Effects of additive interactions on electroplating profile of IC substrate copper pillars

Copper pillars exhibit great performance advantages beyond ball gird array (BGA) for large-area, finepitched and high-density interconnects in flip-chips, system in package (SiP) and 3D packaging. The development of miniaturized chips and heterogeneous integration demand for both high efficiency and high quality in electroplated copper pillars. A controllable flat or dished pillar profile is in favor of stabilizing solder balls during reflow, otherwise molten solder may flow off. Developing high-performance organic additives, including accelerators, suppressors and levelers, grains much attention in copper electroplating industry, which plays an important role in affecting electrode kinetics and deposit morphologies. However, as high current densities (>8 Adm
^-2
) are applied in copper pillar electroplating, it brings a challenge to profile control that its top surface tend to dome due to breakdown of inhibitory additive ensembles. In present work, a self-developed copolymeric leveler is formulated with prototypical bis- (sodium sulfopropyl)-disulfide (SPS) accelerator and polyethylene glycol (PEG) suppressor to electroplate integrated circuits (IC) substrate copper pillar, with the multi-additive adsorption and interaction mechanisms revealed. As a result, flat copper pillars (size: 180×240 μm) can be achieved within a high current density range of 15 Adm
^-2
. Moreover, domed to dished profile of copper pillars are found to depend on the pattern size and can be tuned by tuning controlling the accelerator-to-leveler ratio.