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).