Polarized light scattering from metallic particles on silicon wafers

Polarized light scattering by monodisperse copper and gold spheres, having diameters ranging from 96 nm to 205 nm, deposited on silicon substrates were measured using visible light. The results are compared to an exact theory for scattering by a sphere on a surface, originally developed by Bobbert and Vlieger. The results show that accurate calculation of the scattering of light by a metal sphere requires that the near-field interaction between the sphere and its image be included in a complete manner, that the normal incidence approximation does not suffice for this interaction, and that the existence of any thin oxide layer on the substrate must be included. The polarization of light scattered by these spheres on silicon substrates can be used to determine the size of those spheres. However, uncertainties in the thickness of the substrate oxide layer, roughness of the particles, and uncertainties in the optical properties of the particles may prevent them from being used as standard scatterers. The implementation of the theory, which requires special care when the spheres are metallic and the substrate is highly reflecting, is described in detail.