Low resistive copper films deposited using the ion beam sputtering method with an ultra-high purity target

Abstract

Electric conductivities of copper thin films were investigated aiming toward low-loss metallization materials in energy-saving MEMS devices. The copper thin films were deposited with the goal of reducing impurities significantly and expecting to minimize scattering cross sections by relevant exclusion of scattering factors such as crystalline grain boundaries. Electron cyclotron resonance ion beam sputtering deposition (ECR-IBS) using an ultra-pure copper target was employed as the film process. Two indexes of the conductive properties, i.e. the resistivity at direct current and the mean free time extracted from optical transmission/reflection measurements at the plasma frequency, were employed in the evaluations and optimum conditions of the thin film processing were investigated. As a result, significant improvement in conductivity using the optimized conditions of temperature (430 K) and purity of the target (8N) was achieved for a thickness range of 10–300 nm.