Plasma Cleaning and Thermal Compression Bonding of Indium Bumps as Superconducting Interconnects for Cryogenic and Quantum Computing Applications

This paper introduces a method for direct electrodeposition of indium on superconducting (SC) layers with an optimized electrolyte. Indium-to-indium bump and indium-to-SC layers bonding is achieved using plated wafers. An atmospheric plasma cleaning process removes indium native oxide, and a thermocompression bonding (TCB) process is developed at air, enabling successful bonding of In-In and In-SC layers with different microbumps pitch. Plasma-treated indium bumps exhibit high applicability for successful flip chip bonding at low temperatures in an air atmosphere, as confirmed by cross-section SEM and die shear analysis.