January/February 2010

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January/February 2010
CLEANROOM NEWS
PROCESS NOTES: 2-D Stylus Profilometry for Film Thickness Measurement
LCI NEWS
TECHNOLOGY TRANSFER
FACULTY PROFILE
CLEANROOM NEWS
The cleanroom staff has spent a considerable amount of time in recent months developing
training materials for liquid crystal device prototyping. Cleanroom assistants Bill Eckert, Matt
Wayman, and Pat Toothaker have completed a basic set of videos to train users on the most
commonly used equipment in the LCI cleanroom. They will continue work this semester to add
additional videos for advanced/specialty equipment and for basic cleanroom procedures.
Modifications to the MRC 603III Sputter Coater continue. The pulse DC module has been
installed, and test depositions have been completed. The ITO target will be installed next, with
process development to follow. Some system upgrades, including replacement of gas lines,
addition of 2nd gas mixture, and cooling water pump/filtration should also be completed in the
next month.
The new substrate platen for the Asymtek A403 XY Dispenser is being resurfaced due to issues
with flatness introduced during the machining process. The reworked platen should be installed
and leveled by the end of February. The camera illumination will be upgraded so that users can
easily view fiducial markings in ITO. Camera mods should be completed concurrently with the
platen upgrade.
The Tencor Alpha Step 200 Profilometer was recently serviced to correct a problem with stage
up and down motion.
If there are particular pieces of equipment that are of interest to you, or if you would like to see
particular capabilities added to the room, please contact Doug Bryant.
PROCESS NEWS: 2-D Stylus Profilometry for Film Thickness Measurement
To successfully fabricate most liquid crystal devices, it is necessary to coat substrates with thin
films measured in thicknesses of microns or less. Film uniformity and reproducibility is critical
to successful photolithography, and alignment layer thicknesses must be controlled as well. Thus
it is critical to have a good metrology tool for film thickness measurement. Two common
methods for film thickness measurement are ellipsometry and profilometry. In this article, we
will give a brief overview of two dimensional surface profilometry, and compare two different
methods used by commercially available profilometers (a more detailed discussion can be found
in reference 1).
To measure film thicknesses via profilometry, a clean step feature is necessary. This can be an
edge patterned by photolithography, or created with a razor blade (note this may require
destructive testing). Solvent based methods do not generally work well, as the edge is not sharp
enough to give an accurate measurement.
In stylus profilometry, a fine diamond tip (the stylus), mounted at the end of a beam or “arm”, is
translated a short distance across a substrate, and the resulting up and down motion of the stylus
is recorded. The linear voltage differential transformer (LVDT) sensors are sensitive enough to
detect motions of the stylus of less than a nanometer. Profilometers usually do linear scans of
less than 100 microns and up to tens of millimeters. Downward force can be controlled to allow
measurement of softer films.
In some commercial profilometers, a pivot point is defined and fixed relative to the measurement
head (Figure 1). The stylus, free to move up and down, is then moved (parallel to the stylus arm)
or scanned across a test substrate. The table surface is generally machined flat, and aligned
parallel to the plane of motion of the stylus. This is the design approach used in the Sloan Dektak
surface profilers.
Figure 1. Surface profiler stylus arm design (from ref 6)
The second common design approach is sometimes called a pivoting step measurer, since the
stylus arm pivots around a fixed post (see Figure 2). Tencor Alpha Step profilometers employ a
variation of this approach, and are still very popular even several decades after their introduction.
Pivoting step measurers are simpler to design, as the motion is easily controlled by the fixed pivot
point and a drive wire.
(Figures 2 and 3 from Ballinger, ref 1)
One issue with pivoting step measurers is linearity of the scan. Because the stylus rotates about
the pivot point, the scan actually traces an arc (see Figure 3 above). For very short scans, this
does not cause a problem, but longer scans will have a noticeable arc. The main problem caused
by this is not usually the path deviation of the stylus (the offset from linear is small), but is the
change in height caused by small tilts of the substrate with respect to the stylus motion. Figures 4
and 5 below show how a very small deviation from planar (0.11 degrees) causes a noticeable
curvature to the scan.
(Figures 4 and 5 from Ballinger, ref 1)
Because of this issue, pivoting step measurer type devices are not used as often for surface
roughness measurements or large area surface profiling. They are quite acceptable for step height
measurement (film thickness), which usually requires very short scan distances (<500 microns).
True surface profilers can be used over long distances (>10mm) with excellent accuracy.
