Study on process optimization and suppression methods for wafer-level electroplated copper nodule defects

Purpose This study aims to investigate the issue of nodule formation during wafer-level copper electroplating and explore corresponding mitigation strategies. Through experiments involving wafers with different opening areas and modified electroplating process parameters, the underlying causes of nodule formation were revealed, and engineering solutions were proposed. This research holds significant importance for enhancing the stability of the wafer-level copper electroplating process and the reliability of the packaging structure. Design/methodology/approach A multi-dimensional validation experimental scheme was designed: systematic and comprehensive research into the causes of wafer-level electroplating nodules and process optimization methods was conducted from three perspectives – root cause investigation, reproduction of copper nodule defects and process optimization approaches. Furthermore, the overall reliability of the electroplated layer structure and the solder ball structure of the improved process samples was verified through a solder ball placement and reflow process on the plated samples. Findings The study indicates that the severity of copper nodule defects in wafer-level electroplating is inversely proportional to the electroplating area. The nodule issue can be effectively mitigated through three methods: increasing the electroplating area on the wafer by adding dummy pads; applying a small cathode current as the wafer enters the electroplating bath; and shortening the immersion delay time while using a low current density in the initial stage to address seed layer damage. Originality/value This research provides an important reference for achieving smooth copper deposition in wafer-level electroplating. Through uniformity testing and comparative experiments before and after wafer immersion in the electroplating solution, it was identified that the primary cause of copper nodules is the corrosion damage of the seed layer metal induced by the “galvanic effect.” An easily implementable process improvement method is proposed by reducing the delay time and adopting a low-current-density initial plating step, the number of nodule defects on test samples can be reduced by 80%.