Acceptance criterion uncertainty during sampling inspection of wafers

Abstract

An analysis has been performed to determine the level of confidence with which contaminated wafers can be detected, depending on the area of the wafer inspected, the cleanliness criterion to pass the inspection, and the probability function for the number of particles likely to be present on the wafer. Particular attention has been paid to the case in which few particles are likely to be present on the entire wafer. It is shown that even 20% relative area inspection provides a highly uncertain estimate of the actual number of particles on the entire wafer under this condition. This uncertain estimate results in an unacceptable number of contaminated wafers passing inspection.