Compensation of Surface Roughness Using an Au Intermediate Layer in a Cu Direct Bonding Process

Hirokazu Noma*, Takumi Kamibayashi, Hiroyuki Kuwae, Naoya Suzuki, Toshihisa Nonaka, Shuichi Shoji, Jun Mizuno

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)


Copper-copper (Cu-Cu) direct bonding assisted by direct immersion gold (DIG) was demonstrated. Cu-Cu direct bonding is a critical technology for inductively coupled memory interconnections. To solve the problems of conventional methods of Cu-Cu direct bonding, a plating process using DIG to form an intermediate layer was selected. The concept of the developed bonding process is to use deformation of DIG to compensate for the surface roughness of the Cu substrates during application of pressure and annealing. Using this method, precise surface flattening of Cu substrates is not necessary. Bonding can be achieved even in an air atmosphere. A sample bonded at a temperature of 350°C failed within the chip in a shear test. It was found that bonding can be achieved when the gold (Au) thickness is greater than the half of the surface roughness of Cu at the bonding temperature. Transmission electron microscopy-energy-dispersive x-ray spectroscopy revealed that Au diffused into Cu during bonding. The diffusion constant of Au into Cu was investigated through a numerical calculation. The obtained results showed good agreement with the literature values.

Original languageEnglish
Pages (from-to)5403-5409
Number of pages7
JournalJournal of Electronic Materials
Issue number9
Publication statusPublished - 2018 Sept 1


  • Au-Cu alloy
  • Direct immersion gold
  • copper direct bonding
  • magnetic coupling
  • memory package
  • three-dimensional interconnection

ASJC Scopus subject areas

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


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