Effect of Annealing-Induced Tensions on the Mechanical Failure of Copper/Copper Interface in Wafer-to-Wafer Hybrid Bonding

Abstract

The copper/copper (Cu/Cu) interface has an important role in wafer-to-wafer hybrid bonding for 3D integration applications. Reports indicate the possibility of the formation of post-bonding interfacial voids and cracks which must be avoided. Here, we use molecular dynamics simulations to investigate the effect of annealing-induced tensions on the strength and deformation mechanisms of Cu/Cu interfaces. We perform tensile tests on the pristine and defective Cu/Cu interfaces including a prototypical interfacial grain boundary in two defective limits: the presence of a single (isolated) void, and an array of multiple voids. The latter resembles interfacial nanoscale roughness as a result of weak sample preparation and bonding conditions. We show that in the limit of isolated voids, the strength of the system is lower than that of the pristine interface. The corresponding deformation mechanism is ductile and through dislocation activities which could be accompanied by void growth. In contrast, multiple interfacial voids lead to a ductile-to-brittle transition in the failure mechanism accompanied by a drastic reduction of the system strength. Our findings shed light on the importance of process control to assure the integrity and reliability of the bonded components.