Low-temperature and low-pressure direct copper-to-copper bonding by highly (111)-oriented nanotwinned Cu

Chen, Chih; Liu, Chien-Min; Lin, Hung-Wen; Huang, Yi-Sa; Chu, Yi‐Cheng; Lyu, Dian-Rong; Chen, Kuan‐Neng; Tu, King‐Ning

doi:10.1109/panpacific.2016.7428434

Cited by 11 publications

(6 citation statements)

References 31 publications

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“…Ductile fracture of 4548 microbumps in a chip equaled as 1%, as shown in Table 4. It has been reported that some nt-Cu columnar grains grew into larger grains, and shifted to other orientations under a high bonding temperature [7][8][9]. This was conducted under 40 MPa for 20 min.…”

Section: Resultsmentioning

confidence: 99%

“…Excellent reliability, small size, high functionality, and low-cost of devices are thus required. However, it is incredibly difficult to shrink down the pitch of solder microbumps below 10 µm [1][2][3][4][5][6][7][8], due to bridging and the side wall wetting effect [9][10][11]. Cu-Cu bonding has shown potential in overcoming the limitation of scaling down into the sub-micron scale, and impede the delay problem of RC signal.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

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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“…Highly (111)-nanotwinned Cu (nt-Cu) pillar bumps and films were fabricated to facilitate the Cu-to-Cu direct bonding. It has been reported that the (111) plane of Cu possesses a high surface diffusivity, so the unidirectionally-oriented (111)-nanotwinned Cu enables low temperature direct bonding via surface creep [17,18,19]. The electrodeposition procedures used for the (111) nt-Cu were reported in our previous publication [20].…”

Section: Methodsmentioning

confidence: 99%

“…The microstructure bonding interfaces were then analyzed. The novelty of this study is that we adopted highly (111)-oriented nanotwinned Cu (nt-Cu) and take advantages of its high surface diffusivity [17,18,19]. Therefore, the Cu direct bonding can be achieved at no-vacuum ambient conditions.…”

Section: Introductionmentioning

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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“…Nanotwinned copper has been reported to 2 have distinctive properties, such as high surface diffusivity and good mechanical and electrical properties [10][11][12][13][14]. Chen et al has reported that low-temperature (150°C) and low-pressure (114 psi) Cu-Cu direct bonding can be performed in ordinary vacuum by using (111)-oriented nt-Cu films obtained by electroplating [15]. The reason is that Cu has a face-centred cubic structure, and (111), the closest packed plane, possesses the highest diffusivity among all the planes in Cu.…”

Section: Introductionmentioning

confidence: 99%

Ultra-Thin Cu Nano-Twinned Films Sputtered On Si Wafers for Low Temperature Hybrid Bonding Of Advanced 3D-IC Packages

Yang,

Chen,

Chen

et al. 2024

IJMMME

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The nanotwinned structure has been attracting a great deal of attention due to its excellent mechanical and electrical properties. In this study, ultra-thin nanotwinned Cu (nt-Cu) films with a thickness of 1.5 μm were fabricated by DC magnetron sputtering with moderate substrate bias. Within these films, an equiaxed-grain transition layer only 100-400 nm thick formed between the nanotwinned region and Si substrate and was observed by focused ion beam (FIB). The XRD and EBSD analyses indicated that the as-deposited nanotwinned films had a strong (111) preferred orientation. The surface roughness of the films, as measured with an atomic force microscope (AFM), was below 10 nm, which was sufficiently smooth for chip bonding at low temperature with minor pressure. Direct bonding of Si chips sputtered with such ultra-thin nt-Cu films with a (111) preferred orientation has been evidenced to yield a sound interface, and this bonding method can be applied for the manufacturing of 3D-IC packages.

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Low-temperature and low-pressure direct copper-to-copper bonding by highly (111)-oriented nanotwinned Cu

Cited by 11 publications

References 31 publications

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

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

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

Ultra-Thin Cu Nano-Twinned Films Sputtered On Si Wafers for Low Temperature Hybrid Bonding Of Advanced 3D-IC Packages

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