Impact of Electroless-Ni Seed Layer on Cu-Bottom-up Electroplating in High Aspect Ratio (>10) TSVs for 3D-IC Packaging Applications

The electroless (EL) Ni layer conformally formed inside the high aspect ratio (AR, >10) through-Si-via (TSV) has been investigated for its role as seed layer in bottom-up Cu electroplating. From the electro-chemical adsorption monitoring data it was found that the adsorption (or accumulation) of additives onto the EL-Ni surface for bottom-up Cu electroplating was prodoundly suppressed when compared with the Ni seed layer depositied by PVD. A simple and viable two step process was proposed and demonstrated to overcome the problem, and we were able to successfully fill the TSVs (width ~10 mm, AR > 10) with by Cu-electroplating using the EL- Ni as seed as well as barrier layer. Thus, this low-cost, readily-scalable (both in wafer-size and volume) and CMOS compatible EL method for the formation of Ni barrier-cum-seed layer in the high AR TSVs for integration and packaging applications has tremendous potential to replace the high-cost PVD or CVD barrier and seed layers..