The effects of ultrasonic agitation on supercritical CO2 copper electroplating

Applying ultrasound to the electroplating process can improve mechanical properties and surface roughness of the coating. Supercritical electroplating process can refine grain to improve the surface roughness and hardness. However, so far there is no research combining the above two processes to explore its effect on the coating. This study aims to use ultrasound (42 kHz) in supercritical CO2 (SC-CO2) electroplating process to investigate the effect of ultrasonic powers and supercritical pressures on the properties of copper films. From the results it was clear that higher ultrasonic irradiation resulted in higher current efficiency, grain refinement, higher hardness, better surface roughness and higher internal stress. SEM was also presented to verify the correctness of the measured data. The optimal parameters were set to obtain the deposit at pressure of 2000 psi and ultrasonic irradiation of 0.157 W/cm3. Compared with SC-CO2 electroplating process, the current efficiency can be increased from 77.57% to 93.4%, the grain size decreases from 24.34 nm to 22.45 nm, the hardness increases from 92.87 Hv to 174.18 Hv, and the surface roughness decreases from 0.83 μm to 0.28 μm. Therefore, this study has successfully integrated advantages of ultrasound and SC-CO2 electroplating, and proved that applied ultrasound to SC-CO2 electroplating process can significantly improve the mechanical properties of the coating.