Twin spacing manipulation of (111)-oriented nanotwinned copper via aeration flow control in a high-speed direct-current electroplating system with thiol organic additives

It is a challenge to develop a cost-effective and time-efficient process for manufacturing nanotwinned copper foil with the precise control of twin spacing, a crucial determinant of nanotwinned copper properties. In this work, we modify the aeration flow rate near the cathode to adjust the mass transfer effects of chloride ions and 3-mercapto-1-propanesulfonate (MPS) in an acidic CuSO₄ system. These modifications can change the copper crystallization and morphology of copper deposits, promoting the twin boundary formation. In particular, at a high plating current density of 40 A dm⁻² and 10 °C in a direct current (dc) mode, the twin lamella distribution in the copper deposit with the twin spacing centered at ca. 136 nm can be simply narrowed down to 61 nm by increasing the aeration flow rate from 0.5 to 2.5 L min⁻¹. The microstructures of copper foil have been examined using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), ion-channeling images, an alpha-step profiler, atomic force microscopy (AFM), and electron backscatter diffraction (EBSD).