Effect of Process and Design Parameters in Cu/SiCN Hybrid Bonding Process: A Finite Element Analysis Study

There is a critical need to understand the optimal process conditions and pad design for hybrid bonding at progressively finer pitches. The finite element method (FEM) analysis is a valuable approach for elucidating the bonding mechanism and predicting the bonded area. In this study, we investigated hybrid bonding using FEM analysis to study bonding mechanisms and suggest optimal design strategies. Models were constructed for sub-micrometer copper pads with silicon carbonitride (SiCN) as the dielectric film at the bonding interface, with variations in copper pad dimensions and dishing depth. The postbond annealing process was simulated with different annealing temperatures. The results show that high annealing temperatures and low chemical mechanical polishing (CMP) dishing depths promote sufficient pad expansion to achieve complete copper-to-copper bonding, which is consistent with established observations in the field. Furthermore, the study highlights a strong dependence of the bonded area on the copper pad dimensions, emphasizing the need for proper optimization of pad dimensions. In particular, copper bonding was highly sensitive to pad thickness and aspect ratio. As the pad thickness increased, thermal expansion increased, resulting in a larger bonded area. For all pad thicknesses, maximum thermal expansion occurred at an aspect ratio of approximately 0.4. Therefore, a specific diameter range was identified where the maximum bonded area could be achieved for a given pad thickness.