Modeling of Stress-Driven Void Evolution at the Cu-Cu Hybrid Bonding Interface

초록

Voids formed during the hybrid bonding process not only degrade electrical properties but also serve as initiation sites for electromigration-induced failures. Therefore, a quantitative method capable of predicting and analyzing interfacial voids is required. In this study, a finite element method (FEM) framework coupled with a creep model and a stress-driven migration model is developed to analyze the mechanism of void evolution at the hybrid bonding interface. In particular, the simulation investigates stress-driven mass transport along the hydrostatic stress gradient induced by the initial Cu surface roughness and thermomechanical loads. The proposed model is validated by quantitatively comparing simulation results with the interfacial voids observed in experimental hybrid bonding samples. For the largest measured void, the predicted diameter and volume are within 7.2% (diameter) and 12.7% (volume) error, respectively, and the predicted average void area fraction agrees with an absolute error of 0.006 percentage points. Parametric studies further quantify the dependencies of void growth on the initial Cu pad surface roughness and annealing conditions, providing practical process guidelines to mitigate interfacial voiding.

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