Copper-to-copper direct bonding on highly (111)-oriented nanotwinned copper in no-vacuum ambient

Juang, Jing Ye; Lu, Chia Ling; Chen, Kuan‐Ju; Chen, Chao Chang A.; Hsu, Po Ning; Chen, Chih; Tu, King‐Ning

doi:10.1038/s41598-018-32280-x

Cited by 72 publications

(42 citation statements)

References 24 publications

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“…The distribution of grains is also presented in the enlarged images of the bonding interfaces (blue squares in Figure 4 c,d). Some triple junctions [ 42 , 43 ] were detected (blue arrows in Figure 4 c). These triple junctions led to a zig-zag bonding interface.…”

Section: Resultsmentioning

confidence: 99%

“…Some Cu grains recrystallized, and further little grains grew at the center of the bonding interface. Several zig-zag cracks propagated along the fine grains in Figure 6 c. In contrast, the cracks are straighter in Figure 6 d because the grains did not recrystallize and grow across the weak grain boundaries to form triple junctions at the bonding interface [ 42 , 43 ]. This difference was caused by the microstructure of as-fabricated Cu–Cu bumps in Figure 4 c,d.…”

Section: Resultsmentioning

confidence: 99%

“…In our previous study [ 42 ], the cross-sectional TEM images show that some voids were located at the bonding interface. Such voids are the weak points for crack initiation during TCT.…”

Section: Resultsmentioning

confidence: 99%

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Failure Mechanisms of Cu–Cu Bumps under Thermal Cycling

Shie

Hsu

et al. 2021

Materials

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The failure mechanisms of Cu–Cu bumps under thermal cycling test (TCT) were investigated. The resistance change of Cu–Cu bumps in chip corners was less than 20% after 1000 thermal cycles. Many cracks were found at the center of the bonding interface, assumed to be a result of weak grain boundaries. Finite element analysis (FEA) was performed to simulate the stress distribution under thermal cycling. The results show that the maximum stress was located close to the Cu redistribution lines (RDLs). With the TiW adhesion layer between the Cu–Cu bumps and RDLs, the bonding strength was strong enough to sustain the thermal stress. Additionally, the middle of the Cu–Cu bumps was subjected to tension. Some triple junctions with zig-zag grain boundaries after TCT were observed. From the pre-existing tiny voids at the bonding interface, cracks might initiate and propagate along the weak bonding interface. In order to avoid such failures, a postannealing bonding process was adopted to completely eliminate the bonding interface of Cu–Cu bumps. This study delivers a deep understanding of the thermal cycling reliability of Cu–Cu hybrid joints.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Failure Mechanisms of Cu–Cu Bumps under Thermal Cycling

Shie

Hsu

et al. 2021

Materials

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“…In addition, grain growth took place across the bonding interfaces at temperatures of 300 °C/100 °C (Figure 3c). The grown grains in the pillar bump side began merging with the lower nt-Cu columnar grains in the thin film side [21]. Finally, most nt-Cu columnar grains in the lower thin film side were consumed.…”

Section: Resultsmentioning

confidence: 99%

Correlation between the Microstructures of Bonding Interfaces and the Shear Strength of Cu-to-Cu Joints Using (111)-Oriented and Nanotwinned Cu

Juang

et al. 2018

Materials

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Highly (111)-oriented Cu pillar-bumps were bonded to highly (111)-oriented Cu films at temperatures ranging from 200 °C/100 °C to 350 °C/100 °C in N2 ambient conditions. The microstructures of the bonded interfaces affected the shear strength performance of the bonded Cu joints. The bonded interfaces at 300 °C/100 °C and 350 °C/100 °C had far fewer voids than interfaces bonded at 200 °C/100 °C and 250 °C/100 °C. In addition, grain growth took place across the bonding interfaces at temperatures above 300 °C/100 °C. The corresponding orientation map (OIM) showed the preferred orientation of large grown grains to be <100>. Shear tests revealed that the fracture mode was brittle for joints bonded at 200 °C/100 °C, but became ductile after bonded above 300 °C/100 °C. Based on the results, we found that voids and grain growth behavior play import roles in the shear strength performance of bonded Cu joints.

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“…Much research on low temperature Cu-to-Cu bonding has been reported [4][5][6][7][8][9][10][11][12][13][14]. The research includes coverage of surface activated bonding [4], passivation using a self-assembled monolayer [5], wet cleaning [6,7], metal passivation with Pd, Mg, Ag, or Au [8][9][10][11], Cu (111) crystal plane studies [12], Cu/SiO 2 hybrid bonding [3,13], and Cu/polymer hybrid bonding [14]. So far, the direct bonding interconnect (DBI) technique by Ziptronix [13] has been considered the most adoptable Cu bonding process in mass production.…”

Section: Introductionmentioning

confidence: 99%

Two-Step Plasma Treatment on Sputtered and Electroplated Cu Surfaces for Cu-To-Cu Bonding Application

2019

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The technology trends of next generation electronic packaging are moving toward heterogeneous 3D packaging systems. One of the key processes of 3D packaging system is Cu-to-Cu bonding, which is highly dependent on the planarized, activated, and oxygen-free Cu surface. A two-step plasma treatment is studied to form a Cu surface that does not react with oxygen and improves the Cu bonding interface quality at low bonding temperature (300 °C). In this study, the effects of two-step plasma treatment on both sputtered and electroplated Cu surfaces were evaluated through structural, chemical, and electrical analysis. The Cu bonding interface was studied by scanning acoustic tomography analysis after the thermocompression bonding process. Both sputtered and electroplated Cu thin films had the preferred orientation of (111) plane, but sputtered Cu exhibited larger grains than the electroplated Cu. As a result, the roughness of sputtered Cu was lower, and the resistivity was higher than that of electroplated Cu. Based on X-ray photoelectron spectroscopy analysis, the sputtered Cu formed more copper nitrides and fewer copper oxides than the electroplated Cu. A significant improvement in bonding quality at the Cu bonded interface was observed in sputtered Cu.

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Copper-to-copper direct bonding on highly (111)-oriented nanotwinned copper in no-vacuum ambient

Cited by 72 publications

References 24 publications

Failure Mechanisms of Cu–Cu Bumps under Thermal Cycling

Failure Mechanisms of Cu–Cu Bumps under Thermal Cycling

Correlation between the Microstructures of Bonding Interfaces and the Shear Strength of Cu-to-Cu Joints Using (111)-Oriented and Nanotwinned Cu

Two-Step Plasma Treatment on Sputtered and Electroplated Cu Surfaces for Cu-To-Cu Bonding Application

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