Fast cross section reconstruction for metallic sub-micron wires on a substrate

We present a fast, Kirsch-Kress type numerical inversion method for shape reconstruction of metallic sub-micron wires/rods on substrates. For increased speed of inversion, the numerical integration occurring in the forward scattering model, the far-field matching and the half-space Green's function is simplified: the surface current densities in the radiation integrals are approximated by spatially impulsive sources, matching of the sources with the measured scattered far field is done at discrete testing points, and finally, the half-space Green's function, accounting for the presence of the substrate, is approximated using Fresnel reflection and complex image theory. The wires/rods to be reconstructed are modeled using the Surface Impedance Boundary Condition (SIBC). We apply the inversion method to experimental angular-resolved bistatic scatterometric data (BRDF), measured at the Danish Fundamental Metrology using a 325 nm He-Cd laser. The cross-sections of three platinum (Pt) sub-micron wires on silicon (Si) substrate are estimated from the far-field BRDF data. In addition, we present an analysis of the accuracy and efficiency of the inversion for families of circular perfectly electrically conducting and silver (Ag) submicron wires on Si substrate, using numerically simulated measurement data.