Effect of an ultrasonic field on the nucleation and growth mechanism of electrodeposited Cu thin films on a magnetron sputtered Cu layer

Abstract

Composite copper foil and ultra-thin copper foil are prepared through the synergistic application of magnetron sputtering and electrodeposition techniques. The adhesion between the substrate and electrodeposited layer is enhanced by the magnetron sputtered seed layer. However, pores and pits are found in the electrodeposited layer, which severely affect the final surface quality and performance of the foil. The ultrasonic field exhibits a unique effect in improving the morphology and performance of the electrodeposited layer. Based on this, a magnetron sputtered Cu layer was selected as the substrate, and gradient ultrasonic power experiments were designed. Through combined electrochemical performance testing and microstructure characterization, the influence of ultrasonic field power on the electrochemical behavior of the electrodeposited Cu film in the sulfate system was investigated; meanwhile, the nucleation and growth mechanism was elucidated. The results show that the mass transfer process of Cu(II) in the electrolyte is significantly enhanced by the “cavitation effect” and “mechanical vibration effect” of the ultrasonic field. Under the mass transfer effect of the ultrasonic field, the deposition reaction is transformed from diffusion controlled to electrochemically controlled, and the deposition rate increases. Meanwhile, the application of an ultrasonic field increases the nucleation rate of Cu, changes the crystal orientation and grain size of the Cu film, and reduces the charge transfer resistance, thus obtaining a more uniform and dense Cu film.