In-Situ Investigation of Organic Additive Interactions in Copper Electroplating Solutions with Surface Enhanced Raman Spectroscopy (SERS)

To meet demand for increasingly higher-performance electronics in increasingly smaller form factors, achieving higher logic-memory bandwidth and higher I/O density is required. This necessitates finer copper lines, smaller copper microvias, and fine-pitch, copper-filled through-package vias (TPVs). However, low-quality copper filling in high-aspect ratio TPVs can lead to void formation and mechanical failures. This poses various material and process challenges for the achievement of high-quality copper metallization. These challenges can be addressed through a better understanding of copper deposition mechanisms and investigating the fundamental aspects of copper plating chemistry. In this study, in-situ interactions between different classes of organic additives in copper plating solutions were investigated with surface-enhanced Raman spectroscopy (SERS). A novel test set up is developed which allows for the direct observation of copper plating within a via. SERS was used to observe cases of competitive adsorption between suppressor, leveler, and accelerator additives within this 'via'. These observations are used to infer the impact of different classes of additives on via-filling performance and correlate the electrochemical behavior in the plating cell. A model is proposed to explain the relative tendencies of the differing classes of additives to adsorb to the copper surface within a via.