title: Improvement of wafer-level Cu-to-Cu bonding quality using wet chemical pretreatment.
abstract: We have evaluated the effect of wet chemical treatment on the interfacial bonding strength of Cu-to-Cu direct bonding. The oxide on a Cu-deposited wafer can be removed by a solution made of hydrofluoric acid and sulfuric acid (HF/H2SO4) or diluted hydrochloric acid (HCl/H2O), which can also improve the bonding quality of Cu-to-Cu bonds. Two 4-inch Cu-deposited wafers were bonded at 250 degrees C via the thermo-compression method. The interfacial adhesion energy of Cu-to-Cu bonding was quantitatively measured by the four-point bending method. After chemical pretreatment for 30 seconds with HF/H2SO4 and HCl:H2O solutions, the measured interfacial adhesion energies were 4.91 J/m2 and 5.51 J/m2, respectively. Microstructural examination of the Cu bonding interfaces showed that the interfacial bonding quality of Cu-to-Cu bonds improved under proper wet chemical etching conditions. Wafer-level cleaning by wet chemical treatment of the Cu surface was found to be a very effective way to improve the bonding quality of Cu bonds, even at bonding temperatures lower than 300 degrees C.
authors: Nano-Mechanical System Rearch Division, Korea Institute of Machinery and Materials, 104 Sinseongno, Yuseong-Gu Daejeon 305-343, Korea (ROK).
authors: Jae-Won
authors: JW
authors: Kim
authors: Seong-Jae
authors: SJ
authors: Jeon
authors: Hak-Joo
authors: HJ
authors: Lee
authors: Seungmin
authors: S
authors: Hyun
authors: Young-Bae
authors: YB
authors: Park