Surface and grain boundary scattering studied in beveled polycrystalline thin copper films

Abstract

The inverse relationship between film thickness and electrical resistivity of metallic films is usually studied by depositing a series of films with different thickness and measuring their sheet resistance with a four-point probe. However, the structure and uniformity of polycrystalline thin films typically depend on thickness, rendering it difficult to establish the dominant electron scattering mechanism. In order to circumvent the uniformity issue we now use beveled films to establish the thickness dependent resistivity of thin copper films. Here the resistivity of films down to a few nm’s can be studied without, e.g., a percolation effect. Additionally, the comparison of data obtained on samples where beveling took place either before or after anneal is used to study the impact of grain size on resistivity. It is shown that the normally observed strong increase in resistivity is dominated by grain boundary scattering. However, the influence of surface scattering can be clearly observed when thick films are thinned after a high temperature anneal in which case the grain size is considerably larger than the electron mean free path of copper at room temperature.