Thermomechanical Finite Element Analysis of Cu-SiCN Hybrid Bonding with Protruding and Recessed Cu Pad in 3D-IC

Abstract Hybrid bonding is recognized as one of the most promising technologies to meet the demand of miniaturization in future three-dimensional integrated circuits (3D-IC). However, the ever-shrinking of Cu pad size poses new challenges on the yield and reliability of hybrid bonding interface. In this study, we conducted thermomechanical finite element simulations to analyze the annealing and cooling process during Cu-SiCN hybrid bonding of both protruding and recessed upper Cu structures with different Cu pad sizes, utilizing a bilinear contact model to simulate the contact at the bonding interface. The results indicate that when the Cu pad size is relatively small (0.5 μm~1.5 μm), particularly at 0.5 μm, the Cu-Cu bonding area featuring protruding Cu structure is 0.5 μm, which is 54% larger than that of 0.22 μm-recessed Cu pad structure, accompanied by a reduced thermomechanical stress by 39.81% (recessed Cu pad structure: 606.1 MPa, protruding Cu pad structure: 364.8 MPa). The results suggest that the former structure is more advantageous than the latter when the Cu pad size is less than 0.5 μm. Furthermore, we predict that the cracks are most likely to occur at the vertical Cu-SiCN sidewall. This study provides guidance for increasing the hybrid bonding area under shrunken Cu pad size conditions, and predicts the locations where interfacial cracks generate, which is promising in enhancing the yield as well as reliability of next-generation fine-pitch hybrid bonding process.