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Proceedings Paper

An auto-focusing system for white light microscopic measurement
Author(s): Ming Chang; Juti Rani Deka; Pei Jung Chen; Yu Kuan Chen; Changcai Cui
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Paper Abstract

With the rapid development of semiconductor technology the demand for high resolution measuring system is evolving at an ever-increasing pace. Microscope was initially used to detect the defect by connecting charge couple device (CCD) as an auxiliary device. In general, for microscopic measurement human eyes are used to focus on the sample. The adjustment depends on the operator's astute measurement ability, which affected the repeatability and accuracy of the readings. There is a need of high-speed microscope auto focusing system for industrial applications. The present investigation describes about the development of an autofocus system to carry out microscopic measurement more precisely and accurately with less time. The measurement system consists of a light source, two beam splitters, a movable sample stage and a Mirau's interferometer, a photo-detector and 8051 microcontroller (MCU89C51). The light reflected from the sample surface interferes with the light reflected from the reference and produce an interference pattern, which is imaged onto a CCD array. In the setup developed for the autofocus one extra beam splitter is placed in the path of interfered beam to the CCD. The beam splitter is placed at equal distances from the CCD and the photodetector. The focus position is determined from the voltage developed in the photo-detector due to the movement of sample stage of the microscope. The maximum voltage that obtained at the focus position is confirmed with the CCD image. Microcontroller is used to stop the controller at the focus position immediately once the sample stage reaches it. Software is developed to locate the maximum intensity position. The design may autofocus the interferometer within 4mm distance in 1 second. The auto-focusing not only provides enhanced repeatability and accuracy of the results at a faster rate but also minimizes operator involvement.

Paper Details

Date Published: 31 December 2008
PDF: 6 pages
Proc. SPIE 7130, Fourth International Symposium on Precision Mechanical Measurements, 71302T (31 December 2008); doi: 10.1117/12.819660
Show Author Affiliations
Ming Chang, Huaqiao Univ. (China)
Chung Yuan Christian Univ. (Taiwan)
Juti Rani Deka, Chung Yuan Christian Univ. (Taiwan)
Pei Jung Chen, Chung Yuan Christian Univ. (Taiwan)
Yu Kuan Chen, Chung Yuan Christian Univ. (Taiwan)
Changcai Cui, Huaqiao Univ. (China)

Published in SPIE Proceedings Vol. 7130:
Fourth International Symposium on Precision Mechanical Measurements
Yetai Fei; Kuang-Chao Fan; Rongsheng Lu, Editor(s)

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