Low-resistance and high-strength copper direct bonding in no-vacuum ambient using highly (111)-oriented nano-twinned copper

Jing Ye Juang, Kai Cheng Shie, Po Ning Hsu, Yu Jin Li, K. N. Tu, Chih Chen

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

3 Scopus citations

Abstract

In this study, we fabricated (111)-oriented nt-Cu microbumps with 30 μm in diameter, and bonded them together using chip-to-chip bonding scheme in N2 ambient, without vacuum. A well bonded interface in the Cu-to-Cu joint was identified by the microstructure observation. Scanning electron microscope (SEM) images showed a void-less bonding interface within the bonded Cu joint. In addition, a die shear test was conducted. The test results revealed that the shear strength is 124 MPa, which is nearly two times higher than the SnAg solder joint (64 MPa). It indicates that the Cu joint is more robust than the SnAg joint. In addition, fracture analysis showed that the joint fractured in a ductile manner. Besides, we also performed the resistance measurement by using Kelvin probes on the bonded chip-to-chip test vehicles. The resistance is 4.12 mΩ for a single joint and its contact resistivity is 4.26 × 10-8 Ω·cm2. More than 30% resistance reduction has been confirmed as compared to the SnAg solder joint (6.32 mΩ). Moreover, we can further reduce the joint resistance by the second annealing process. The resistance can be brought down to 3.27 mΩ with a resistivity of 3.14 × 10-8 Ω·cm2. There is a nearly 50% resistance reduction The resistance for second annealed Cu joint is close the ideal bulk Cu. In summary, the chip-to-chip copper direct bonding has been successfully achieved and low resistance Cu-to-Cu joints has been realized by using (111) oriented nt-Cu in no-vacuum ambient.

Original languageEnglish
Title of host publicationProceedings - IEEE 69th Electronic Components and Technology Conference, ECTC 2019
PublisherInstitute of Electrical and Electronics Engineers Inc.
Pages642-647
Number of pages6
ISBN (Electronic)9781728114989
DOIs
StatePublished - 1 May 2019
Event69th IEEE Electronic Components and Technology Conference, ECTC 2019 - Las Vegas, United States
Duration: 28 May 201931 May 2019

Publication series

NameProceedings - Electronic Components and Technology Conference
Volume2019-May
ISSN (Print)0569-5503

Conference

Conference69th IEEE Electronic Components and Technology Conference, ECTC 2019
CountryUnited States
CityLas Vegas
Period28/05/1931/05/19

Keywords

  • Cu joint resistance
  • Cu-to-Cu direct bonding
  • Fracture modes
  • Grain growth
  • Nanotwinned Cu
  • Shear strength
  • Surface diffusion creep

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