Low-Temperature (70°C) Cu-to-Cu Direct Bonding by Capping Metal Layers

Demin Liu, Po Chih Chen, Yu Wei Liu, Han Wen Hu, Kuan Neng Chen*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

10 Scopus citations


Cu-Cu direct bonding at low temperature with Cr wetting layer and Au passivation has been developed, and the bonding mechanism has been investigated. A chip-level Cu-to-Cu direct bonding can be achieved under a very low thermal budget condition at 70 °C for 90 s or 150 °C for 15 s, while wafer level bonding can be achieved at 100 °C under a low vacuum environment (10{-{2}} Torr) by deposition of capping metal layers, which can protect Cu from oxidation, as well as reduce surface roughness and grain size of Cu. During the bonding process, Cu atoms diffuse through Cr/Au layers into the bonding interface, forming a new inter-layer without voids to achieve high quality bonding. The phenomenon of recrystallization and effects of grain size have been validated by TEM analyses. This Cu-Cu bonding with capping metal layers scheme can enable bonding with ultra-low thermal budget, excellent bonding quality, good electrical performance and high reliability, showing the great feasibility for the 3D integration applications.

Original languageEnglish
Pages (from-to)1524-1527
Number of pages4
JournalIeee Electron Device Letters
Issue number10
StatePublished - Oct 2021


  • 3D integration
  • Cu bonding
  • metal passivation


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