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.