Cu/Cu direct bonding by metal salt generation bonding technique with organic acid and persistence of reformed layer

Koyama, Satoshi; Hagiwara, Naoki; Shohji, Ikuo

doi:10.7567/jjap.54.030216

Cited by 8 publications

(7 citation statements)

References 29 publications

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“…The combined use of hydrazine, copper(II) acetate, and ethylene glycol were important to achieve the high-concentration synthesis of sub-10-nm Cu NPs in this synthesis. For example, large aggregates of Cu NPs were formed when we used copper(II) formate as the replacement for copper(II) acetate in the synthesis (not shown), although copper(II) formate has been often used for the synthesis of Cu NPs due to the volatile and self-reducing properties of formate anions. − Propylene glycol is well-known as a typical polyol solvent, but large aggregates of Cu NPs were formed when we used propylene glycol as the replacement for ethylene glycol in the synthesis (not shown).…”

Section: Resultsmentioning

confidence: 99%

High-Concentration Synthesis of Sub-10-nm Copper Nanoparticles for Application to Conductive Nanoinks

Hokita

Kanzaki

Sugiyama

et al. 2015

ACS Appl. Mater. Interfaces

100

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A simple, high-concentration (up to 0.6 M Cu salt) synthesis of sub-10-nm copper nanoparticles (Cu NPs) was developed in ethylene glycol at room temperature under ambient air conditions using 1-amino-2-propanol (AmIP) as the stabilizer. Monodispersed AmIP-Cu NPs of 3.5 ± 1.0 nm were synthesized in a high yield of ∼90%. Thus, nearly 1 g of sub-10-nm Cu NP powder was obtained using a one-step synthesis for the first time. It is proposed that metallacyclic coordination stability of a five-membered ring type between the Cu and AmIP causes the high binding force of Am IP onto the Cu surface, resulting in the superior stability of the AmIP-Cu NPs in a solution. The purified powder of AmIP-Cu NPs can be redispersed in alcohol-based solvents up to high Cu contents of 45 wt % for the preparation of Cu nanoink. The resistivity of the conductive Cu film obtained from the Cu nanoink was 30 μΩ cm after thermal heating at 150 °C for 15 min under a nitrogen flow. The long-term resistance stability of the Cu film under an air atmosphere was also demonstrated.

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Section: Resultsmentioning

confidence: 99%

High-Concentration Synthesis of Sub-10-nm Copper Nanoparticles for Application to Conductive Nanoinks

Hokita

Kanzaki

Sugiyama

et al. 2015

ACS Appl. Mater. Interfaces

100

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“…A dicing process was then carried out, and the samples were diced into the top (6 × 6 mm 2 ) and bottom (15 × 15 mm 2 ) dies. The bonding surfaces were cleaned with a citric acid [23,24] and DI water, and blown dry through an N 2 purge. The reason for this is that the native oxide layer on the bonding interface, acting as a barrier for atomic diffusion, may critically affect its bonding quality.…”

Section: Methodsmentioning

confidence: 99%

Shearing Characteristics of Cu-Cu Joints Fabricated by Two-Step Process Using Highly <111>-Oriented Nanotwinned Cu

Ong

Tran

Yang

et al. 2021

Metals

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Cu-Cu bonding has the potential to break through the extreme boundary of scaling down chips’ I/Os into the sub-micrometer scale. In this study, we investigated the effect of 2-step bonding on the shear strength and electrical resistance of Cu-Cu microbumps using highly <111>-oriented nanotwinned Cu (nt-Cu). Alignment and bonding were achieved at 10 s in the first step, and a post-annealing process was further conducted to enhance its bonding strength. Results show that bonding strength was enhanced by 2–3 times after a post-annealing step. We found 50% of ductile fractures among 4548 post-annealed microbumps in one chip, while the rate was less than 20% for the as-bonded counterparts. During the post-annealing, interfacial grain growth and recrystallization occurred, and the bonding interface was eliminated. Ductile fracture in the form of zig-zag grain boundary was found at the original bonding interface, thus resulting in an increase in bonding strength of the microbumps.

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“…For example, it was found that by modifying the Cu/Sn bonding surface with formic acid, it was possible to fabricate a base metalbreaking joint in Sn at a bonding temperature as low as 40 K. 12) It was found that by modifying the Cu bonding surface with formic acid or citric acid, it was possible to fabricate joints with the same bonding strength as those without treatment, even at a 150 K lower bonding temperature. 13) It was found that the modification treatment using formic acid on the bonding surface of SUS304 stainless steel improved the bonding strength to about twice that of the case where no treatment was applied. 14) It was found that the bonding strength was greatly improved by inserting a highpurity Al sheet with a formate film at the bonding interface between pure Ti.…”

Section: Introductionmentioning

confidence: 98%

“…However, it has been pointed out that an oxide film and a processed layer exist on the actual bonding surface, and these inhibit solid-state bonding. 13) Therefore, in order to form a connection portion having high bonding strength, it is necessary to remove the oxide film on the bonding surface. Therefore, a method for removing a surface oxide film using ultrasonic vibration 47) or a plasma processing 811) has been studied.…”

Section: Introductionmentioning

confidence: 99%

Low Temperature Solid-State Bonding of Nickel and Tin with Formic Acid Surface Modifications

2022

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The effect of formic acid surface modification process on the bond strength of the solid-state bonded interface of tin and nickel was investigated by SEM observations of fractured surfaces and interfacial microstructures. Tin and nickel surfaces were modified by boiling in formic acid for 600 s. Diffusion bonding was performed at bonding temperatures of 393493 K under a load of 7 MPa (bonding time for 1.8 ks). The bond strength increased with increasing bonding temperature irrespective of surface modification process. As a result of surface modification process, bonded joints were obtained at a bonding temperature 70 K lower than that required for non-modified surfaces used, and the bond strength was comparable to that of the base metal. When the surface modification process was not applied, the fracture mode was brittle. As the bond strength increased with increasing bonding temperature, the fracture mode changed to ductile. With surface modification process, this tendency was observed at a bonding temperature 70 K lower than without it. The results suggest that these changes in the fractured surface between tin and nickel were accompanied by expansion of the metal-to-metal contact area, which contributed to the increase in bond strength.

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Cu/Cu direct bonding by metal salt generation bonding technique with organic acid and persistence of reformed layer

Cited by 8 publications

References 29 publications

High-Concentration Synthesis of Sub-10-nm Copper Nanoparticles for Application to Conductive Nanoinks

High-Concentration Synthesis of Sub-10-nm Copper Nanoparticles for Application to Conductive Nanoinks

Shearing Characteristics of Cu-Cu Joints Fabricated by Two-Step Process Using Highly <111>-Oriented Nanotwinned Cu

Low Temperature Solid-State Bonding of Nickel and Tin with Formic Acid Surface Modifications

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