Non-specular scattering of carriers from surface defects in thin metal interconnects

Non-specular scattering of carriers, despite being one of the key contributors to metal film resistivity, is conveniently characterized by a single parameter p (referred to as specularity parameter) in the literature without providing a means to separate out relative contributions of surface defects to it. In this work, we report a theoretical formalism to predict contributions to (non-specular) reflection (scattering) of carriers from different types of chemical and structural defects on the film surface. Establishing specular reflection as a special case of the more generalized reflection from the surface, we show that elastic scatterings contribute to the non-specular reflections by randomizing the forward momentum along the transport direction. We predict density and angle-dependent specularity coefficient for various types of defects and show that large angle reflections tend to be non-specular in the presence of isotropic surface defects. Using this formalism, we predict the probability of specular reflection for technologically relevant metal–metal and metal–insulator interfaces. Calculated specularity coefficients are in agreement with values obtained from experimental measurements. Our methodology will help in designing next generation interconnects and engineering the interfaces with minimal diffuse reflection.