Analysis of Bonding Interfaces of Pressureless-sintered Cu on Metallization Layers

D Ishikawa and BN An and M Mail and H Wurst and B Leyrer and T Blank and M Weber and S Ueda and H Nakako and Y Kawana, 2019 INTERNATIONAL CONFERENCE ON ELECTRONICS PACKAGING (ICEP 2019), 167-172 (2019).

this paper describes thermal stabilities (573 K for 8 h) of pressureless-sintered Copper (Cu) on four kinds of top metallization layers (Ni, Cu, Ag, and Au) by experiments. Evolutions of sintering process of Cu nanoparticles and diffusion coefficients of interfaces between a bulk Cu layer and metallization layers were also evaluated by molecular dynamics (MD) simulations. After aging at 573 K for 8 h in terms of bonding samples, the shear strengths of sintered Cu on Ni and Cu layer increased, whereas those of sintered Cu on Ag and Au layer decreased. It was confirmed that interdiffusion occurred in the interfaces between sintered Cu layer and Ag layer or Au layer by energy dispersive X-ray spectroscopy (EDX), which increased the porosities of sintered Cu near the interfaces. The increases of interfacial porosities on sintered Cu/Ag and sintered Cu/Au decreased the shear strengths. In contrast, the porosities near the interface between sintered Cu layer and Ni layer or Cu layer hardly changed after aging. MD simulations revealed that Kirkendall voids were promoted by higher interdiffusion coefficients and higher ratio of intrinsic diffusion coefficients between a bulk Cu layer and metallization layers, which consequently increased the porosities of sintered Cu near the interfaces. The interdiffusion coefficients, which seem to have a correlation with the shear strengths of sintered Cu, can be used as an index value to find metallization layers that are suitable for the sintered Cu layer by calculations of MD simulations.

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