Effect of Capped Cu Layer on Protrusion Behaviors of Through Silicon via Copper (TSV-Cu) Under Double Annealing Conditions: Comparative Study

Annealing process is generally adopted to reduce the residual stress and stabilize the microstructure of TSV-Cu in IC manufacturing. In this paper, the effects of capped Cu layer on the protrusion behaviors of TSV-Cu are investigated considering various double annealing processes. Higher protrusions of TSV-Cu with capped Cu layer are observed compared with that of TSV-Cu without capped Cu layer. The reason is that capped Cu layer impedes the elimination of grain boundaries and local misorientation during the first annealing, resulting in the remaining of larger amounts of atoms and higher energy in the grain boundaries. Thus, it is easier to induce protrusion by grain boundary migration during the second annealing. In addition, the capped Cu layer effects on mechanical properties of TSV-Cu under various double annealing conditions are investigated by nanoindentation test. The values of elastic modulus and hardness are generally higher in the presence of capped Cu layer. The reason is also discussed and clarified.