In-situ observation and electrochemical studies on copper pillar bump filling process

Electrodeposition plays an indispensable role in microelectronic process. Copper pillar bumps (CPBs) have received widespread attention in advanced packaging. Clarifying the effects of additives is essential to obtain the uniform, leveling and void-free filled layer. However, the observation platform to achieve efficient screening of various additive combinations is absent. Herein, taking advantage of the highly transparent characteristic of microcavity electrode (MCE) as well as its similarity to the practical working conditions of CPBs, the convection-dependence of the copper filling layer (500-25 mu m, aspect ratio similar to 1) was observed. The leveling effect of the additives with the modulating flow and electric fields was visualized. In-situ observations and electrochemical evidences support that accelerated growth of the downstream front can only be observed when all three organic additives are present simultaneously. Although the introduction of convection can accelerate the renewal of additives on the surface of the filled layer, the antagonistic effect of Janus Green B (JGB) on sodium 3,3 '-disulfanediylbis(propane-1-sulfonate) (SPS) is weakened due to the rapid decomposition of JGB within the microcavity, thereby amplifying the accumulation effect of SPS downstream in the microcavity. Consequently, the competitiveness of SPS against polyethylene glycol (PEG) on that side (depolarization) is enhanced, and a non-uniform distribution of the filled layer is established. As the protrusion approaches the mouth of the microcavity, the sufficient supply of JGB reverses the height bias. This work demonstrates the value of this in-situ observation platform in parameters optimizing and mechanisms studying.