25 April 2008 A Fourier-optics-based non-invasive and vibration-insensitive micron-size object analyzer for quality control assessment
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Abstract
This paper proposes a Fourier-Optics-based non-invasive quality assessment tool for a micron-thick bar. Our design concept relies on a transmissive optical architecture to reduce the effect of an object's angle misalignment that can introduce a significant measurement error. From the far-field diffraction pattern of the micron-thick bar, we determine its thickness from the distance either between the two adjacent diffracted order beams or between a high order diffracted beam and the zero order beam. In addition, because all diffracted order beams are aligned, we use the resulting slope to determine the edge parallelism. The amount of edge defect on the sample can be investigated by evaluating the distribution of the optical intensity inside diffracted order beams. Our theoretical analysis indicates that for a 238-μm thick bar, our proposed concept provides better than 1 μm and 0.1° resolutions in thickness and edge parallelism measurements. Our experiment using a 635-nm wavelength laser diode and 22 sample bars with an average thickness of 238-μm shows that our approach can simultaneously evaluate the thickness and the edge parallelism of the bar samples as well as distinguish nicely edged bars from poorly edged bars. Key features include low cost, ease of implementation, robustness, and low component counts.
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Sarun Sumriddetchkajorn, Kosom Chaitavon, "A Fourier-optics-based non-invasive and vibration-insensitive micron-size object analyzer for quality control assessment", Proc. SPIE 6995, Optical Micro- and Nanometrology in Microsystems Technology II, 699511 (25 April 2008); doi: 10.1117/12.779149; https://doi.org/10.1117/12.779149
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