Pattern density effect on interfacial bonding characteristics of Cu-Cu direct bonds for 3D IC packages

In this study, effect interfacial bonding strength on pattern density was evaluated. The Silicon oxide(SiO2) on parallel patterned Cu lines wafer can be removed by using a solution of buffered oxide etch and sulfuric acid (BOE/H2SO4) to improve the bonding quality of Cu-Cu pattern direct bonds. Two 8-inch Cu wafers were bonded at 400°C via the thermocompression method. The interfacial adhesion energy of Cu-Cu pattern direct bonding was quantitatively measured by the four-point bending method. After BOE for 2 min/H2SO4 for 1 min wet pretreatment, the interfacial adhesion energies with pattern density of 0.06, and 0.23 were 7.9, and 4.1 J/m2, respectively. Therefore, the CMP planarization is critical to have reliable bonding quality of Cu pattern direct bonds.