The size of the stylus tip can also impact surface profile measurements. Figure 6 shows how
different diameter tips can impact the resulting profile. Standard tips range from 12.5 micron
diameter down to 1 micron diameter. Larger tip sizes cannot accurately measure channels on the
order of the tip diameter. This is not usually a problem for simple step height measurements,
however.
Figure 6. Effect of stylus tip diameter on scan accuracy (from ref 2). Left shows effect of
different stylus shapes. Right shows actual geometries for Tencor Alpha Step 200.
The LCI cleanroom uses a Tencor Alpha Step 200 profiler for film thickness measurements (a
pivoting step measurer). Thin film thicknesses of ~100 angstroms up to 5 microns can be
measured successfully. If you are interested in more information about this tool, or to reserve
time on it, please contact Doug Bryant.
References
1. Ballinger et al, “Geometric Considerations of Surface Profilers and Pivoting Step
Measurers,” Veeco technical document c2004. (available for download at reference 4
below).
2. Tencor Alpha Step 200 users manual (hard copy at LCI).
3. http://www.veeco.com/library/Application_Notes.aspx?ShowOpt=0&ID=73
4. J. M. Bennett and J. H. Dancy, "Stylus Profiling Instrument for Measuring Statistical
Properties of Smooth Optical Surfaces," Appl. Opt. 20, 1785-1802 (1981).
5. http://en.wikipedia.org/wiki/Profilometry
6. http://www.stinstruments.com/Stylus%20profilometer1.htm
7. Fruhauf, J, “Problems of contour measuring on microstructures using a surface profiler”,
Meas. Sci. Technol. 9 (1998) 293–296.
8. Song, J.F. and Vorburger, V.T., “Stylus profiling at high resolution and low force,” Appl.
Opt. Vol. 30, No. 1 / 1 January 1991
LCI NEWS
Recent Seminars
January 20, Dr. Craig Maloney, Carnegie Mellon University, "Plasticity and Jamming"
January 29, Dr. Surajit Dhara, School of Physics, University of Hyderabad, "Perfluoropolymer
as an Alignment Layer Liquid Crystals"
February 3, Dr. Paul Russo, Department of Chemistry, Louisiana State University, "Learning
from Polypeptides"
February 10, Dr. Yuka Tabe, Waseda University, "Dynamical Cross Coupling in Chiral Liquid
Crystals
Upcoming Seminars
February 17, Dr. Georg Fantner, Massachusetts Institute of Technology, Title: T.B.A.
March 3, Mark Taylor, Hiram College, Title: T.B.A.
March 10, James Watkins, University of Massachusetts, Title: T.B.A.
March 24, Rudolf Oldenbourg, Marine Biological Laboratory, Title: T.B.A.
April 7, Linda Hurst, University of California, Merced, Title: T.B.A.
April 21, Bob Austin, Princeton, Title: T.B.A.
April 28, Juan de Pablo, University of Wisconsin, Title: T.B.A.
May 5, Stuart Rowan, Case Western Reserve University, "Utilizing Supramolecular Chemistry
to Access Stimuli-Responsive Materials" Note: This is a joint colloquium with the Department of
Chemistry
Hiroshi Yokoyama joins the Liquid Crystal Institute as Ohio Research Scholar
As part of the Ohio Department of Development’s Ohio Research Scholars Program, the Liquid
Crystal Institute recently recruited Professor Hiroshi Yokoyama to be an Ohio Research Scholar
and Professor in the Chemical Physics Interdisciplinary Program at Kent State University.
Professor Yokoyama is a world expert in the field of liquid crystal physics with a focus on
surface properties. His primary research interests are in the areas of liquid crystals, surface and
colloid science, organic thin films and scanning probe technology.
In addition to his well-known research on surface anchoring and orientational boundary transition
in liquid crystal systems, he organized and directed, from 1999-2004, the "Yokoyama
Nanostructured Liquid Crystal Project" under the ERATO system funded by Japan Science and
Technology. This project pioneered the now flourishing soft matter nanotechnology which is one
of the major pillars of the Ohio Third Frontier Program.
His research efforts at the LCI will be associated with the recently funded grant, "Research
Cluster on Surfaces in Advanced Materials (RC-SAM)". RC-SAM is a partnership of Kent State
University, Case Western Reserve University, Youngstown State University, Alpha Micron, Inc.,
Cleveland Botanical Garden, CoAdna Photonics, Inc., Kent Displays, Inc., Kent Optronics, Inc.,
and LXD, Inc. He will be leading a partner-wide initiative to explore the new frontier of liquid
crystal applications by combining nanotechnology with liquid crystal science. Professor
Yokoyama's activity will also embrace the establishment of an international research and higher
education network centered on soft matter nanotechnology.
