Study of Cu Pad Expansion with Surrounding Dielectrics for Hybrid Bonding

Copper/dielectric hybrid bonding technology is a key enabler for advanced chip-level (chip-to-chip, chip-to-wafer) or wafer-level (wafer-to-wafer) heterogeneous integration. In hybrid bonding, the initial room temperature bonding among the activated dielectrics is followed by Cu-to-Cu bonding at high-temperature anneal. The new dielectric materials are in the pathway toward lowering the thermal budget of the bonding process. In such an aspect, the Cu dishing could be controlled based on Cu thermal expansion. The annealing temperature is defined at which the thermal expansion of Cu should be greater than the dishing, that resulted from the damascene process. In this regard, the effect of the surrounding dielectric material around the Cu and the expansion of Cu over the applied thermal cycle need to be understood. This study focuses on the dependency of the Cu expansion with various surrounded dielectric, metal pad pitch, and its shapes, using the Finite Elemental Analysis (FEA) method with Ansys mechanical.