Experimental and Numerical Investigation of Mechanical Properties of Electroplating Copper Filled in Through Silicon Vias

Mechanical properties of electroplating copper (Cu) filled in the through silicon vias (TSVs) are critically important in the reliability assessment of TSV packages. In order to obtain its mechanical properties, such as Young's modulus, hardness, and stress-strain relationship, wafers with TSVs are fabricated by a typical manufacturing process, and then nanoindentation tests are conducted to extract Young's modulus and the hardness of TSV-Cu. The 3-D finite-element method simulations of the nanoindentation tests are conducted to determine the power law stress-strain relationship of the TSV-Cu by an iteration algorithm in which the simulated maximum nanoindentation force is compared with that by tests. Finally, Young's modulus and the hardness of the TSV-Cu obtained are 155.47 and 2.47 GPa, respectively. In addition, the power law stress-strain relationship of the TSV-Cu is presented, in which the strain hardening exponent is 0.4892 and the yield stress is 47.91 MPa. This constitutive relationship can be used to compute stress, strain, and deformation in TSV packages.