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Concept Studies for Actinic Pellicle Characterization
Metrology in an Industrial Environment R. Lebert, C. Pampfer, C. Phiesel, A. Biermanns-Foeth, T. Mißalla, C. Piel
RI Research Instruments GmbH, D-51429 Bergisch Gladbach
RI Research Instruments GmbH Phone: +49 2204 7062 2500 Friedrich-Ebert-Strasse 75 Fax: +49 2204 7062 2501 51429 Bergisch Gladbach web: www. research-instruments.de Germany
Contact: Dr. Rainer Lebert Phone: +49 2204 7062 1216 Fax: +49 2204 7062 2501 email: [email protected]
2016 International Symposium on EUV Lithography
Introduction
The scene is set for volume chip production with EUV lithography in 2018. However, EUV masks with pellicles are considered a corner stone for insertion. Making them ready in time imposes challenges also on actinic metrology tools. Hence, solutions feasible for the industrial environment (throughput, cleanliness, accuracy) are required within a very short time scale.
Within RI Research Instrument’s approach of supporting
EUV mask infrastructure with actinic metrology, we have
studied the demands on EUV pellicle characterization
coming from the supply chain. Based on our experience on
characterization of resists and masks and on our
established EUV metrology sources, we have studied
various solutions for this tasks and benchmarked them
with respect to industry’s needs.
EUV- Pellicles
EUV pellicles are envisioned as feasible solution to reduce
the impact of particle contamination on the front side of
reticles. The pellicle is a thin film (≈ 50 nm) placed
approximately 2 mm away from the patterned surface of a
reticle. Particles that would have otherwise landed on the
patterned side of a reticle will now land on the pellicle.
Because these particles are now out of focus their impact
on the imaged pattern is strongly reduced.
Core quality and design features
• Reliable, clean stand-alone laboratory EUV Source with
sufficient power , long and short time stability
• Source pulse synchronized fast shutter
• Effective EUV inband filtering
• Precise dose monitoring
• Clean process environment (in- and ex-vacuum)
• Sample stage and transfer design optimized to minimize
probability for any contamination reaching the pellicle
Proof of concept experiment
As a first proof of concept experiment, we have measured the EUV transmission of a 200 nm thick Zirconium window with support mesh in a rudimentary process just taking two images and dividing them pixel by pixel. Inhomogeneous illumination has been intentionally accepted and was of little relevance for the result.
Metrology concept study
Various optical concepts have been studied for solving the task:
The “inband filtered beam” with CCD registration has
been selected for speed and quality and because it
provides additional information easily as referencing to the
borders and detection of defects.
Acknowledgments: Thanks to the BMBF and the EU-ECSEL for funding within
the project 16ESE0048 “Autonome aktinische EUV Masken Metrologie”
and in SeNaTe (ESECS 14203).
Thanks to the team from IBS Precision Engineering BV for fruitful cooperation.
Transmission measurement of full area EUV pellicles
at 13.5 nm wavelength
• Optical layout
• Metrology concept
Measurement
accuracy
• Design means
• Component/material selection
• Cleaning and assembly
Defectivity and
cleanliness
• Proven and available
technologies Timeline
Key c
halle
ng
es
EUV-Lamp
Debris MitigationMultilayer filter unit
CCD-Camera
Shutter
Inband FilteredMonitors (E-MON)
XYZ stages
Load-Lock
Pellicle transfer
Gate Valves
Pellicle
Process chamber
System control and evaluation
SPF and irradiation monitor
Signal registration
Vacuum and gas flow
Measurement accuracy
Defectivity & cleanliness
Lid
10
Functional Schematic of EUV Pellicle Transmission Tool (green: important for cleanliness; purple: important for accuracy)
Reference “I0” Image
Measurement Image
Spatial resolved Arial result of transmission
with CCD behind SPF and ML-Filter Unit
Proof of concept experiment for evaluation: Homogeneity of irradiation is desired but not required
Multilayer + Zirconium + Argon is effective EUV inband filter
Target specifications
Mechanical design of production environment compatible EUV Pellicle Transmission Tool
Task and key challenges
We have investigated in how far our existing components,
concepts and solutions could be matched to the task of
actinic EUV pellicle transmission metrology and came up
with a tool design.
Concept Pro Con
Monochromator spectral + diode
Full information
Very slow
Monochromator 13.5 nm integral + diode
Faster Not “inband”
Polychromatic spectroscopic + CCD
Much faster Slow for full area as many images
“Inband” filter + CCD Fast + defect information
Image evaluation software required
Inband Filtered Beam from EUV-Lamp
Inband Filtered Beam from EUV-Lamp is generated by:
• Use EUV-Lamp’s broadband Xenon emission spectrum
• Filter to 13.5 nm with two multilayer mirror reflection
• Suppress UV, VIS & IR by Zirconium film + Argon purging
Mechanical design of the EUV pellicle transmission tool
• Compact design
• Cleanroom compatible
• Pellicle loading in local ISO-1 environment
Feature Target spec Rationale
EUV transmission range 0.1…100 % CCD dynamics
Accuracy (T=80…100 %) < 0.05 % Self-calibrated
Precision < 0.1 % (3σ) Dose monitor
Mapped area Full pellicle Design
Position accuracy 20 µm Self-referencing
Measurement time < 1 hour Concept &
source
Cleanliness (> 5 µm added
particles per cycle) < 0.01 Design
Availability 95 % Experience
Environment ISO 5 Design
Making pellicles usable in EUV scanners, they must
undergo several qualifications for supplying reproducible
quality to the industry. One core feature is the uniformity
of the transmission at 13.5 nm through the pellicle
membrane over the entire surface. The specification for
the required tool is qualifying an average EUV transmission
of > 88% to a uniformity of > 99.6 % – hence precision and
accuracy of the process of below 0.1 % are demanded.
Schematic of EUV Pellicle and its function R. Peeters, ASML, SPIE 2014, San Jose
