Mechanical characterization of wafer level bump-less Cu-Cu bonding

In this paper, the mechanical properties of wafer-level high density Cu-Cu bonding are analyzed. The fabrication flow is optimized based on surface cleanliness, wafer uniformity, W2W alignment accuracy and oxide recess for successful bonding. Post- bonding characterizations include shear test and failure analysis to identify the mechanical strength and failure mechanisms. It is found that failures at Cu-Cu bonding interface are largely attributed to wafer non-uniformity.