Focus and edge detection algorithms and their relevance to the development of an optical overlay calibration standard

Stephen H. Fox; Richard M. Silver; Edward Kornegay; Mario Dagenais

doi:10.1117/12.350794

14 June 1999 Focus and edge detection algorithms and their relevance to the development of an optical overlay calibration standard

Stephen H. Fox, Richard M. Silver, Edward Kornegay, Mario Dagenais

Author Affiliations +

Proceedings Volume 3677, Metrology, Inspection, and Process Control for Microlithography XIII; (1999) https://doi.org/10.1117/12.350794
Event: Microlithography '99, 1999, Santa Clara, CA, United States

Abstract

We present results of investigations into optical focus and edge detection algorithms relevant to overlay metrology. We compare gradient energy, standard deviation, contrast and summed intensity of acquired images as focus metrics for bright-field, scanning confocal, and confocal microscopy. For our purposes, gradient energy calculated via Sobel filtering was found to be the best criterion for an autofocus algorithm. We predict, based on theoretical results, that all of the focus algorithm we considered will focus in different heights relative to the object depending on the material properties of the object. Edge detection is accomplished via a window and spline technique for whole image data, and by application of a multiple line regression algorithm for single scan data. Measurements accomplished through these techniques are compared to state of the art scattering and analysis models.

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Stephen H. Fox, Richard M. Silver, Edward Kornegay, and Mario Dagenais "Focus and edge detection algorithms and their relevance to the development of an optical overlay calibration standard", Proc. SPIE 3677, Metrology, Inspection, and Process Control for Microlithography XIII, (14 June 1999); https://doi.org/10.1117/12.350794

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