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27 October 1998 Application of a wafer surface scanner to spacecraft contamination control
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Wafer surface scanners, developed and long used in the microelectronics industry for detecting defects on silicon wafers during the semiconductor manufacturing process, have been more recently employed on a limited basis in the aerospace industry to assess particulate debris fallout in cleanrooms and clean work area environments. One use of a wafer scanner in this context is to scan witness plates to obtain data from which to calculate the fraction of a contamination-sensitive surface that is obscured by particulate fallout. Wafer surface scanners have been found to be fast, precise, and straight-forward to sue, but questions about the accuracy of surface area fractions derived rom scanner data have generated controversy in the spacecraft contamination control community. We have examined some commonly used methods for calculating fractional area coverage form scanner data. Geometric midpoint, log-log, and shape-factor models were evaluated for accuracy against a reference standard in the form of area fractions measured using a computer-based image analysis systems, Area fractions calculated using geometric mean diameters of the wafer scanner particle size data produced errors of 0 and +10 percent. Using the log-log mean diameters produced errors of -15 and -20 percent. Shape factor models were found to be inappropriate for use with scanner data.
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Brian K. Blakkolb and Phil Whitesmith "Application of a wafer surface scanner to spacecraft contamination control", Proc. SPIE 3427, Optical Systems Contamination and Degradation, (27 October 1998);

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