Electronic Materials Letters

The Korean Institute of Metals and Materials (대한금속재료학회)
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Direct, CMOS In-Line Process Flow Compatible, Sub 100℃ Cu-Cu Thermocompression Bonding Using Stress Engineering

  • Panigrahi, Asisa Kumar (Department of Electrical Engineering, Indian Institute of Technology Hyderabad) ;
  • Ghosh, Tamal (Department of Electrical Engineering, Indian Institute of Technology Hyderabad) ;
  • Kumar, C. Hemanth (Department of Electrical Engineering, Indian Institute of Technology Hyderabad) ;
  • Singh, Shiv Govind (Department of Electrical Engineering, Indian Institute of Technology Hyderabad) ;
  • Vanjari, Siva Rama Krishna (Department of Electrical Engineering, Indian Institute of Technology Hyderabad)
  • Received : 2017.08.30
  • Accepted : 2018.01.04
  • Published : 2018.05.31
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Abstract

Diffusion of atoms across the boundary between two bonding layers is the key for achieving excellent thermocompression Wafer on Wafer bonding. In this paper, we demonstrate a novel mechanism to increase the diffusion across the bonding interface and also shows the CMOS in-line process flow compatible Sub $100^{\circ}C$ Cu-Cu bonding which is devoid of Cu surface treatment prior to bonding. The stress in sputtered Cu thin films was engineered by adjusting the Argon in-let pressure in such a way that one film had a compressive stress while the other film had tensile stress. Due to this stress gradient, a nominal pressure (2 kN) and temperature ($75^{\circ}C$) was enough to achieve a good quality thermocompression bonding having a bond strength of 149 MPa and very low specific contact resistance of $1.5{\times}10^{-8}{\Omega}-cm^2$. These excellent mechanical and electrical properties are resultant of a high quality Cu-Cu bonding having grain growth between the Cu films across the boundary and extended throughout the bonded region as revealed by Cross-sectional Transmission Electron Microscopy. In addition, reliability assessment of Cu-Cu bonding with stress engineering was demonstrated using multiple current stressing and temperature cycling test, suggests excellent reliable bonding without electrical performance degradation.

Keywords

References

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