Phase Field Modeling of Joint Formation During Isothermal Solidification in 3DIC Micro Packaging

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In this paper, a computational multi-phase field approach is utilized to study the formation of the Cu/Sn/Cu micro-joint in 3-Dimensional Integrated Circuits (3DICs). The method considers the evolution of the system during isothermal solidification at 250 °C for the case of two different interlayer thicknesses (5 and 10 µm). The Cu/Sn/Cu interconnection structure is important for the micro packaging in the 3DIC systems. The thermodynamics and kinetics of growth of η-Cu6Sn5 and ɛ-Cu3Sn interfacial intermetallics (IMCs) are investigated by coupling the multi-phase field method with CALPHAD approach. The interaction of the phases is addressed by assuming a metastable condition for the Cu/Sn reacting system. The simulations start with the nucleation and rapid growth of the η-Cu6Sn5 IMCs at the initial stage, the nucleation and growth of ɛ-Cu3Sn IMCs at the intermediate stage ending with the full consumption of Sn layer and the domination of ɛ-Cu3Sn IMCs at the later stages. In addition, comparing different diffusion rates through the grain boundary of η phases show that their morphology is the direct consequence of balance of kinetic forces. This work provides a valuable understanding of the dominant mechanisms for mass transport in the Cu/Sn/Cu low volume interconnections. The results show that the phase field modeling is successful in addressing the morphological evolution and growth of IMC layers in the 3DIC joint formation.