Improved AFM Tip Calibration Reduces Uncertainties on SRM 2059 Master Standard
One of the most venerable of MEL Standard Reference Materials is SRM2059 – the latest installment in a series of photomask linewidth standards that traces its history back to the 1970s when the first NIST Standard Reference Material (SRM) for photomask metrology (i.e., SRM474) was introduced. At the annual SPIE Photomask Technology conference (also known as BACUS), MEL researcher Ronald Dixson presented the results of recently improved critical dimension atomic force microscope (CD-AFM) measurements on the SRM 2059 control sample.
The SRM 2059 control sample also serves as a master standard in the SRM calibration paradigm. Due to uncertainties in the optical modeling, the current release was calibrated by using CD-AFM to measure the feature widths on the control sample. The NIST ultra-violet (UV) microscope was then used as a comparator by MEL scientist Jim Potzick – the SRM 2059 project leader – to calibrate the remaining standards for sale to NIST's customers.
The original AFM measurements were performed by Dixson in 2004 – during his tenure as a NIST Guest Scientist at SEMATECH - a consortium made up of members of the world's leading semiconductor industries. These original measurements had expanded uncertainties of at least 10 nm (k = 2) – due to the uncertainty in the AFM tip calibration. The AFM uncertainties ultimately comprised a significant component of the final combined uncertainties on the masks for sale.
Subsequent to those original measurements, the NIST single crystal critical dimension reference material (SCCDRM) project was completed. This work, which was a collaboration between EEEL, MEL, and ITL, enabled tip widths to be calibrated to 1.5 nm (k = 2), and provided an opportunity to reduce the uncertainties on the control sample.
The new measurements performed by Dixson had combined expanded uncertainties of 2 nm to 3 nm (k = 1) for the sub-micrometer features – which represents between a factor of three and four improvement over the prior measurements. When the reanalysis of the optical comparator data is completed by Potzick, this should lead to at least a 40 % improvement in the final uncertainties reported to customers.
Contacts: ron.dixson [at] nist.gov (Ronald Dixson), 301 975 4399 and potzick [at] nist.gov (James Potzick), 301 975 3481
MEL Provides Input to Secure Large Electric Systems
In November 2008, MEL researcher Keith Stouffer traveled to Lisbon, Portugal to present at and participate in the CIGRE B5.38 4th Standards Meeting. CIGRE (Conseil International des Grands Reseaux Electriques) - the International Council on Large Electric Systems is one of the leading worldwide organizations on Electric Power Systems, covering their technical, economic, environmental, organizational and regulatory aspects. CIGRE commissioned the B5.38 committee to perform a study to survey the threats and attack scenarios applicable to protection and automation systems, and to survey existing recommendations that offer operationally efficient and cost effective cyber security solutions, including the International Electrotechnical Commission (IEC) 61850 standard for the design of substation automation.
IEC 61850 is an open system standard that is gathering significant world-wide momentum to become the dominant basis of protection and automation systems not only within substations, but between substations, between substations and control centers, and between substations and other remote locations. One feature of IEC 61850 is its strong emphasis on interoperability between intelligent electronic devices (IEDs) manufactured by different vendors. Another strong feature is the open publication of the IED data dictionary and communication services supported for most protection and automation functions. Lastly, IEC 61850 includes the specifications for peer-to-peer operation over high-speed communication channels using the Internet Protocol (IP).
During this meeting, the B5.38 committee worked on finalizing the technical brochure on the impact of implementing cyber security requirements using IEC 61850 recommended by various study groups and standards organizations including the work that NIST and ISA99 have performed in this area. The committee also developed a draft article to be published in CIGRE's ELECTRA magazine summarizing the findings specified in the technical brochure.
Contact: keith.stouffer [at] nist.gov (Keith Stouffer), 301 975 3877
NIST Organizes Major Response Robotics Exercise
A NIST organized rescue robot exercise in Texas gathers 130 participants. Three dozen robots were put through their paces by developers and first responders in the November 2008 exercise. This exercise was sponsored by the Department of Homeland Security's Science and Technology Directorate to develop performance standards for robots for use in urban search and rescue (US&R) missions. The exercise is an important step in helping prepare performance standards that are being hosted by ASTM International under their E54 Homeland Security Applications Committee.
The event took place at Disaster City, Texas, a test facility run by the Texas Engineering Extension Service (TEEX), a part of the Texas A&M University System. The facility offers an airstrip, a lake, two train wrecks, three rubble piles, a variety of collapsed buildings, and other unique disaster "props" that can be arranged for many types of challenging tests. The robots were run through realistic training scenarios, as well as through nineteen test methods that have either been already approved or are being prepared for balloting within ASTM. This exercise provides the end users and manufacturers the opportunity to develop concepts of operation for deploying robots in a variety of response missions and to comment on the developing test methods.
