Surface protrusion induced by inter-diffusion on Cu-Sn micro-pillars

Yang Chen, Wenjie Dai, Yingxia Liu, Chih Chen, K.N. Tu*, Guang Chen*

*Corresponding author for this work

Research output: Journal Publications and ReviewsRGC 21 - Publication in refereed journalpeer-review

4 Citations (Scopus)
61 Downloads (CityUHK Scholars)

Abstract

With downward scaling of the micro-bumps in three-dimensional integrated circuits, surface inter-diffusion becomes dominant, changing the kinetic path of intermetallic compounds (IMC) formation and causing serious reliability issues. However, an in-depth understanding of the surface inter-diffusion process and the corresponding influence on the formation mechanism of IMC in a micro-bump remain unclear. We conducted annealing at 170 ℃, over 16 h for pillar type Sn/Cu micro-bumps and observed a unique 2-step sidewall Cu3Sn IMC formation phenomenon on the FIB-cut clean surface of the micro-bumps. It is found the two-step sidewall IMC formation is dominated by the surface inter-diffusion of Sn and Cu atoms. Density functional theory calculations reveal that the activation energy barrier of nucleation for sidewall Cu3Sn IMC is about 1/3 of that of sidewall Cu6Sn5 on corresponding interfacial IMC layers, making the formation of sidewall Cu3Sn dominant. Moreover, we proposed a kinetic model that can predict the mean lateral growth rate of the sidewall IMC which may cause fatal short-circuit failure. © 2022 The Author(s). Published by Elsevier Ltd. 
Original languageEnglish
Article number111318
JournalMaterials & Design
Volume224
Online published27 Oct 2022
DOIs
Publication statusPublished - Dec 2022
Externally publishedYes

Research Keywords

  • Surface inter-diffusion
  • Intermetallic compounds (IMCs)
  • 3D IC
  • Nucleation

Publisher's Copyright Statement

  • This full text is made available under CC-BY-NC-ND 4.0. https://creativecommons.org/licenses/by-nc-nd/4.0/

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