometer [1]
(University of Twente)
Measurement range 5nm - 40nm; 130nm - 800nm
Technique Transmissive grating
Grating specs 10k lpmm; 3k lpmm; 1k lpmm;
0.5k lpmm
Detector specs PIXIS-XO 2048x512 imaging array
13.5x13.5 um pixels 27.6x6.9 mm
Calibration 10k lpmm and 1k lpmm gratings
calibrated at PTB
Advantages Broad wavelength range;
High resolution
[1] Muharrem Bayraktar ([email protected]), et.al. NEVAC Blad, 54, 14-19 (2016)
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Slide 5
Higher power source plasma characterized by higher
spectral purity
Definition Description
EUV IB 13.5±1% [nm] i.e 13.365-13.635 [nm]
EUV FB 13.2-13.8 [nm]
EUV OoB 5-70 [nm] excluding EUV FB
VUV 70-130 [nm]
DUV 130-400 [nm]
VIS 400-800 [nm]
IR >800 [nm] excluding 10260-10600 [nm]
CO2 10260-10600 [nm]
14+
15+
13+
14+ 12+
13+ 11+
12+
11+
10+ 9+
8+
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Slide 6
DUV spectra dependent on plasma recipesDUV lines are mainly from Sn1+, Sn2+, Sn3+
Definition Description
EUV IB 13.5±1% [nm] i.e 13.365-13.635 [nm]
EUV FB 13.2-13.8 [nm]
EUV OoB 5-70 [nm] excluding EUV FB
VUV 70-130 [nm]
DUV 130-400 [nm]
VIS 400-800 [nm]
IR >800 [nm] excluding 10260-10600 [nm]
CO2 10260-10600 [nm]
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Slide 7
DUV has an impact on system performance
Without pellicle:
• DUV reflection at Black Border (BB) on reticle over-exposes corners and edges → impact CD
With pellicle:
• Pellicle has higher DUV reflection than BB → more impact on CD
• DUV contributes to pellicle heating (40% absorption)
Field NField N-1
Reticle
Light reflected from BB in adjacent field
EUV exposure
EUV + DUV
DUV
BB
Wafer
DUV is ~0.3% of EUV measured in resist , within spec
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Slide 8
For future nodes, DUV suppression needs improvement
• Future nodes have tighter requirement on CD drop in corners:
improvement on DUV suppression is needed.
• HVM requires standardization of performance: minimum variation from
machine to machine, from time to time.
• Available options:
1. Spectral filters, which have an impact on EUV transmission
2. Optics coating improvement
3. Active feedback control for the broadband spectrum optimization
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Slide 9
DGL membrane as spectral filter to eliminate DUV impact [2]
• Suppresses DUV and IR, plus removes outgassing risk to POB
10 to 15% EUV transmission loss (due to membrane)
[2] Igor Fomenkov, EUV Source
Workshop, Dublin, Ireland (2017)
Effective DUV and IR suppression
>100x DUV suppression >4x IR suppression
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Slide 10
Possible solution: DUV anti-reflective coating [3]
Si3N4
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
12,8 13 13,2 13,4 13,6 13,8 14 14,2
wavelength (nm)
refl
ec
tiv
ity
standard capped ML
spectral purityenhanced ML
< 4.5 % EUV loss
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
100 120 140 160 180 200
Refl
ecta
nce
Wavelength (nm)
standard ML, exp. data
standard ML, simulations
AR coated ML, exp. data
AR coated ML, simulations
Effective suppression
for 100 < λ < 200 nm
[3] Eric Louis, et.al. SPIE 6151 (2006)
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Slide 11
Limitations of measuring spectrum at source for active
feedback control
• Measured perpendicular to
drive laser, since collector
covers a large solid angle
• Unknown DUV emission
angular dependency
• Collector impact not taken
into consideration
• Unknown clipping ratio at
intermediate focus
EUV
emitting
plasma
[4] Christian Wagner, et.al. Nat. Photonics, 4, 24-26 (2010)
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Slide 12
Proposed in-line broadband spectrum metrology in scanner
• Add extra band selecting mirrors to
field facet module, making use of the
light from far field, which is not used
for illumination.
• Under certain “non-lossless” pupil
configuration, it is possible to use
certain field facet mirrors which are
not used for illumination.
• Add sensors to pupil facet module, to
enable wavelength-dependent light
measurement.
No impact on EUV transmission
Intermediate FocusPupil Facet Module
Field Facet Module
Sensors consists
of optical filters
and photodiodes
Extra actuated
mirrors
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Slide 13
In-line broadband spectrum metrology and feedback
control system advantages
• Enables in-line broadband spectrum measurements
• Provides extra feedback loop signal for system broadband spectrum
optimization
• Proactively tracks the drift in the DUV and IR during production to avoid
pellicle overheating and imaging and overlay performance degradation
• Enables broadband spectrum optimization for pellicle, imaging and
overlay performance
• Enables quick trouble shooting when the scanner imaging and overlay
performance degrades
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Summary
• Source plasma emission spectrum is highly relevant for system
performance
• Using DGL membrane to eliminate DUV and IR at wafer level has an
impact on EUV transmission
• Using spectrum measured at source for feedback control has limitations
(unknown angular dependency, unknown clipping at IF, collector impact,
etc)
• It is advantageous to implement in-line broadband spectrum metrology
and control system in the scanner
Slide 14
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Acknowledgements
Igor Fomenkov, Alex Schafgans, Evan Davis, Daniel Brown,
Tim Goossens, Thomas Cummins, Olav Frijns, Roland Stolk,
Natalia Davydova, Harry Kreuwel, Wim van der Zande,
Eelco van Setten, Laurens de Winter, Dennis Zhang, Wouter Varenkamp,
Colm O’Gorman, Elena Nedanovska, Dries Munters, Jong-Koon Lim,
Ben Claas, Tijs Beenhakker, Martijn Geenen, Kees Feenstra,
Jeroen Rommers, Marc Haast, Jorge Quintana Ramirez,
Proto-21, Proto-7, EUV System Power Group
Slide 15
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