RapidNano; an affordable particle detection
platform for EUV mask blanks
Peter Bussink, Jean-Baptiste Volatier, Peter van der Walle, Erik Fritz and Jacques C.J. van der Donck
TNO, P.O. Box 155, 2600 AD, Delft, The Netherlands
[email protected]
Introduction
Defect inspection for EUV masks is an area where
further development is required. According to the
ITRS roadmap1 defects smaller than 20 nm must be
detected (see Figure 1). Detection of this defects size
is not only challenging but also time consuming and
costly. For the qualification of EUV mask handling
equipment on particle cleanliness, TNO develops the
RapidNano, a tool that is capable of detecting nanoparticles on mask sized flat substrates.
Figure 1: Defect sizes for EUV masks (source: ITRS 2009/2013).
The RapidNano platform
Improvement strategy
In 2012 the smallest detectable particle was 59 nm.
To reach sizes which match the ITRS roadmap a
development program was started. First, a model for
the RapidNano was developed3. Based on this model
the performance of new configurations was
predicted and a path towards sub 20 nm particle
detection was found:
1. Speckle reduction for reduced background
variation
2. Decreased wavelength for increasing the amount
of scattered light from particles
RapidNano3
The threshold values for image processing was
mainly influenced by speckle. Using a 9-azimuth
illumination 9 independent speckle patterns were
combined4. A lower threshold could be applied.
The size of the smallest detectable particle depends
on the substrate roughness. For highly polished
silicon wafers particles of 42 nm can be detected
(PSL, 95 % capture efficiency) . For silicon terminated
MoSi blanks 45 nm particles can be detected (see
Figure 3) and for some CrN blanks a smallest
detectable particle size of 60 nm was observed.
CCD camera
•
•
•
MoSi blank (Si term.)
1 Watt laser power
50 milliseconds exposure time
Mean: 19
Max: 46
LDL: 45 nm LSE
Dark-field image.
Particle detection by setting
threshold in image processing
X, Y, Z-stage for stepping to next field
RapidNano4
The Rapid Nano 4 project is started in 2014
with the goal to build a follow-up on the RN3,
capable of detecting 20 nm particles. To
increase the sensitivity of the system, the
wavelength of the system is changed from 532
nm used in RN3 to 193 nm for the RN4. The
dark field detection method as well as the 9
illumination angles which were also
implemented in RN3 are maintained.
The substrates are placed in a protective TNO
designed scanbox to keep it clean during the
measurement. The scanbox with substrate is
loaded into the RN4 mini environment for
measurement. The mini-environment ensures
double protection against contamination.
In figure 4, the design of the RN4 is shown.
The expected performance of the RN4 is:
• Sensitivity: 20 nm particles
• Speed: 2 hours for a full mask inspection
• Connected to the TNO Reticle handler
system for automated handling of substrates
• Ultra clean measurement area.
Conclusion
Since 2002 generations of particle detection
equipment with increasing performance have
been developed.
The RapidNano3 is capable of detecting 42
nm particles on a full mask substrate.
The RapidNano4, for detecting sub 20 nm
particles is under construction.
Figure 2: Working principle of the RapidNano.
In 2011 the first stable and affordable detection
platform was achieved that was capable of inspecting
the full surface of a mask substrate2 (see Figure 2).
Literature
1.
2.
Figure 3: Background and histogram for MoSi blank.
3.
4.
2003
2004
2005
2006
2002: PS1
*100 nm
* 25 cm2 @ 0,15 cm2/min
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2012: RN1
* 59 nm (PSL)
* 225 cm2 @ 1.8 cm2 /min
* Level sensor
* Illumination
Sensor Head
Mini
Environment
RN2
Size > 50 nm (PSL)
405 nm
2011: PS4
* 70 nm (PSL)
* Full mask area
Filter Fan Unit
Pulse Stretcher
Generation skipped
2005: PS2
* 70 nm
* 70 cm2 @ 0,6 cm2 /min
Electronics
Rack
Metro Frame
Manual
Loading port
Source
Q4 2013: RN3
Size > 42 nm (PSL)
9 azimuth illumination
Figure 2: Development history and roadmap for the RapidNano particle scanner
Beam Delivery
Q2 2016: RN4
Size > 18 nm (PSL)
193 nm, illumination mode
3010 mm
2002
ITRS roadmap 2013
Donck, J.C.J. van der, Snel, R., Stortelder, J.K., Abutan, A., Oostrom, S., Reek, S.
van, Zwan, B. van der, Walle, P. van der, “Particle detection on flat surfaces”,
Proc. SPIE 7969, 1S (2011).
Walle, P. van der, Kumar, P., Ityaksov, D., Versluis, R., Maas, D.J., Kievit, O.,
Janssen, J., Donck, J.C.J. van der, “Nanoparticle detection limits of TNO’s Rapid
Nano: modeling and experimental results”, Proc. SPIE 8522, 2Q (2012).
Walle, P. van der, Kumar, P., Ityaksov, D., Versluis, R., Maas, D.J., Kievit, O.,
Janssen, J., Donck, J.C.J. van der, “Increased particle detection sensitivity by
reduction of background scatter variance”, Proc. SPIE 8681, 16 (2013).
Electronics
Rack
Load Port for
Reticle Handler
X,Y,Z,qx,qy Stage
Main Frame
Figure 4: Design of RapidNano 4.
This work has been performed in the framework of the
International Center for Contamination Control, established
by TNO. Partners are welcome to join ICCC in the challenging
development of dedicated contamination control solutions.