Size effects on the optimization of the mechanical resistance and the electrical conductivity of Cu thin films

Abstract

Cu thin films are nowadays attractive components for emergent MEMS based technologies because their high electrical conductivity (σ) and good mechanical properties. In general, σ is negatively affected when the film thickness (t) decreases close to the electron mean free path (le) scale and the mechanical resistance is favored. So, we propose a study of the Cu thin films optimum size conditions to achieve a well-compromise between the mechanical and electrical performance. Films mechanical behavior was studied by Atomic Force Microscopy (AFM) assisted nanoindentation. Results showed considerable increments of the elastic (Ue)-to-total (Ut) strain energy ratios (Ue/Ut) from 0.27 ± 0.02 up to 0.54 ± 0.04 as t was decreased from 2 [µm] to 100 [nm], evidencing a clear films mechanical resistance improvement by reducing t. Our analysis showed that the improvement of the films mechanical resistance easily compensates the negative impact on the electrical conductivity, especially for t>le.