Microstructure and hardness of electrodeposited copper microcylinders in through-silicon via by direct current power

Two-step direct current electroplating was used to fabricate copper microcylinders with a 50 μm diameter and 150 μm depth. The microstructure was characterised by electron back scattering detection. Twin boundaries appeared and the twin quantity depended on the current density. Near the edge (2 mA/cm2), the grain size was large (∼2 μm) and many twins existed, while the size was small (∼0.5 μm) and few twins occurred in the middle (4 mA/cm2). The hardness was measured by nano-indentation technique. The results showed that the hardness (2.7 GPa) at the edge of the sample was higher than that in the middle (2.2 GPa), which was probably enhanced by twins. The hardness of annealed sample was about 1.7 Gpa, which was independent of the position.