Interfacial reactions in Cu/Ga and Cu/Ga/Cu couples

Shih Kang Lin, Cheng Liang Cho, Hao Miao Chang

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41 Citations (Scopus)


Cu-to-Cu bonding to connect through-silicon vias in three-dimensional integrated-circuit packaging is the most important interconnection technology in the next-generation semiconductor industry. Soldering is an economic and fast process in comparison with diffusion bonding methods. Ga has high solubility of up to 20 at.% in the Cu-rich face-centered cubic (FCC) phase and high mobility at moderate temperatures. In this work, an attempt has been made to evaluate Ga-based Cu-to-Cu interconnection by transient liquid-phase (TLP) bonding. The Cu/Ga interfacial reactions at temperatures ranging from 160 C to 300 C were examined. For reactions at temperatures lower than 240 C, the reaction path is Cu/γ 3-Cu9Ga4/θ-CuGa 2/liquid, where the γ 3-Cu9Ga4 and θ-CuGa2 phases are thin planar and thick scalloped layers, respectively, while for the reactions at 280 C and 300 C, the scalloped γ 3-Cu9Ga4 phase is the only reaction product. The phase transformation kinetics, reaction mechanisms, and microstructural evolution in the Cu/Ga couples are elaborated. In addition, reactions of Cu/Ga/Cu sandwich couples at 160 C were investigated. The original Cu/liquid/Cu couples isothermally transformed to Cu/γ 3-Cu 9Ga4/ θ-CuGa23-Cu9Ga4/Cu couples as the reaction progressed. However, cracks were observed in the θ-CuGa2 phase regions after metallographic processing. The brittle θ-CuGa2 phase is undesirable for Ga-based TLP bonding.

Original languageEnglish
Pages (from-to)204-211
Number of pages8
JournalJournal of Electronic Materials
Issue number1
Publication statusPublished - 2014 Jan

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Electrical and Electronic Engineering
  • Materials Chemistry


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