Effect of Reverse Currents during Electroplating on the ⟨111⟩-Oriented and Nanotwinned Columnar Grain Growth of Copper Films

Nanotwinned copper (nt-Cu) has been attracting a great deal of attention in the past decades due to its excellent mechanical and electrical properties. In this study, a new approach, periodic-reverse (PR) waveforms, is adopted to electroplate nt-Cu films with highly ⟨111⟩ oriented columnar grain microstructures. We investigate the effect of the reverse current on the microstructures of ⟨111⟩-oriented nt-Cu films and their grain growth behavior. With proper reverse current parameters, we are able to obtain a nt-Cu film with a significantly thin transition layer, low amount of impurities, and low residual stress levels in comparison to a DC electroplated film. It is also discovered that the grain size after annealing of the nt-Cu film is related to its initial columnar grain microstructures, which can be tailored by the reverse current parameter. These results show that PR electroplating provides a promising approach in improving and controlling the microstructures and properties of nt-Cu films.