Figure 4

Variation in grain growth phenomena with bonding time for a temperature gradient between 450 °C at the top die and 100 °C at the bottom die: (a) 5 min; the nt-Cu in the bump has transformed to randomly oriented large grains, (b) 10 min; grain growth occurred through some of the large grains into the nt-Cu in the thin film, and (c) 15 min; grain growth with annealing twins occurred in most of the thin film. The areas corresponding to the dashed rectangular boxes in (a) to (c) are enlarged in the right-hand side images.