Annealing temperature effect on the Cu-Cu bonding energy for 3D-IC integration

Interfacial adhesive energy was evaluated quantitatively in relation to the bonding temperature and subsequent thermal treatment to develop a Cu-Cu thermal compressed bonding process at low temperature for a three-dimensional integration circuit (3D-IC) package. Two pieces of sputtered Cu films coated on a Si wafer were bonded at 300 °C, 350 °C, and 400 °C. A high bonding temperature increased the interfacial adhesive energy, and the original interfacial layers of Cu film gradually disappeared, as observed in focus ion beam (FIB) images. Specimens of Cu to Cu bonding were thermally compressed at 300 °C and were post-annealed at 200 °C, 250 °C, and 300 °C in a N2 environment for 1 h. As a result, the original interfacial layer of Cu disappeared at 300 °C, and an interfacial adhesive energy value above 10 J/m2 was obtained.