Grain Structure Analysis of Cu/SiO<sub>2</sub> Hybrid Bond Interconnects after Reliability Testing

Panchenko, Iuliana; Wambera, Laura; Mueller, Maik; Rudolph, Catharina; Hanisch, Anke; Bartusseck, Irene; Wolf, Marcus

doi:10.1109/estc48849.2020.9229743

Cited by 10 publications

(15 citation statements)

References 7 publications

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“…The preparation steps before bonding include CMP, cleaning and plasma activation of the Cu/SiO2 wafer surface [12]. The top and the bottom wafers were aligned in a wafer bonder (EVG Gemini) and brought into contact at room temperature and without bonding pressure.…”

Section: A Sample Descriptionmentioning

confidence: 99%

“…Two types of the reliability tests were carried out in our previous publication [12]: 1) temperature shock test at -40/125 °C (TST) according to JESD-22-A104C:2005 standard; and 2) isothermal storage (high temperature storage, HTS) according to JESD22-A103C:2004 standard. This paper additionally presents the results after multiple bonding cycles (2, 3 ,5, and 9).…”

Section: B Reliability Tests and Characterizationmentioning

confidence: 99%

“…While reliability data for Cu/SiO2 hybrid bonds is available, comprehensive studies on the microstructure are relatively rare. The microstructure and reliability of Cu/Cu hybrid bond interconnects was investigated in our previous publication [12] and will be further evaluated with additional testing conditions in the current publication. Kim et al [13] analyzed the influence of annealing temperature on the grain size distribution and the grain orientation of small Cu pads for Cu/Cu hybrid bonding.…”

Section: Introductionmentioning

confidence: 99%

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Microstructure Development of Cu/SiO₂ Hybrid Bond Interconnects After Reliability Tests

Panchenko

Wambera

Mueller

et al. 2022

IEEE Trans. Compon., Packag. Manufact. Technol.

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The focus of this study is a detailed characterization of hybrid Cu/SiO2 wafer-to-wafer bonding interconnects after reliability testing. Hybrid bonding (or direct bond interconnect) is a technology of choice for fine pitch bonding without microbumps. The main challenge of the hybrid bonding technology is the preparation of a clean Cu/SiO2 surface with controlled Cu dishing. The Cu/Cu interface after hybrid bonding and after reliability testing was investigated by electron backscatter diffraction (EBSD) in this study. The Cu interconnects (diameter 4 μm and pitch 18 μm) enclosed by SiO2 were formed by wafer-to-wafer bonding. The small diced stacks were used for subsequent reliability tests. Three types of tests were carried out: temperature shock test (TST) at -40 °C / 125 °C up to 1000 cycles, isothermal storage at 150 °C, 300 °C, and 400 °C as well as multiple bonding cycles. The results include a comprehensive estimation of the changes in grain diameter, grain boundaries and texture of the interconnects. All samples showed good reliability and stayed intact after all tests. Grain refinement was observed after TST, storage at 150 °C, and multiple bonding cycles compared to the state after bonding. Grain growth was found for the storage at 300/400 °C (up to 6 h). No significant changes in texture were found after the reliability tests. The <111> direction with its characteristic <115> twin orientation are the dominating orientations perpendicular to the bonding interface. The migration of 60 ° twin boundaries has been observed after reliability testing. The results indicate a rotation towards nearby high angle grain boundaries (60 to 45 °).

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Section: A Sample Descriptionmentioning

confidence: 99%

Section: B Reliability Tests and Characterizationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Microstructure Development of Cu/SiO₂ Hybrid Bond Interconnects After Reliability Tests

Panchenko

Wambera

Mueller

et al. 2022

IEEE Trans. Compon., Packag. Manufact. Technol.

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“…They reported that the coefficient of thermal expansion (CTE) of SiO 2 is smaller than that of Cu. Thus, the Cu–Cu bumps were under compression at an elevated temperature, and no obvious defects were formed [ 34 ].…”

Section: Introductionmentioning

confidence: 99%

“…The highest surface diffusivity of a (111) Cu surface can enhance the surface creep bonding during thermal compression bonding processes [22,29]. To examine the Cu-to-Cu direct bonding quality, various reliability tests were conducted [33,34]. A shear strength greater than 100 MPa was obtained by eliminating the bonding interface [33].…”

Section: Introductionmentioning

confidence: 99%

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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Recent progress on bumpless Cu/SiO₂ hybrid bonding for 3D heterogeneous integration

Kang

Niu

et al. 2022

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Purpose Bumpless Cu/SiO2 hybrid bonding, which this paper aims to, is a key technology of three-dimensional (3D) high-density integration to promote the integrated circuits industry’s continuous development, which achieves the stacks of chips vertically connected via through-silicon via. Surface-activated bonding (SAB) and thermal-compression bonding (TCB) are used, but both have some shortcomings. The SAB method is overdemanding in the bonding environment, and the TCB method requires a high temperature to remove copper oxide from surfaces, which increases the thermal budget and grossly damages the fine-pitch device. Design/methodology/approach In this review, methods to prevent and remove copper oxidation in the whole bonding process for a lower bonding temperature, such as wet treatment, plasma surface activation, nanotwinned copper and the metal passivation layer, are investigated. Findings The cooperative bonding method combining wet treatment and plasma activation shows outstanding technological superiority without the high cost and additional necessity of copper passivation in manufacture. Cu/SiO2 hybrid bonding has great potential to effectively enhance the integration density in future 3D packaging for artificial intelligence, the internet of things and other high-density chips. Originality/value To achieve heterogeneous bonding at a lower temperature, the SAB method, chemical treatment and the plasma-assisted bonding method (based on TCB) are used, and surface-enhanced measurements such as nanotwinned copper and the metal passivation layer are also applied to prevent surface copper oxide.

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Grain Structure Analysis of Cu/SiO₂ Hybrid Bond Interconnects after Reliability Testing

Cited by 10 publications

References 7 publications

Microstructure Development of Cu/SiO₂ Hybrid Bond Interconnects After Reliability Tests

Microstructure Development of Cu/SiO₂ Hybrid Bond Interconnects After Reliability Tests

Failure Mechanisms of Cu–Cu Bumps under Thermal Cycling

Recent progress on bumpless Cu/SiO₂ hybrid bonding for 3D heterogeneous integration

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Grain Structure Analysis of Cu/SiO2 Hybrid Bond Interconnects after Reliability Testing

Cited by 10 publications

References 7 publications

Microstructure Development of Cu/SiO₂ Hybrid Bond Interconnects After Reliability Tests

Microstructure Development of Cu/SiO₂ Hybrid Bond Interconnects After Reliability Tests

Failure Mechanisms of Cu–Cu Bumps under Thermal Cycling

Recent progress on bumpless Cu/SiO2 hybrid bonding for 3D heterogeneous integration

Contact Info

Product

Resources

About

Grain Structure Analysis of Cu/SiO₂ Hybrid Bond Interconnects after Reliability Testing

Recent progress on bumpless Cu/SiO₂ hybrid bonding for 3D heterogeneous integration