Comparative evaluations on scallop-induced electric-thermo-mechanical reliability of through-silicon-vias

Sidewall scallops of through-silicon-vias (TSVs) formed during the Bosch etching process will bring serious challenges to TSV reliability. In this paper, the impact of sidewall scallops on the electric-thermo-mechanical reliability of TSVs is investigated, where the self-heating effect of TSV conductor and the residual stress caused by the deposition of different TSV layers are involved. Utilizing multi-physics field analysis with sub-modeling technique, the electric-thermo-mechanical reliability of TSVs is assessed by different indicators, including current density, temperature, heat flux and von Mises stress. It is shown that, the presence of sidewall scallops will result in periodic fluctuations in terms of current density, heat flux and stress distributions, which will further undermine TSV reliability. However, the comparative study between TSVs with polyimide liner and conventional SiO₂ liner demonstrates that, employing polyimide as TSV liner can eliminate various scallop-induced fluctuations and improve the electric-thermo-mechanical reliability of TSVs effectively.