Effects of Current Density and Organic Additives on via Copper Electroplating for 3D Packaging

Abstract

【In an effort to overcome the problems which arise when fabricating high-aspect-ratio TSV(through silicon via), we performed experiments involving the void-free Cu filling of a TSV(10~20 ${\mu}m$ in diameter with an aspect ratio of 5~7) by controlling the plating DC current density and the additive SPS concentration. Initially, the copper deposit growth mode in and around the trench and the TSV was estimated by the change in the plating DC current density. According to the variation of the plating current density, the deposition rate during Cu electroplating differed at the top and the bottom of the trench. Specifically, at a current density 2.5 mA/ $cm^2$ , the deposition rate in the corner of the trench was lower than that at the top and on the bottom sides. From this result, we confirmed that a plating current density 2.5 mA/ $cm^2$ is very useful for void-free Cu filling of a TSV. In order to reduce the plating time, we attempted TSV Cu filling by controlling the accelerator SPS concentration at a plating current density of 2.5 mA/ $cm^2$ . A TSV with a diameter 10 ${\mu}m$ and an aspect ratio of 7 was filled completely with Cu plating material in 90 min at a current density 2.5 mA/ $cm^2$ with an addition of SPS at 50 mg/L. Finally, we found that TSV can be filled rapidly with plated Cu without voids by controlling the SPS concentration at the optimized plating current density.】