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http://dx.doi.org/10.3807/COPP.2018.2.1.069

Precise Edge Detection Method Using Sigmoid Function in Blurry and Noisy Image for TFT-LCD 2D Critical Dimension Measurement  

Lee, Seung Woo (School of Mechanical and Aerospace Engineering, Seoul National University)
Lee, Sin Yong (School of Mechanical and Aerospace Engineering, Seoul National University)
Pahk, Heui Jae (School of Mechanical and Aerospace Engineering, Seoul National University)
Publication Information
Current Optics and Photonics / v.2, no.1, 2018 , pp. 69-78 More about this Journal
Abstract
This paper presents a precise edge detection algorithm for the critical dimension (CD) measurement of a Thin-Film Transistor Liquid-Crystal Display (TFT-LCD) pattern. The sigmoid surface function is proposed to model the blurred step edge. This model can simultaneously find the position and geometry of the edge precisely. The nonlinear least squares fitting method (Levenberg-Marquardt method) is used to model the image intensity distribution into the proposed sigmoid blurred edge model. The suggested algorithm is verified by comparing the CD measurement repeatability from high-magnified blurry and noisy TFT-LCD images with those from the previous Laplacian of Gaussian (LoG) based sub-pixel edge detection algorithm and error function fitting method. The proposed fitting-based edge detection algorithm produces more precise results than the previous method. The suggested algorithm can be applied to in-line precision CD measurement for high-resolution display devices.
Keywords
TFT-LCD; Critical dimension measurement; Edge detection; Levenberg-Marquardt fitting; Blur edge modeling;
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