Numerical and experimental investigations on the hybrid bonding of Cu/SiÜ2 patterned surfaces using a cohesive model

Among the numerous ways to process 3D stacking of integrated circuits, a promising method is the use of Cu/SiO2 hybrid bonding, which enables simultaneous mechanical and electrical connections with an interconnection pitch limited only by photolithography resolution and alignment accuracy. In this work, we present a finite element model of the bonding of Cu/SiO2 patterned surfaces with the aim of identifying the main design and process parameters thought to affect the bonding quality, namely the pad size, shape and layout, dishing, and misalignment. We show that metal pad design induces local perturbations in the propagation of the bonding front and that the bonding quality is governed by the metal density, while pad shape, size and distribution are of little influence. This finding would allow to feed the design rules manual for hybrid bonding interconnects with drawing specifications. This analysis enables to identify the most influent factors and provide guidelines to improve bonding quality at room temperature and thereby help secure integration of 3D stacked IC products.