Failure Mechanisms of Cu–Cu Bumps under Thermal Cycling

Shie, Kai-Cheng; Hsu, Po Ning; Li, Yu Jin; Tran, Dinh-Phuc; Chen, Chih

doi:10.3390/ma14195522

Cited by 30 publications

(11 citation statements)

References 50 publications

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“…The schematic diagram of fabrication processes is shown in Figure 2 . Detailed processes can be referred to in our previous study [ 12 ]. The cross-sections of the joints were then characterized using focused ion beam (DB-FIB, Field Electron and Ion Company, Hillsboro, OR, USA), and the surface roughness ( R q ) was examined by an atomic force microscope (AFM, Bruker Dimension Edge and Dimension Icon, Bruker Company, Billerica, MA, USA).…”

Section: Experimental and Simulation Sectionmentioning

confidence: 99%

“…Although <111> crystal orientation is beneficial for direct bonding, a relatively high density of voids at the center of the bonding interface was still observed after a temperature cycling test without an applied force [ 12 ]. Various voids originally exist at metal surfaces and then move along grain boundaries to the center of the bonding interface due to stress gradients [ 13 , 14 , 15 ].…”

Section: Introductionmentioning

confidence: 99%

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Failures of Cu-Cu Joints under Temperature Cycling Tests

et al. 2022

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In this study, the failure mechanisms of Cu-Cu joints under thermal cycling were investigated. Two structures of dielectrics (PBO/underfill/PBO and SiO2) were employed to seal the joints. Stress gradients induced in the joints with the different dielectrics were simulated using a finite element method (FEM) and correlated with experimental observations. We found that interfacial voids were forced to move in the direction from high stress regions to low stress ones. The locations of migrated voids varied with the dielectric structures. Under thermal cycling, such voids were likely to move forward to the regions with a small stress change. They relocated and merged with their neighboring voids to lower the interfacial energy.

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Section: Experimental and Simulation Sectionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Failures of Cu-Cu Joints under Temperature Cycling Tests

et al. 2022

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“…In the semiconductor industry, copper (Cu) is considered as the most commonly used interconnect for fan-out wafer level packaging thanks to its superior electrical and thermal conductivity [ 1 , 2 , 3 , 4 , 5 , 6 ]. In order to enhance the computing performance of electronic devices, logic chips and interconnects are required to scale down significantly [ 7 , 8 , 9 ]. During operation, Cu lines are subjected to a high current density resulting in severe failures related to electromigration (EM), stress migration, and Joule heating [ 10 , 11 , 12 ].…”

Section: Introductionmentioning

confidence: 99%

Stress Relaxation and Grain Growth Behaviors of (111)-Preferred Nanotwinned Copper during Annealing

et al. 2023

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Highly (111)-oriented nanotwinned Cu (nt-Cu) films were fabricated on silicon wafers for thermal-stress characterization. We tailored the microstructural features (grain scale and orientation) of the films by tuning the electroplating parameters. The films were heat-treated and the relaxation behaviors of thermal stresses in the films were explored using a bending beam system. Focused ion beam (FIB) and electron back-scattered diffraction (EBSD) were then employed to characterize the transformations of the microstructure, grain size, and orientation degree of the films. The results indicated that the degree of (111)-preferred orientation and grain size significantly decrease with increasing the current density. The nt-Cu films with a higher degree of (111)-preferred orientation and larger grains exhibit the slower rates of stress relaxation. The film with larger grains possesses a smaller grain boundary area; thus, the grain boundary diffusion for the thermal-stress release is suppressed. In addition, the induced tensile stress in the films with larger grains is smaller leading to the difference in microstructural changes under annealing.

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“…The sample for the EM test is shown in Figure 1. A top die was bon die through instant Cu-Cu direct bonding [18,31]. The method of electr winned Cu (nt-Cu) [32,33] was adopted to fabricate nt-Cu microbumps be lumnar grains have a (111) surface for low-thermal-budget bonding [15 chanical properties [34][35][36][37].…”

Section: Introductionmentioning

confidence: 99%

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

Shie

Hsu

et al. 2021

Materials

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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.

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Failure Mechanisms of Cu–Cu Bumps under Thermal Cycling

Cited by 30 publications

References 50 publications

Failures of Cu-Cu Joints under Temperature Cycling Tests

Failures of Cu-Cu Joints under Temperature Cycling Tests

Stress Relaxation and Grain Growth Behaviors of (111)-Preferred Nanotwinned Copper during Annealing

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

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