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22 March 2008 Overlay measurement based on dual-overlay grating image
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We develop a novel target, dual-overlay grating, used in the overlay measurement with an optical bright-field imaging tool. The dual-overlay grating is the combination of two overlay gratings with different pitch. The two overlay grating are approached each other and the separation gap between them is sub-micrometer. The image in the proximity of the boundary of two overlay gratings is measured at in-focus position, and a method is built to analyze the image. The gradient value of image and a merit value are calculated. A series of dual-overlay grating is measured and analyzed with different overlay offset. We found the relation between the merit value and overlay offset is linear in certain region, and the dual-overlay grating has the nano-scale resolution to the overlay offset. Thus, the dual-overlay grating has potential application in overlay metrology for the process control in the future semi-conductor manufacturing.
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Deh-Ming Shyu, Yi-sha Ku, and Shu-Ping Dong "Overlay measurement based on dual-overlay grating image", Proc. SPIE 6922, Metrology, Inspection, and Process Control for Microlithography XXII, 69220Q (22 March 2008);

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