Characterization of Thermal Conductance of Copper-to-Copper Bonded Interconnects with Metal Passivation for Three-Dimensional Integration

Copper-to-Copper (Cu-to-Cu) bonding with metal passivation addresses fundamental oxidation and thermal budget in Cu-to-Cu bonding, yet thermal transport characterization remains unexplored despite critical importance for thermal management of three-dimensional integration. This study investigates the thermal conductance of Cu-to-Cu bonded interconnects with metal passivation, where quantifying the discrepancy between predicted and experimentally measured thermal transport properties in three-dimensional integrated structures enables design validation and optimization of thermal management strategies under conditions of elevated thermal density where thermal management becomes critical. We developed a time-domain thermoreflectance (TDTR) methodology employing transparent sapphire substrates to optically access the bonded layer. A tantalum (Ta) diffusion barrier is also employed to prevent aluminum-copper interdiffusion during bonding, ensuring measurement integrity. Multilayer thermal modeling incorporating comprehensive sensitivity analysis enables precise determination of the thermal conductance of localized bonded region, overcoming fundamental limitations of conventional approaches that measure bulk thermal properties across entire bonded structures. Systematic optimization of the Cu layer thickness of each side maximizes measurement sensitivity to Cu-to-Cu bonded interconnects while suppressing peripheral contributions that would otherwise compromise measurement fidelity. Comprehensive structural and material characterization via transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and selected area electron diffraction (SAED) pattern analysis revealed correlation between interfacial structure and measured thermal transport properties in metal-passivated Cu-to-Cu bonded interconnects. The measured conductance values, an order of magnitude below Wiedemann-Franz predictions from electrical resistivity data, indicate dominant electron scattering mechanisms at heterogeneous interfaces, microstructural discontinuities, and oxygen-rich regions within the bonded layer. These findings provide critical thermal management insights for 3D integrated electronic systems employing Cu-to-Cu bonding with metal passivation.