Effects of electrolyte flow direction on height difference in electroplated Cu microstructures for fine-pitch RDL

Abstract

As demand for high-performance and efficient semiconductor chips surges, advanced packaging technologies, such as heterogeneous integration and vertical stacking, are becoming increasingly significant. Among these, the redistribution layer (RDL), essential for connecting chips or packaging elements, is being designed with finer line/space dimensions to meet the growing requirements for I/O access. However, as the width of copper lines decreases to several microns, various fabrication errors arise. Notably, variation in electroplated copper height becomes a significant issue, impacting the overall process. This study analyzes the height deposition differences in copper electroplating that occur at fine-pitch lines (width: 3–11 μm) and proposes a method to mitigate height deviations by adjusting the flow direction of the electrolyte. The results indicate that the deposition height difference between the 3 μm and 11 μm width patterns was reduced from 40% to less than 10%, demonstrating improved reliability in the RDL process by enhancing the uniformity of plating heights across both wide and narrow patterns.