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19 July 1989 Optical Measurement Of Contacts
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Optical measurement of contacts and vias is possible because when a microscope is focused at a plane near to the bottom of a contact, light is reflected from the bottom and forms a characteristic image: a dark ring surrounding a brighter center. The dark ring image is common to a variety of substrates, including resist on poly, etched metal, nitride, resist on doped glass on grainy metal, etc.. Using image processing and dedicated measurement algorithms, it is possible to separate the dark ring from the brighter center by a "contour" or edge, and to measure the diameters (in x or y) and the area inside the contour. Also, by comparing these measurements against reference measurements it is possible to determine if the contact is open or closed. These measurements can be repeated with precision between .01 and .02 microns (depending on materials) and can be calibrated to a standard such as a SEM or an electrical test.
© (1989) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Peter Waksman "Optical Measurement Of Contacts", Proc. SPIE 1087, Integrated Circuit Metrology, Inspection, and Process Control III, (19 July 1989);

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