Feasibility Study of Nanotwinned Copper and Adhesive Hybrid Bonding for Heterogeneous Integration

In this study, the wafer-level nanotwinned copper (nt-Cu) and BCB adhesive hybrid bonding is proposed. The (111) oriented nt-Cu and BCB adhesive are used for electrical interconnection and mechanical enhancement, respectively. Nanotwinned copper direct bonding, BCB adhesive bonding, nt-Cu and BCB adhesive hybrid bonding are investigated. In nt-Cu direct bonding, the highly (111) oriented surface ratio of nt-Cu is 97% by increasing plating current density, the columnar grain size and (111) oriented surface ratio are identified by Focused Ion Beam (FIB) and Electron Back Scatter Diffraction (EBSD). The surface roughness of nt-Cu is reduced to 0.72 nm after Chemical Mechanical Polishing (CMP) and nt-Cu to nt-Cu direct bonding without large bonding voids is achieved at 250 °C for 1 h. In BCB adhesive bonding, BCB to BCB could be well bonded at 250 °C. There are no samples peeling after dicing and the average shear strength is larger than 24 MPa. Currently, the surface topography and bonding result of nt-Cu and BCB hybrid structure are improved after tuning BCB curing and fly cutting condition.