A Microstructural Investigation of Sub-1 μm Copper Bonding Contact Structures in Die-to-Wafer Hybrid Bonding

This study explored the fine pitch scalability of the die-to-die level vertical stacking through the Cu/SiO
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hybrid bonding technique for chips with varying Cu contact diameters (0.8-4 μm) and pitch spacings (2-10 μm). It also addresses challenges associated with the scalability of hybrid bonding including the precise alignment of the top/bottom Cu pads. In addition, we seek a better understanding of the microstructural evolution and mechanical deformation of Cu grains during the hybrid bonding process. This involves microstructural characterization of the Cu films before and after the hybrid bonding via scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). In conclusion, this study offers some explanation on controlling mechanisms of the Cu-Cu bonding and highlights the desirable initial microstructural features and grain orientations of the Cu pads to improve the Cu-Cu bonding quality for hybrid bonding.