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Optical Engineering

Real-time image processing techniques for noncontact temperature measurement
Author(s): Michael K. Lang; Gregory W. Donohoe; Saleem H. Zaidi; Steven R. J. Brueck
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Paper Abstract

A noncontact temperature measurement technique based on thermal expansion of materials is presented. The technique, diffraction-order spot analysis, is based on monitoring diffraction angle variations due to grating expansion. Because of the pressing need for noncontact temperature measurements during semiconductor processing, silicon was chosen as the demonstration material. The diffraction method requires a grating of suitable spatial frequency etched onto the surface of the Si wafer. Two symmetrically disposed incident beams are used to provide a differential measurement that is independent of sample tilt to the first order. An automated data acquisition and analysis system was developed for continuous monitoring of two diffraction-order angles. From the order separation, a relative temperature change can be calculated in near real time. Image processing techniques based on centroid operation were used to calculate diffraction-order displacement with subpixel accuracy. For comparison with optical data, simultaneous temperature measurements from a thermocouple bonded to the Si sample were recorded. Good agreement between optical and thermocouple measurements was obtained. Temperature resolution was inversely proportional to the number of grating lines. A resolution of ± 0.37°C is demonstrated for a 3000-line grating over a 20 to 750°C temperature range.

Paper Details

Date Published: 1 October 1994
PDF: 7 pages
Opt. Eng. 33(10) doi: 10.1117/12.179406
Published in: Optical Engineering Volume 33, Issue 10
Show Author Affiliations
Michael K. Lang, Univ. of New Mexico (United States)
Gregory W. Donohoe, Univ. of New Mexico (United States)
Saleem H. Zaidi, Univ. of New Mexico (United States)
Steven R. J. Brueck, Univ. of New Mexico (United States)

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