Mechanism study on nanometric finishing of copper by electrochemical polishing using sulfuric acid/methanol electrolyte

To eliminate surface defects in copper-based microstructures produced through micromachining technology and to further decrease surface roughness, subsequent polishing treatments are essential for the fabricated microstructured components. Electrochemical polishing (ECP) is a noncontact polishing method that minimizes surface damage. Nevertheless, traditional copper ECP methods have limitations such as complex electrolyte compositions, low polishing efficiency, and difficulties in achieving nanoscale roughness. Currently, research on ECP for copper primarily focuses on process optimization, due to the limited understanding of the morphology and composition of intermediate products formed during the process. This study presents a comprehensive approach involving the development of a sulfuric acid/methanol electrolyte for the ECP of copper. Process parameters were optimized to increase the efficiency of copper polishing. Additionally, a new polishing model was proposed to elucidate the material removal mechanism of copper. The formation and removal rates of the passivation film were faster at the high points, and this results in differences in the material removal rates at high and low points, thereby achieving polishing. Under optimal conditions, the Sa surface roughness of copper was reduced from 83.5 nm to 2.6 nm within only 3 min. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) revealed that the passivation film primarily consisted of Cu 3 (SO 4 ) 2 (OH) 2 ·2H 2 O and CH 3 CuS. This research demonstrates that ECP offers a promising method for efficiently and effectively polishing copper to high standards.