29 March 2012 Traceable pitch metrology: supporting the development of patterned media and more
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Abstract
The data storage industry seeks data densities of several terabits per square inch, corresponding to dot pitch <15  nm. Cost constraints prohibit using commercial microscopes designed for accurate measurements. However, we show it is possible to routinely make accurate pitch measurements with commercial general purpose atomic force microscopes and scanning electron microscopes by using a calibrated grating as a transfer standard. This provides short-term traceable calibration. Our accuracy was validated in two collaborative projects with three national metrology institutes. In the first project, we measured the pitch of a 144-nm two-dimensional grating. Our mean value agreed within 0.033 nm with that obtained at the PTB (Germany) optical diffraction lab. In the second project, described in detail here, we measured the pitch of a 70-nm one-dimensional grating. Because we used two measurement runs, the statistical treatment is more elaborate. We use basic statistical methods, such as analysis of variance, correlation, and tests of statistical significance, to draw key conclusions and enable us to combine the results of both runs to get an improved mean pitch value with some reduction in uncertainty. Our mean value agreed within 0.025 nm of the values found using the calibrated AFMs at National Institutes of Standard and Technology (NIST, USA) and National Metrology Centre (NMC, Singapore); furthermore, our uncertainty matched that of the other labs. The relative standard deviation (SD/mean) of individual pitch measurements is a figure of merit for the measurement system consisting of grating plus microscope.If the relative SD can be held below 0.5%, we have a clear roadmap to provide useful traceability for pitch standards down to 5 nm.
© 2012 Society of Photo-Optical Instrumentation Engineers (SPIE)
Donald A. Chernoff, David L. Burkhead, "Traceable pitch metrology: supporting the development of patterned media and more," Journal of Micro/Nanolithography, MEMS, and MOEMS 11(1), 011008 (29 March 2012). https://doi.org/10.1117/1.JMM.11.1.011008 . Submission:
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