Low-Temperature Cu-Cu Wafer Bonding

Metal thermo-compression bonding is a process suitable for 3D interconnects applications at wafer level. The process requires typically bonding temperatures of ~400°C and high contact pressure applied during bonding. Temperature reduction below such values is required in order to solve some issues regarding wafer-to-wafer misalignment after bonding and to minimize thermo-mechanical stresses. Low-temperature (LT) Cu-Cu wafer bonding was successfully demonstrated at 175°C. The bond quality, bond strength, metal interface layers microstructure and chemical composition of Cu-Cu wafer pairs bonded under different process conditions were investigated. Experimental results on various Cu native oxide methods evaluation as well as results obtained for various bonding and annealing temperatures are presented.