Polarization of light scattered by particles on silicon wafers

Bidirectional ellipsometry has been developed as a technique for distinguishing among various scattering features near surfaces. Employing incident light with fixed polarization, the technique measures the principal angle of polarization and the degree of linear polarization of light scattered into directions out of the plane of incidence. This technique has been previously shown to be successful at distinguishing between subsurface defects and microroughness. Theoretical models have predicted that the polarization of light scattered by particles should also be different than that scattered by subsurface defects and microroughness. In this paper, experimental results will be presented which show good agreement with these models for a range of sizes of polystyrene latex spheres on silicon wafers. The results demonstrate that the polarization of light scattered by particles can be used to determine the size of particulate contaminants on silicon wafers and other smooth surfaces. The model calculations, based on different degrees of approximation, demonstrate that the mean distance of a particle from the surface is the primary determinant of the scattered light polarization for small scattering angles.