Influence of Inhomogeneous Anisotropic Copper Grains in TSV on the Thermo-Mechanical Behaviors in the Annealing Process

With the rapid development of 3-D packaging technology, the thermal reliability of high-aspect-ratio through silicon via (TSV) has become an urgent problem. The inhomogeneity of TSV-Cu induced by the grain growth during annealing should not be ignored. The inhomogeneities in grain size, morphology, and mechanical property anisotropy, among others, may severely affect TSV manufacturing. In this work, the characterization experiments have been carried out by SEM and electron backscatter diffraction (EBSD) on TSV samples with an aspect ratio of 10 first; then, the copper grain was grown into morphologies by DFM, and a variety of models with different TSV-Cu grain sizes and distributions were built considering the mechanical anisotropy of Cu crystal. To explore the influence of the distribution of TSV-Cu anisotropic grains on their thermo-mechanical reliability at high temperatures and protrusion behavior after annealing, a group of annealing processes with different temperatures was simulated. The results show that TSV-Cu with larger grains in the top region has lower high-temperature thermal stress, equivalent plastic strain, and residual stress after high-temperature annealing. However, the protrusion height is only related to average grain size, and the TSV-Cu filled with large-size grain has the largest protrusion height and is more prone to failure.