Center for Semiconductor Technology Research
Summary Reliability of Cu-to-Cu direct bonging:
In order to realize the reliability of Cu-to-Cu direct bonding interconnects, we adopted nanotwinned Cu (nt-Cu) electroplating process to fabricate nt-Cu microbump for Cu-to-Cu direct bonding. Figure (a) is the photo of chip after bonding. Underfill (UF) dispensing was used to protect Cu microbumps. The cross-section SEM image of Cu microbump is shown in figure (b). Some chips underwent the reliability tests, including temperature cycling test (TCT) and electromigration (EM) test. To further study the failure mechanism, finite element analysis (FEA) was done to know the stress and current distribution during reliability test. This research could provide fundamental understanding for Cu-Cu joints with organic dielectric hybrid bonding.

High mechanical properties and high EM lifetime nt-Cu RDLs:
The nano-twin copper is introduced into the fan-out package line, and the excellent mechanical properties of the nano-twin copper can improve the electromigration resistance of the fan-out package line. This study found that the activation energy of the nano-twin copper line is higher than the activation energy of InFO, means that it is more resistant to electromigration. Under the same electromigration test conditions, the electromigration lifetime of nano-twin copper lines is 4 times longer than that of regular copper. This technology upgrades the strength of the copper lines by introducing a nano-twin crystal structure and uses a lithography process to make a tensile test piece with a size similar to the actual line to simulate the actual situation of the line. The research results show that the strength of nano-twin copper line is more than twice higher than that of regular copper line, although the strength is slightly reduced after annealing, elongation is significantly improved.

High Strength Nanotwinned Copper foils in Lithium Battery:
The demand for high density energy storage devices in electronic products is increasing. Lithium ion batteries, which performed an outstanding energy density, have been widely applied in electric vehicles such as products of Tesla. How to enhance the energy density of lithium ion batteries might become a big issue in the near future.For the activate material of anode is still mainly graphite. By charging lithium batteries, lithium ions will form compound with graphite and expand the anode active material. While the anode active material expands, it will squeeze onto the Cu foil. During the repeated charging-discharging process, the frequent volume change will cause the damage to the Cu foil. 5um Nanotwinned Cu we electroplated not only has the ultimate tensile strength over 780MPa, it also has good electrical resistivity almost the same with coarse-grained Cu, which makes it a potential material for current collector in lithium ion battery.

Company Description:
The center researches mayor in low-impedance internal wiring and ultra-low bump resistance technology. Especially the solder joints have been reduced to 20 microns, due to the size of microbumps continue to shrink down, the amount of solder will be less, the contact yield will decrease and the resistance will increase. This center uses (111)-oriented nano-twinned copper-copper structure to replace solder-based microbumps, and uses nano-twinned copper joints with low resistance, high heat dissipation coefficient, and anti-electromigration characteristics to solve the problem of the solder joints, which limited to its scaling ability. The following is the direction of technological development:
(A) Research on manufacture and reliability of damascene copper wire with low resistivity
(B) Research on the manufacturing and reliability of high-strength/electromigration-resistant Redistribution lines
(C) Research on manufacturing and reliability of low impedance Cu-to-Cu microbumps
Technical Film
Keyword Reliability of Cu-to-Cu direct bonging High mechanical properties and high EM lifetime nt-Cu RDLs High Strength Nanotwinned Copper foils in Lithium Battery
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