Evolution of Cu/Al Intermetallic Compounds in the Copper Bump bonds during Aging Process

Growth of Cu/Al intermetallic compounds (IMCs) at the interface between the copper bond and the Al metallization pad would increase the contact resistance and degrade the bond reliabilities. In this study, the thermosonic copper bump bonds were aged at 250°C for 1 to 196 hours. Then the evolution of Cu/Al IMCs was investigated. Three IMC layers with different colors were found at the Cu/Al interface using the optical microscopy on the xy plane cross-section of the ball bond. The main phases in the Cu/Al IMC are confirmed to be Cu9Al4, and CuAl2. CuAl is believed to be another phase in the copper bond. During the aging process, Cu/Al IMC grew from the periphery of the bond initially and propagated inward to the centre area later. Moreover, some cavities appeared between the IMC layer and bond bottom from the bond periphery and developed into the centre area.