The impact of cations on nucleus density during copper electrodeposition

High nucleus density is among the most important factors in determining the success of the direct-copper-electrodeposition technique. A group of inorganic species including potassium sulfate (K2SO4), sodium sulfate (Na2SO4), magnesium sulfate (MgSO4), and copper sulfate (CuSO4) were investigated in terms of their impact on copper nucleus density during galvanostatic electrodeposition of copper onto foreign substrates. Newly formed copper nuclei on the substrate were observed using scanning electron microscopy (SEM) and then manually counted to obtain nucleus density data. Results show that in the presence of K2SO4, copper nucleus density can be increased by a factor of up to 7, while Na2SO4 may lead to at least double increase of nucleus density. Electroanalysis indicates that the overpotential increase as a result of adding relevant sulfate salts may account for the increased nucleus density.