Effects of Polyethylene Glycol and Chloride Ion on Copper Electroplating at High Current Density

To determine the effect of Polyethylene Glycol(PEG) and Chloride ions(Cl-) as additives during electroplating, this study used interaction plots of various characteristics of the electroplated Cu foils for analyses. Crystals of about 2 µm in size were observed on the surface of Cu electroplated in the electrolyte without PEG. When 30-100 ppm PEG was added, the crystal size and surface roughness decreased in relation to the amount of PEG. However, there were lots of dented areas, which became fewer as Chloride ions were increased from 20 ppm to 40 ppm. When 300 ppm PEG was added, the dented areas were not observed. Nevertheless, the surface morphology was very irregular and rough. In the group with 30-100 ppm PEG added, the resistivity decreased due to the increase in grain size. Moreover, the tendency of crystals to grow preferentially in the direction of the (111) plane led to an increased resistance to EM(electro-migration). When 40 ppm of chloride ions and 100 ppm of PEG were added, the yield strength increased by 22.4%, the tensile strength increased by 28.7%, and the elongation increased by 293.5% compared to the group without additives. This study showed that a combination of appropriate additives and amounts was required to form copper foils with low surface roughness, excellent electrical properties, and EM resistance and low corrosion rate. Therefore, with 100 ppm added PEG, it is necessary to add 20 ppm of chloride ions to ensure a low corrosion rate and 40 ppm of chloride ions for high mechanical properties.