Mechanisms of copper protrusion in through-silicon-via structures at the nanoscale
journal contributionposted on 18.10.2018, 13:22 by Jinxin Liu, Zhiheng Huang, Yong Zhang, Paul Conway
Thermal stress-induced copper protrusion is frequently observed in through-silicon-vias (TSVs) based three-dimensional (3D) system integration. In this study, the detailed process of Cu protrusion is reproduced on the atomic scale using a two-mode phase-field-crystal (PFC) model, and the mechanisms of protrusion are identified. To simulate thermal loading, a “penalty term” is added to the governing equation of the PFC model. The application of loading on the TSVs induces copper grain deformation and grain boundary migration at the nanoscale. Furthermore, the simulation results suggest that the Cu protrusion is resulted from diffusional creep, involving both Nabarro-Herring creep and Coble creep. The obtained power index of diffusional creep 𝑝𝑝 is around 2.16, suggesting that lattice diffusion contributes more to protrusion than grain boundary diffusion does. The protrusion height in micron-scale TSVs predicted by extrapolating the relationship between the protrusion height and diameter of nanoscale TSVs agrees with the experimental data.
The authors acknowledge financial support from the National Natural Science Foundation of China (NSFC) under grants 51004118 and 51832002, the Pearl River Science and Technology Nova Program of Guangzhou under grant 2012J2200074, and the Guangdong Natural Science Foundation under grant 2015A030312011. Financial support from YuxiTech (Guangzhou) Limited is also gratefully acknowledged.
- Mechanical, Electrical and Manufacturing Engineering