Effect of ultrasonic field on nucleation and growth mechanism of electrodeposited Cu thin film on magnetron sputtered Cu layer

Abstract

The composite copper foil and ultra-thin copper foil is prepared through the synergistic application of magnetron sputtering and electrodeposition techniques. The adhesion between the substrate and electrodeposited layer is enhanced by magnetron sputtered seed layer. However, pores and pits are found in the electrodeposited layer, which severely affects the final surface quality and performance of the foil. The ultrasonic field exhibits a unique effect in improving the morphology and performance of electrodeposited layer. Based on this, 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 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 "cavitation effect" and "mechanical vibration effect" of ultrasonic field. Under the mass transfer effect of ultrasonic field, the deposition reaction is transformed from diffusion controlled to electrochemically controlled, and the deposition rate increases. Meanwhile, the application of ultrasonic field increases the nucleation rate of Cu, changes the crystal orientation of Cu film, reduces the charge transfer resistance, thus obtaining more uniform and dense Cu film.