Effect of Thermal Treatment on the Mechanical Properties of Cu Specimen Fabricated Using Electrodeposition Bath for Through-Silicon-via Filling

The Cu specimens were fabricated by the UV-LIGA process using the electrodeposition bath for through-silicon-via (TSV) filling. Mechanical properties of the Cu specimens annealed at different temperatures were investigated by a uniaxial tensile test. The results indicated that the yield strength and breaking strength of as-deposited Cu specimens were higher than that of the bulk Cu, while the elastic modulus was lower than that of the bulk Cu. The elastic modulus, yield strength and breaking strength of Cu specimens decreased with the increase of the annealing temperature. When the annealing temperature was 400^oC, the elastic modulus decreased from 95 to 69GPa, the yield strength decreased from 314 to 202MPa, and the breaking strength decreased from 367 to 290MPa, respectively. In contrast, the ultimate strain increased with increasing the annealing temperature. The surface morphology, fractography and crystal structure of the Cu specimens were characterized by SEM, TEM and XRD methods. The results indicated that the particle size increased with the increase of the annealing temperature, which contributed to the decrease of the yield strength and breaking strength according to the Hall-Petch law. The XRD results indicated that as-deposited Cu specimens had a preferred orientation in (220) plane, but (311) plane became the preferred orientation with increasing the temperature. This probably contributed to the decrease of the elastic modulus with increasing the temperature.