Verifying the Calibration of Optical Particle Counters below 100 nm
By David Blackford, Ph.D., Gary Van Schooneveld, and Don Grant
INSTRUMENTS MONITORING SEMICONDUCTORS
Abstract
Optical particle counters (OPCs) are critical for monitoring particle contamination in the ultrapure water (UPW*) used to manufacture semiconductors. However, OPCs from different manufactures rarely correlate with each other because the manufacturers use different wavelengths, different angles of collection, and different definitions of illuminated area from each other. Currently, all OPCs are calibrated using polystyrene latex (PSL) spheres. An OPCﾒs response to real particles in UPW is therefore based on how an OPC measures light scattered from white, plastic spheres suspended in UPW. PSL spheres are an unrealistic, but convenient calibration material for OPC calibration. An alternative name for OPCs could be ﾓscattered-light event monitors,ﾔ as OPCs measure an equivalent particle size based on a PSL calibration.
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