Process Development and Characterization of Ru-based UBM for In Bumps Integration for Quantum Computing Applications

We present the integration of ruthenium as an interfacial layer between a superconducting seed layer and electroplated indium bumps. Using a dedicated test vehicle and morphological characterizations, this study qualifies the indium electroplating process on top of Ru, and the selective wet etching of ruthenium and the underneath superconducting seed layer. Morphological and electrical characterizations were also conducted to characterize the In/Ru interface and evaluate the formation of intermetallic compounds.