title: Low-temperature direct copper-to-copper bonding enabled by creep on (111) surfaces of nanotwinned Cu.
abstract: Direct Cu-to-Cu bonding was achieved at temperatures of 150-250 °C using a compressive stress of 100 psi (0.69 MPa) held for 10-60 min at 10(-3) torr. The key controlling parameter for direct bonding is rapid surface diffusion on (111) surface of Cu. Instead of using (111) oriented single crystal of Cu, oriented (111) texture of extremely high degree, exceeding 90%, was fabricated using the oriented nano-twin Cu. The bonded interface between two (111) surfaces forms a twist-type grain boundary. If the grain boundary has a low angle, it has a hexagonal network of screw dislocations. Such network image was obtained by plan-view transmission electron microscopy. A simple kinetic model of surface creep is presented; and the calculated and measured time of bonding is in reasonable agreement.
authors.affiliation: Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, 30010 Taiwan, R.O.C.
authors.forename: Chien-Min
authors.initials: CM
authors.lastname: Liu
authors.affiliation: Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, 30010 Taiwan, R.O.C.
authors.forename: Han-Wen
authors.initials: HW
authors.lastname: Lin
authors.affiliation: Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, 30010 Taiwan, R.O.C.
authors.forename: Yi-Sa
authors.initials: YS
authors.lastname: Huang
authors.affiliation: Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, 30010 Taiwan, R.O.C.
authors.forename: Yi-Cheng
authors.initials: YC
authors.lastname: Chu
authors.affiliation: Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, 30010 Taiwan, R.O.C.
authors.forename: Chih
authors.initials: C
authors.lastname: Chen
authors.affiliation: Department of Electronics Engineering, National Chiao Tung University, Hsinchu, 30010 Taiwan, R.O.C.
authors.forename: Dian-Rong
authors.initials: DR
authors.lastname: Lyu
authors.affiliation: Department of Electronics Engineering, National Chiao Tung University, Hsinchu, 30010 Taiwan, R.O.C.
authors.forename: Kuan-Neng
authors.initials: KN
authors.lastname: Chen
authors.affiliation: Department of Materials Science and Engineering, University of California at Los Angeles, Los Angeles, CA, 90095, U.S.A.
authors.forename: King-Ning
authors.initials: KN
authors.lastname: Tu