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.