Test methods included measuring battery capacity by having robots perform figure eights on an undulating terrain and mobility tests in which robots ran through increasingly challenging exercises such as maneuvering on stairs, ramps, confined spaces, and gaps. Several aquatic test methods, such as visual acuity, were tried out by underwater robots. A critical performance parameter that has a strong influence on overall system capability is the communication link between the user and the robot. Proposed test methods were studied for evaluating the performance of wireless links used on US&R robots under both line-of-sight and non-line-of sight conditions. Data gathered during the exercise will help researchers to revise the proposed test methods. A new mapping challenge introduced at this event evaluated the accuracy of the robot-generated map. Researchers came from across the globe to collect data to feed into their mapping algorithms.
NIST was well-represented, with participants from MEL leading the effort, BFRL providing high-resolution ground truth capture using 3D sensors, and EEEL directing the wireless communications test methods mentioned above.
Contact: adam.jacoff [at] nist.gov (Adam Jacoff), 301-975-4235, Galen Koepke, 303-497-5766, %20alan.lytle [at] nist.gov (Alan Lytle) 301-975-6048
Multi-Model SEM Simulations Completed
In the semiconductor manufacturing industry, routine linewidths for process monitoring are measured using critical dimension - scanning electron microscope (CD-SEMs). Monte Carlo simulations of the beam-specimen interactions determine the instrument response profile from various line-edge shapes. To quickly determine the line-edge shape from the image intensity profile—a library of images is modeled that can be quickly scanned and interpolated for the best match. Models with fitting parameters are usually "tuned" to match measured yields on flat samples. MEL researchers completed the first phase of a multi-model SEM simulation study. A large number of simulations of SEM line scans across trapezoidal line edges have been completed. Each simulated line scan represented 10000 electron trajectories at each of 101 landing positions. Line scans were calculated for each of nine sidewall angles in two materials (Cu and Si) at four incident energies and 10 different models or model variants. The main model families were a binary collision model based upon Moller scattering (this was the NIST-developed MONSEL's original model – a Monte Carlo based simulation model), a many-body model based upon dielectric function theory, and a phenomenological fit-based model that used the ideas of David Joy, a well known SEM researcher. Within each of these families there were variants depending upon assumptions about barrier scattering or other model-specific assumptions. The simulations, which required approximately four months of CPU time (on 3.4 Ghz PC-based processors), form the data set for a study of the sensitivity of model-based dimensional measurements to model assumptions. Initial results from these simulations indicate there are nevertheless significant secondary electron yield differences between models in the important edge region of the image. The effect of these yield differences on dimensional measurements depends upon sensitivity coefficients. The next phase of this study will determine the sensitivity coefficients.
Contact: %20jvillar [at] nist.gov (John Villarrubia,) 301 975 3958
First Quarterly review held for the Atomically Precise Manufacturing Consortium
MEL's Atom-based Dimensional Metrology project was awarded a 5-year, 3-phase Defense Advanced Research Projects Agency (DARPA) contract to conduct collaborative research in atomically precise positioning, patterning and metrology. A two day review and workshop was held in Dallas TX with all members of the Tip Based Nanofabrication Program funded by DARPA. The primary collaborators in the Zyvex led Atomically Precise Manufacturing (APM) program, include NIST, The University of Illinois, The University of Texas at Dallas (UTD), The University of Texas at Austin, Zyvex labs and others on scanning tunneling microscopy (STM) tip development and characterization. In the first quarterly review MEL's Rick Silver and Jason Gorman presented updates on the MEL-led components of the project: atomic scale tip characterization, atomically precise silicon sample preparation, and lithography and metrology on the atomically resolved surfaces. MEL's research will include characterization of tip structures and STM operational characteristics on atomic lattices. MEL will also participate in Micro-Electro-Mechanical Systems (MEMS) scanning element design for large arrays of actuated tips as well as help characterize the 3D passivation process to be developed at UTD. The long term goal of this program is to develop economically viable manufacturing solutions at the nanometer scale that involve atomically precise patterning and metrology using an array of independently functional tips. This is a very exciting project as it addresses future, very advanced manufacturing challenges that will be encountered in extending nanomanufacturing to the atomic domain with manufacturing capable solutions.
Contact: richard.silver [at] nist.gov (Rick Silver), 301 975 5609
NIST/MEL Associate, Eswaran Subrahmanian Elected AAAS Fellow
Dr. Eswaran Subrahmanian, guest researcher in the Manufacturing Engineering Laboratory was elected to be a Fellow of the American Association for the Advancement of Science (AAAS). Dr. Subrahmanian is being recognized for his distinguished contribution to design theory and methodology and its implications for design support systems and for bridging theory, practice and education in engineering design. The award will be presented February 14, 2009, in Chicago.
Contact: sriram [at] nist.gov (Ram Sriram), 301 975 3507