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Hybrid bonding has been explored for more than a decade and implemented recently in high volume production at wafer-to-wafer level for image sensor applications to enable high performance chip-stacking architectures with ultra-high-density chip-to-chip interconnect. The feasibility of sub-micron hybrid bond pitch leading to ultra-high-density chip-to-chip interconnect has been demonstrated due to the elimination of solder bridging issues from microbump method. Hybrid bonding has also been actively considered for logic and memory chip-stacking, chiplets, and heterogeneous integration in general but encountering additional challenges for bonding at die-to-wafer or die-to-die level. Overlay precision, throughput, wafer dicing are among the main causes. Widening the process margin against overlay error by designing innovative hybrid bonding pad structure is highly desirable. This work proposes a method to evaluate these hybrid bonding pad structure designs and to assess the potential performance metrics by analyzing interfacial characteristics at design phase. The bonding areas and ratios of copper-copper, copper-dielectric, and dielectric-dielectric are the proposed key parameters. The correlation between bonding area ratios and overlay errors can provide insights on the sensitivity to process margins. Nonetheless, the impact of copper recess or protrusion associated with bonding area ratios are also highlighted. The proposed method is demonstrated by examining and analyzing the hybrid bonding pad structure design concepts from a few cases reported in literatures as examples. Concerns are identified for elaboration in future designs and optimizations. |
