Effect of annealing on the toughness of 40-μm-wide nanotwinned Cu lines

This study investigates the toughness of 40-μm-wide nanotwinned Cu lines before and after annealing. The toughness of Cu lines was measured by tensile test, and different annealing temperatures and durations were used to examine the thermal stability of the nt-Cu films. The initial and post-annealed microstructures was analyzed, and initial surface orientation of Cu lines was examined. The tensile test results showed the mechanical properties of nt-Cu lines is better than that of regular Cu lines. In addition, the toughness of nt-Cu lines significantly increased after annealing, although the ultimate tensile strength slightly dropped. The nanotwinned Cu is very suitable For application as redistribution lines in Fan-Out Wafer-Level Packaging (FO-WLP), because the toughness of nt-Cu lines increased after the annealing at 250°C for 3 h, which is close to the curing process of polyimide capping.