Wafer-level Cu–Sn micro-joints with high mechanical strength and low Sn overflow

Duan, Ani; Luu, Thi-Thuy; Wang, Kaiying; Aasmundtveit, Knut E.; Høivik, Nils

doi:10.1088/0960-1317/25/9/097001

Cited by 12 publications

(3 citation statements)

References 15 publications

(27 reference statements)

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“…In response to these diverse challenges, Cu-Sn solid-liquid interdiffusion (SLID) bonding presents an attractive solution. It has the potential to simultaneously enable hermetic sealing for MEMS and high-density, short signal path electrical interconnects for the integration of MEMS and integrated circuits (ICs) [3], [7], [18], [19], [20]. However, the process temperature of Cu-Sn SLID bonding exceeds 250 °C, and the typical procedure involves electroplating Cu and Sn on both wafers to be bonded [15], [16], [17].…”

Section: Introductionmentioning

confidence: 99%

Novel low-temperature interconnects for 2.5/3D MEMS integration: demonstration and reliability

Emadi,

Vuorinen,

Liu

et al. 2024

Preprint

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In response to the evolving demands of microelectromechanical system (MEMS) integration, aiming to achieve high-performance electronic products, innovative interconnect solutions are becoming essential. The interconnects must possess key features, including the capability for miniaturization, low processing temperatures, and the ability to maintain a stable microstructure with optimized electrical, mechanical, and thermomechanical properties. To meet these demands, this study designed a novel Cu-Sn-based solid-liquid interdiffusion (SLID) interconnect. The study involved the implementation of a metallization stack, incorporating Co as a layer to interact with low-temperature Cu-Sn-In SLID and form intermetallic compounds (IMCs). Since Cu6(Sn,In)5 forms at a lower bonding temperature than other phases commonly observed in the Cu-Sn-In system, the study aimed to develop interconnects comprising a stable single-phase (Cu,Co)6(Sn,In)5. Bonding conditions were established for the Cu-Sn-In/Co system and the Cu-Sn/Co system as a reference. Thorough assessments of their thermomechanical reliability were conducted through hightemperature storage (HTS), thermal shock (TS), and tensile tests. The Cu-Sn-In/Co system emerged as a reliable low-temperature solution with the following key attributes: 1) a reduced bonding temperature compared to the Cu-Sn SLID interconnects, 2) the absence of the Cu3Sn phase and resulting void-free interconnects, and 3) high thermomechanical reliability, particularly following thermal annealing after bonding.

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Section: Introductionmentioning

confidence: 99%

Novel low-temperature interconnects for 2.5/3D MEMS integration: demonstration and reliability

Emadi,

Vuorinen,

Liu

et al. 2024

Preprint

View full text Add to dashboard Cite

show abstract

“…Traditionally, the Au-Sn eutectic bonding process proceeds at the temperature range of 280 • C-350 • C [14,15], involving solid-liquid diffusion bonding or instantaneous liquidphase bonding. However, this method carries the risk of Sn extrusion, leading to potential short-circuits [16,17]. Additionally, the high bonding temperature engenders significant residual thermal stress, weakening the module and device reliability [18].…”

Section: Introductionmentioning

confidence: 99%

A Method for Fast Au-Sn Bonding at Low Temperature Using Thermal Gradient

Wang,

Liu,

Qiu

et al. 2023

Micromachines

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Flip chip bonding technology on gold–tin (Au-Sn) microbumps for MEMS (Micro Electro Mechanical Systems) and 3D packaging is becoming increasingly important in the electronics industry. The main advantages of Au-Sn microbumps are a low electrical resistance, high electrical reliability, and fine pitch. However, the bonding temperature is relatively high, and the forming mechanism of an intermetallic compound (IMC) is complicated. In this study, Au-Sn solid-state diffusion (SSD) bonding is performed using the thermal gradient bonding (TGB) method, which lowers bonding temperature and gains high bonding strength in a short time. Firstly, Au-Sn microbumps with a low roughness are prepared by using an optimized process. Then, Au-Sn bonding parameters including bonding temperature, bonding time, and bonding pressure are optimized to obtain a higher bonding quality. The shear strength of 23.898 MPa is obtained when bonding in the HCOOH environment for 10 min at the gradient temperature of 150 °C/250 °C with a bonding pressure of more than 10 MPa. The IMC of Au-Sn is found to be Au-Sn and Au5Sn. The effect of annealing time on the IMC is also investigated. More and more Au5Sn is generated with an increase in annealing time, and Au5Sn is formed after Sn is depleted. Finally, the effect of annealing time on the IMC is verified by using finite element simulation, and the bonding strength of IMC was found to be higher when the bonding temperature is 150 °C at the cold side and 250 °C at the hot side. The temperature in the bonding area can reach 200 °C, which proves that the Au-Sn bonding process is solid-state diffusion because the temperature gradient reaches 2500 °C/cm.

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“…Solder bonding methods using SnPb solder, Pb-free solder and copper pillars are applied early in the solder bump connection of the flip-chip packaging. For higher high-temperature stability and finer-pitch interconnects, solid–liquid interdiffusion (SLID) (including Cu-Sn [Bosco and Zok, 2004; Bosco and Zok, 2005; Duan et al , 2015; Luu et al , 2013]) and solid–state diffusion bonding (including lead-free solder, Au-Sn [Wang et al , 2007] and Sn-Ag-Cu [Higurashi et al , 2014]) methods have been developed. Considering better anti-electromigration, electrical and thermal performance, copper direct bonding draws lots of attention.…”

Section: Introductionmentioning

confidence: 99%

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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Wafer-level Cu–Sn micro-joints with high mechanical strength and low Sn overflow

Cited by 12 publications

References 15 publications

Novel low-temperature interconnects for 2.5/3D MEMS integration: demonstration and reliability

Novel low-temperature interconnects for 2.5/3D MEMS integration: demonstration and reliability

A Method for Fast Au-Sn Bonding at Low Temperature Using Thermal Gradient

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

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Wafer-level Cu–Sn micro-joints with high mechanical strength and low Sn overflow

Cited by 12 publications

References 15 publications

Novel low-temperature interconnects for 2.5/3D MEMS integration: demonstration and reliability

Novel low-temperature interconnects for 2.5/3D MEMS integration: demonstration and reliability

A Method for Fast Au-Sn Bonding at Low Temperature Using Thermal Gradient

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

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Product

Resources

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