Sizing Accuracy, Counting Efficiency, Lower Detection Limit and Repeatability of a Wafer Surface Scanner for Ideal and Real-World Particles

Abstract

The performance characteristics of a Tencor Surfscan 4000 wafer surface scanner have been evaluated using ideal polystyrene latex (PSL) spheres and irregularly shaped real-world particles of Si and SiO2. The particles were uniform in size and were deposited on bare silicon wafers and used as standard calibration wafers to study the scanner response. Particles in the 0.1 to 1.0 μm diam range were used. The sizing accuracy, counting efficiency, lower detection limit, and count repeatability of the scanner were studied systematically. The full Maxwell's electromagnetic equations also have been solved numerically on a supereemputer to obtain the light-scattering cross section of the particles on bare silicon wafers. The calculation compares favorably with the experimental results. Because of the high refractive index of silicon, the wafer surface scanner detects Si particles to a considerably smaller size than PSL. The data suggest that Si particles as small as 0.1 μm have been detected by the Surfscan 4000 with 90% counting efficiency even though the nominal lower limit of the instrument is 0.3 μm based on PSL calibration. ？ 1993, The Electrochemical Society, Inc. All rights reserved.