15 November 1996 In-situ simultaneous measurement of temperature and thin film thickness with ultrasonic techniques
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Abstract
We describe a novel technique to measure in situ, simultaneously, temperature and thin film thickness during semiconductor processing. The measurement is based on the principle that the velocity of an ultrasonic Lamb wave propagating in a silicon wafer is a function of both the wafer temperature and the thin film coating on the wafer surface. Because sensitivities of Lamb wave velocity to temperature and film thickness change differently with frequency, with a simple linear inversion method, we are able to obtain both the processing temperature an film thickness simultaneously with two sets of sensors operating at two distinct frequencies, 0.5MHz and 1.5MHz. This technique is demonstrated in an aluminum sputtering system. We have achieved a temperature measurement accuracy of +/- 0.15 degree C and an aluminum film thickness resolution of +/- 170 angstrom. The measurement does not depend on the optical or the electrical properties of either the wafer or the film materials, and is insensitive to the processing environment. With its high measurement accuracy and setup simplicity, this sensor system carries great potential in semiconductor process monitoring and control.
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Butrus T. Khuri-Yakub, Butrus T. Khuri-Yakub, Jun Pei, Jun Pei, F. Levent Degertekin, F. Levent Degertekin, Krishna C. Saraswat, Krishna C. Saraswat, "In-situ simultaneous measurement of temperature and thin film thickness with ultrasonic techniques", Proc. SPIE 2948, Nondestructive Evaluation for Process Control in Manufacturing, (15 November 1996); doi: 10.1117/12.259190; https://doi.org/10.1117/12.259190
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