Synergistically promoted direct bonding of nanotwinned copper at 200 °C viareductive solvents

Purpose This study aims to address the high-temperature bottleneck of Cu-Cu direct bonding in three dimensional (3D) heterogeneous integration (3D HI) by proposing a synergistic regulation strategy involving (111) preferred orientation nanotwinned copper [(111) nt-Cu] and 5% ascorbic acid aqueous solution. Design/methodology/approach Bonding experiments were conducted under 200 °C, 30 MPa and a vacuum of <20 Pa, with annealing time (30 and 60 min) as the variable. The interface quality was systematically investigated using characterization techniques including X-ray diffraction, electron backscatter diffraction, focused ion beam, energy-dispersive spectroscopy and mechanical tests. Findings (111) nt-Cu’s high-density twin boundaries and (111) close-packed planes enable low-resistance atomic diffusion channels, while 5% ascorbic acid efficiently removes surface oxides and suppresses re-oxidation; The 30 min annealing group retains trace organic residues at the interface, whereas 60 min annealing promotes sufficient grain bridging without obvious impurities; The 60 min group achieves a shear strength of 145.81 MPa, a 59.5% increase compared to the 30 min group (91.45 MPa). Originality/value This technology reduces the bonding thermal budget through the dual-dimensional synergy of structural regulation and chemical regulation, providing a feasible solution for high-density interconnection of temperature-sensitive devices.