Microstructure evolution and abnormal grain growth during copper wafer bonding

Evolution of microstructure morphologies and grain orientations of Cu-Cu bonded wafers during bonding and annealing were studied by means of transmission electron microscopy, electron diffraction and X-ray diffraction. The bonded Cu grain structure reaches steady state after post-bonding anneal. An abnormal (220) grain growth was observed during the initial bonding process. Upon annealing, the preferred grain orientation of the whole film shifts from (111) to (220). The effects of yielding and energy minimization may are possible reasons for the evolution of the preferred grain orientation.