(invited) Copper Electroplating Technology for Packaging

Copper pillar is a transformative technology for next generation 2.5D/3D packaging.  Fine-pitch copper pillar bumps have replaced conventional flip chip solder bumps when the need for extremely low profile, high connectivity interconnect is required.  Cu pillar Flip-Chip is expected to grow at a 35% CAGR between 2010 - 2018 in terms of wafer count.  It will be a key interconnect technology in future semiconductor packages.  However, it is not just copper deposition into vias, but also needs high speed trough-mask wafer plating, high uniform bump height, flat bump shape, good surface morphology and electric reliability.  Copper deposition in microvias is effected by electric field which is photoresist shielding causing “current distribution”.  A bump center has higher current density than peripheries, so the shape will become convex.  The inner microvia flow field is another factor which causes higher copper ion concentration at center and forms a domed bump.  Although, these two factors will cause a convex bump shape, additives can influence the electroplating behaviors.  Commercial additives can let bump shape become very flat, but it needs stable flow system and small dosage windows.  CUPUR U is a unique package which can control bump shape by one additive concentration.  It can selectively inhibit the bump center current distribution, let domed bump shape becomes flat, even dimple or dish shape. This property is not only controlling bump shape, but also improve the uniformity.  They can be used in high flow system, high current density (> 20 ASD) and wide dosage windows in copper sulfate system.  The package can be used on other BEOL application, such as micro-bump, RDL, UBM at high speed plating.