Ultra-fine Cu Wiring Surrounded by Electroless-Plated Ni: Effective Structure for High Insulation Reliable Wiring Applicable to Panel Level Fabrication

Abstract

Abstract Panel level packages such as 2.1D organic interposer and fan-out packages have been attracting the attention as a low cost substrate technology with high density fine wiring layers which interconnect multiple die set side by side. The Cu trench wirings for these packages are usually fabricated by fine and almost rectangular shaped pattern formation of insulation film followed by Ti/Cu sputtering as a seed layer formation, Cu electroplating and CMP. However, sputtering tends to be difficult to deposit on the side wall of almost rectangular shaped pattern. Another challenge is insulation reliability between ultra-fine wirings because electrochemical migration of Cu ion is one of the most serious problems for ultra-fine wirings. Here, instead of seed sputtering, we applied a Ni electroless plating because electroless plating is appropriate to panel process and Ni has high corrosion resistance. Ni seed was uniformly formed on both side wall and bottom of these rectangular patterns. After Cu electroplating, CMP and Ni selective electroless plating on Cu, Cu trench wiring fully surrounded by Ni in 1.5/1.5 μm of line and space was fabricated which has passed biased HAST over 200 h by suppressing corrosion of wiring.