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Fei Liu (fei.liu@asml.com), 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 (m.bayraktar@utwente.nl), 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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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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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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