Mechanical and microstructural characterization of through-silicon via fabricated with constant current pulse-reverse modulation

Through-silicon via (TSV) copper interconnection technology is currently being developed for the next generation of electronic and microelectromechanical systems components and systems. In the present study, TSVs with different diameters from 60 to 150 µm were fabricated with constant current pulse-reverse current modulation to investigate their microstructural and mechanical properties. The mechanical characterization of these electroplated copper pillars was carried out by the nanoindentation test, which shows that the hardness of the copper deposits at the bottom is only 10% higher than at the top. The hardness of copper ranged from 1.45 to 1.8 GPa with a smaller TSV having a higher hardness. Similarly, the dependence of Young’s modulus on the diameter of the copper pillar was observed. The Young’s modulus of smaller diameter pillars was higher than that of pillars having a larger diameter. The residual stress in silicon adjacent to the dielectric layer was measured by micro-Raman spectroscopy and was about 200 MPa. The focused ion beam was used to characterize the microstructure of the electroplated copper. A significant difference in the grain size of copper along the length of TSV (∼1 to 2 µm at the bottom and ∼2 to 4 µm at the top) was revealed.