<title>Use of light scatter signals to identify particle material</title>

Defect detection and counting have been used to qualify silicon wafers for use in device production for several years. Defect sizing is attempted by comparing scatter signals, used for detection, to signals produced from spherical polystyrene latex spheres of known diameter. Real particles are neither spherical nor made of plastic, and scatter differently. This paper addresses the issue of spherical particle material identification through the measurement of scatter signals into several directions. The basic idea is that the average diameter and material constants comprising the complex index amount to three unknowns. The question is whether they can be estimated from three independent measurements. The results presented here are quite positive. The issue of particle shape is left for another paper.