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22 August 2001 Silicon single atom steps as AFM height standards
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Atomic force microscopes (AFMs) are used in the semiconductor industry for a variety of metrology purposes. Step height measurements at the nanometer level and roughness measurements at sub-nanometer levels are often of interest. To perform accurate measurements, the scales of an AFM must be calibrated. We have been exploring the use of silicon single atomic steps as height standards for AFMs in the sub-nanometer regime. We have also designed and developed the calibrated AFM (C-AFM) to calibrate standards for other AFMs. Previously, we measured the step height of silicon single atomic steps on Si (111) (with native oxide) using the C-AFM. The value we obtained was 304 +/- 8 pm (k=2). From three independent measurement techniques, including our C-AFM result, we estimate an accepted value for the silicon step height of 312 pm +/- 12 pm (k=2), which corresponds to an expanded uncertainty of about 4 %. We have also completed a NIST led comparison of AFM measurements of silicon step samples to further evaluate their suitability as standards in industrial applications. If the reproducibility of the participants' measurements is sufficient, the accepted value could be used to calibrate the scale of the measuring tools in this sub-nanometer regime. The participants sent the data to NIST for analysis. This was done so that all of the data would be analyzed in a uniform manner. The results of our analysis indicate that these samples can be used effectively as standards. The average standard deviation of all of the participants results was 6 pm. Hence, it should be possible to use these specimens as sub-nanometer z-axis calibration standards with an expanded uncertainty of about 6 %.
© (2001) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Ronald G. Dixson, Ndubuisi George Orji, Joseph Fu, Vincent Tsai, Ellen D. Williams, Raghu Kacker, Theodore V. Vorburger, Hal L. Edwards, Debra Cook, Paul E. West, and Ralph Nyffenegger "Silicon single atom steps as AFM height standards", Proc. SPIE 4344, Metrology, Inspection, and Process Control for Microlithography XV, (22 August 2001);

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