Effect of Wet Pretreatment on Interfacial Adhesion Energy of Cu-Cu Thermocompression Bond for 3D IC Packages

Quantitative analysis of the interfacial adhesion energy of Cu-Cu thermocompression bonds was performed using the four-point bending method with various wet pretreatment conditions. The evaluated interfacial adhesion energies for 1-μm-thick Cu bonding layers were 0.29 J/m2, 1.28 J/m2, 1.64 J/m2, 1.17 J/m2, and 0.43 J/m2 for different acetic acid pretreatment times of 0 min, 1 min, 5 min, 10 min, and 15 min, respectively. There exists an optimum wet etch time for maximum adhesion strength. The change of surface properties with increasing wet etch time was believed to result in the variation of the interfacial adhesion energy. The decrease in interfacial adhesion energy after 5 min seems to result from a decrease in the plastic dissipation energy during interfacial crack propagation with thinner Cu film thickness caused by overetching.