Effect of Bonding Strength on Electromigration Failure in Cu–Cu Bumps

In microelectronic packaging technology for three-dimensional integrated circuits (3D ICs), Cu-to-Cu direct bonding appears to be the solution to solve the problems of Joule heating and electromigration (EM) in solder microbumps under 10 μm in diameter. However, EM will occur in Cu–Cu bumps when the...

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Bibliographic Details
Published in:Materials 2021-10, Vol.14 (21), p.6394
Main Authors: Shie, Kai-Cheng, Hsu, Po-Ning, Li, Yu-Jin, Tu, K. N., Chen, Chih
Format: Article
Language:English
Subjects:
Bonding strength
Circuits
Current density
Cu–Cu direct bonding
Diameters
Diffusion layers
Electromigration
Electronic packaging
Failure
Grain boundaries
Grain growth
Integrated circuits
Interfaces
Ohmic dissipation
Passivity
Resistance heating
Thermal mismatch
three-dimensional integrated circuits (3D ICs)
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Summary:In microelectronic packaging technology for three-dimensional integrated circuits (3D ICs), Cu-to-Cu direct bonding appears to be the solution to solve the problems of Joule heating and electromigration (EM) in solder microbumps under 10 μm in diameter. However, EM will occur in Cu–Cu bumps when the current density is over 106 A/cm2. The surface, grain boundary, and the interface between the Cu and TiW adhesion layer are the three major diffusion paths in EM tests, and which one may lead to early failure is of interest. This study showed that bonding strength affects the outcome. First, if the bonding strength is not strong enough to sustain the thermal mismatch of materials during EM tests, the bonding interface will fracture and lead to an open circuit of early failure. Second, if the bonding strength can sustain the bonding structure, voids will form at the passivation contact area between the Cu–Cu bump and redistribution layer (RDL) due to current crowding. When the void grows along the passivation interface and separates the Cu–Cu bump and RDL, an open circuit can occur, especially when the current density and temperature are severe. Third, under excellent bonding, when the voids at the contact area between the Cu–Cu bump and RDL do not merge together, the EM lifetime can be more than 5000 h.
ISSN:1996-1944
1996-1944
DOI:10.3390/ma14216394