Pulse-Electrodeposition and Growth Mechanism of Nanotwinned Copper Nanowires inside High Aspect-Ratio Anodic Aluminum Oxide

Abstract

Nanotwinned copper (nt-Cu) has proven to possess many fascinating physical/chemical properties. However, it is still challenging to control the twin density and its orientation especially for high aspect-ratio Cu vias. Here, a matrix of nt-Cu nanowires (aspect ratio > 150) with dense coherent twin boundaries (CTBs) perpendicular to the growth direction were deposited in porous anodic aluminium oxide vias by pulse electrodeposition. We changed the pulse on/off duration to control the degree of (111) growth texture and twin density of the nt-Cu nanowires. A small anodic current in the pulse-off period enhanced (111) crystal texture and CTB formation during the bottom-up filling process. With the analysis of twin density, we proposed that the nanoscale twinning was activated by facet-dependent crystal growth and stress accumulation/relaxation behaviour during pulse electrodeposition. The interplay between on/off period and bias potential could modulate the twin density. Also, the sulfate adsorbates were proved to play an important role in the stress accumulation process. This study could be implemented in fabricating Cu interconnect in nanoelectronic devices and nanoelectromechanical systems. Figure 1