Papers by Author: Shyh Tsong Lin

Abstract: A novel 3-D edge detection methodology is developed to resolve the edge ambiguity problem encountered in 3-D optical surface profilometry employing digital image correlation (DIC). DIC has been surged as a full-field measurement technique for in-plane and out-of-plane dynamic mechanical structure analyses. However, up to date, one of the key issues in DIC is still remained in boundary edge detection since a surface edge is not detectable between two discrete neighboring height jumps due to optical diffraction. Generally, it is common to observe undesirable noisy measured data along surface edges in traditional DIC-based surface 3-D profilometry. To resolve this, a novel random speckle images processing method is established by proposing a new algorithm by employing the multiple symmetric partial template model to determine best edge location with accurate height reconstruction. A theoretical simulation on a pre-calibrated circle target was performed to verify the feasibility of the methodology. Some experiments on real industrial objects having various surface reflective characteristics were implemented to verify its capability on accurate detection of industrial objects having discrete surface edges. From its preliminary evaluation on measurement accuracy, it is found that the maximum measured error on critical dimension can be controlled within less than 6.0% of the overall measuring range while one standard deviation can be kept within less than 1.2%.

Abstract: White light interferometry has become an important method for measuring micro surface profiles with a long vertical range and nano-scale resolution. However, environmental vibration encountered in in-field optical inspection is usually unavoidable and it affects measurement performance significantly. Isolating vibration sources from the measurement system sometimes is not completely effective, especially within complicated in-field fabrication environment. Therefore, in this research we aim to develop a novel method in achieving white-light fringe-locking condition during vertical scanning processes. The developed optical system consists of white light source, a Mirau objective, a PZT vertical scanner, an optical band-pass filter and two image sensing devices. The developed system generates a high and a low coherent interferograms, simultaneously captured by two charged coupled devices (CCDs). The high coherent interferogram is employed to detect high-speed nano-scale displacement and direction of the external vibration. An innovative real time fringe-locking operation is performed and a new vertical scanning technique is performed accordingly to isolate vertical scanning from environmental disturbances. The feasibility of the anti-vibration VSI system is verified by performing some of industrial in-field examples. Based on the experimental result, the fringe locking technique can improve the measurement result.

Abstract: This paper introduces a dual-path Mach-Zehnder interferometer for determining refractive index and geometrical thickness of an optical plate. In this interferometer, two parallel incident beams are separated into two interference pairs which are then recombined to generate two interference signals. An optical plate is placed on the path of one wave of an interference pair, so the phase difference of the interference signals is a function of the plate, and the interferometer is thus able to determine the index and thickness of the plate. A setup constructed to realize the proposed interferometer is described. And the experimental results of applying this setup agree the validity of the interferometer.