Professor Yokoyama most recently held the position of Director of the Nanotechnology Research
Institute (NRI), National Institute of Advanced Industrial Science and Technology (AIST), one of
the largest government-funded research organizations in Japan, which is responsible for strategic
planning and implementation of research programs over the whole spectrum of nanotechnology.
TECHNOLOGY TRANSFER
KSU.325 – BROAD RANGE NANO-LITER VISCOMETER
Kent State University Inventors:
Dr. Antal Jakli (faculty) and Dr. Christopher Bailey (doctoral student)
This Kent State University technology for a broad-range nano-liter viscometer is particularly
useful in rheological studies of expensive and/or commercially-unavailable complex fluid
materials. These could include novel liquid crystals, bent-core materials, elastomers, liquid
crystals with nanoparticles, etc. It is also applicable and highly useful with soft matters with
biological relevance, such as DNA solutions.
Most traditional rheological equipment (working by capillary, rotational, falling/rolling ball
techniques, etc.) require amounts of material on the order of a mL. Various micro-fabrication
techniques using microchannels, that can bring material volumes down to about 20 nL, also are
recognized to have limited usage as a general rheological tool. This simple KSU.325 device
works without the need of microchannel technique, requires use of only typically 10 nL of
material, and works in a wide viscoelastic regime, allowing optical observations and temperature
regulation.
Among its advantages are that it is simple and relatively inexpensive; and it allows study of
complex materials together with their optical properties.
This technology is available for licensing, with patent application in process.
Please contact us below if you wish to discuss a license for this or any other Kent State
technologies:
From the Office of Technology Transfer and Economic Development, Kent State University
www.techtrans.kent.edu (Please visit the “For Industry” section)
Licensing Information Contacts:
Gregory B. Wilson, Associate Vice President,
Charmaine Streharsky, Ed.D.
Economic Development and Strategic Partnerships
Licensing Coordinator for Technology
[email protected] 330-672-3553
Transfer [email protected] 330-672-0704
FACULTY PROFILE
Hiroshi Yokoyama
Ohio Research Scholar and Professor, Chemical Physics
Tel.: (330) 672 2633
[email protected]
Nano-Engineering the Liquid Crystal Surface Alignment
Tailoring the initial orientation of liquid crystal by the action of cell surfaces is a crucial step in
fabricating most, if not all, of current high-performance liquid crystal devices (LCDs). The
underlying phenomenon, known as the surface-induced alignment, is the subject matter Hiroshi
Yokoyama has been studying for 30 years in Japan.
His recent interest lies in adding more active functionalities to surface-induced alignment by
means of “nano-engineering” of alignment surfaces. A typical example of his approach is to
fabricate microscopic patterns of liquid crystal orientation so that the resulting elastic conflict,
inducing higher energy states, gives rise to multiply stable alignment. The multi-stability is the
basis of memory capability, which is of big advantage for low-energy consumption e-book
applications of LCDs. More generally, the art of micropatterning allows a wide range of
reconfigurable surface alignment of liquid crystals, which should be useful not only for displays
but also liquid-crystal based devices such as fiber optic switches and optical sensors.
The fabrication technique evolved from atomic force microscope (AFM) nanorubbing, just for the
initial proof-of-concept, to the photo-alignment and the nano-imprint patterning technologies,
both of which are strong candidate for industrial implementation of the micro-patterned
alignment. He has been involved in development of photo-alignment materials and novel
exposure techniques that help its application to micropatterning possible. The nano-imprint is an
emerging microfabrication technology that can be versatile and can process large area by simple
stamp-and-step procedure. At the LCI, he is in search for industrial partners toward real
industrial applications of this technology, and is also advancing the micropatterning concept to
newer electro-optical functionalities
Tri-stable surface alignment on a hexagonal
orientational micropattern generated by the AFM
nanorubbing technique.
J. Kim, M. Yoneya and H. Yokoyama, Nature 420,
159(2002).
4cm X 4cm bistable LCD using a checkerboard orientational micropattern fabricated by the
mask-exposure photo-alignment.
J. Niitsuma, M. Yoneya and H. Yokoyama, Appl. Phys. Lett. 92, 241120(2008).
J. Niitsuma, M. Yoneya and H. Yokoyama, Jpn. J. Appl. Phys. 48, 040201(2009).
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