13 September 2012 Self calibration for slope-dependent errors in optical profilometry by using the random ball test
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Abstract
Current commercial height profile measuring instruments, e.g. the confocal microscope and, the white light interferometer, are widely used in both research institutes and industry. The systematic error of such instruments can be the same order of magnitude as features on the surface to be measured, if care is not taken with calibration. Instrument error in most cases depends on the surface slope. Thus, calibration of the instrument is important. The random ball test, proposed by Parks et al, is a self calibration technique for transmission sphere calibration in phase shift interferometry. The idea is, by measuring a collection of random patches on the surface of a sphere and then averaging the results, the contributions from the ball go to zero leaving only the systematic biases due to the instrument. This paper shows it can also be used to calibrate slope-dependent errors in profilometers such as the scanning white light interferometer (SWLI). This will be demonstrated with both simulation and experimental results. For example, with a commercial SWLI measurement with a 20X objective, our random ball test indicates that the height error can be as large as 250 nm at a slope value of 2.9 degrees when using the envelope peak algorithm for analysis. Similarly, with a confocal microscope measurement using a 50X objective, the height error can be as large as 800 nm at a slope value of 12.1 degrees. These slope-dependent errors can be used to compensate future sloped-surface measurements.
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Yue Zhou, Young-Sik Ghim, Angela Davies, "Self calibration for slope-dependent errors in optical profilometry by using the random ball test", Proc. SPIE 8493, Interferometry XVI: Techniques and Analysis, 84930H (13 September 2012); doi: 10.1117/12.928504; https://doi.org/10.1117/12.928504
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