Polymer Dielectric Materials Evaluation for Hybrid Bonding Applications

Hybrid bonding is an emerging technology for advanced packaging and heterogeneous integration. In this work, Cu/polymer-based hybrid bonding is being evaluated using two types of polymer materials (photo and non-photo sensitive) for low temperature hybrid bonding applications. Hybrid bonding & annealing at lower temperatures are very critical for specific device types, and it necessitate thorough characterization of low temperature curing polymers. Polymers used in this study are polyimide based and have lower curing temperatures around 200 °C. CMP process module has been established using different slurries to achieve copper protrusion for Cu/polymer features, and Cu protrusion is very critical for polymer hybrid bonding due to a huge CTE mismatch during the tacking/bonding process. Three types of copper protrusions (5nm, 10nm, and 15nm) are being evaluated to achieve robust hybrid bonding and good Cu-Cu diffusion. Extensive hybrid bonding DOE is evaluated with different pre-clean conditions, tacking temperatures & loads, and annealing conditions. AFM analysis was used to measure the roughness and dishing/protrusion profile, and after the CMP process, the surface roughness of these polymers was obtained < 1nm. Both single-chip bonding using face-to-face bonding and chip stacking hybrid bonding are being evaluated. CSAM, SEM analysis, and die shear were performed to characterize the bonding quality and eventually to down select the polymer with appropriate Cu protrusion.