Finite Element Simulation of Solid–Liquid Interdiffusion Bonding Process: Understanding Process-Dependent Thermomechanical Stress

Tiwary, Nikhilendu; Vuorinen, Vesa; Ross, Glenn; Paulasto‐Kröckel, Mervi

doi:10.1109/tcpmt.2022.3170082

Cited by 6 publications

(4 citation statements)

References 41 publications

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“…The total thickness of the electroplated Cu and Sn stack from top and bottom wafer was ≈15 μm, so the reduction in thickness of the final bond line is attributed to the squeeze out of liquid Sn. Moreover, formation of voids could be seen in the test structures concentrated mostly at the Cu/Cu 3 Sn interface, which is widely reported due to interplay of various parameters, such as Kirkendall voiding and impurities incorporation in the electroplated structures [14], [15]. The resistance of the two-bump test structures measured varied from 6 to 7 and 3 to 4 for the 25-and 50-μm test structure, respectively.…”

Section: Resultsmentioning

confidence: 85%

Impact of Inherent Design Limitations for Cu–Sn SLID Microbumps on Its Electromigration Reliability for 3D ICs

Tiwary

Ross

Vuorinen

et al. 2023

IEEE Trans. Electron Devices

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Continuous scaling of package architectures requires small volume and high-density microbumps in 3D stacking, which often result in solders fully transforming to intermetallic compounds (IMCs). Cu-Sn solid-liquid interdiffusion (SLID) bonding is an attractive technology where the μbumps are fully composed of IMCs. In this work, test structures made up of Cu 3 Sn IMC μbump with a lateral dimension of 25 μm × 25 μm and 50 μm × 50 μm, respectively, were manufactured on a pair of 4-inch Si wafers demonstrating wafer-level bonding capability. Electromigration (EM) tests were performed for accelerated conditions at a temperature of 150 • C for various current densities ranging from ≈2 × 10 4 to 1 × 10 5 A/cm 2 . Scanning electron microscopy (SEM) and elemental dispersive spectroscopy (EDS) were employed to characterize the as-fabricated test structures. Due to Sn squeeze out, Cu 3 Sn was formed at undesired location at the upper Cu trace. Both nondestructive [lock-in thermography (LiT)] and destructive techniques were employed to analyze the failure locations after EM tests. It was observed that the likelihood of failure spots is the current crowding zone along the interconnects in 3D architectures, which gets aggravated due to the formation of Cu 3 Sn in undesirable locations. Thermal runaway was observed even in Cu 3 Sn, which has been shown to be EM-resistant in the past, thus underlining inherent design issues of μbumps utilizing SLID technology.

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Section: Resultsmentioning

confidence: 85%

Impact of Inherent Design Limitations for Cu–Sn SLID Microbumps on Its Electromigration Reliability for 3D ICs

Tiwary

Ross

Vuorinen

et al. 2023

IEEE Trans. Electron Devices

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“…For 200 °C and 150 °C, Cu6Sn5 IMC layer was incorporated. The bonding methodology was adopted as reported in our earlier publication [10]. The Young's modulus and Poisson's ratio of Cu3Sn and Cu6Sn5 were incorporated from [11].…”

Section: Methodsmentioning

confidence: 99%

Low-temperature die attach for power components: Cu-Sn-In solid-liquid interdiffusion bonding

Emadi

Liu

Klami

et al. 2022

2022 14th International Conference on Advanced Semiconductor Devices and Microsystems (ASDAM)

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Based on the finite element (FE) simulations done in this work, lowering the bonding temperature significantly decreases the bonding induced residual stresses. Therefore, low temperature Cu-Sn-In SLID process was utilized to bond Si to Si and Si to sapphire under various bonding conditions. The microstructural evolution and the (thermo-) mechanical properties of the joints were studied. The results showed that the Cu-Sn-In SLID bonds composed of a single Cu6(Sn,In)5 IMC phase with high joint strength. Furthermore, the hardness and Young's modulus of Cu6(Sn,In)5 formed in the SLID bonding were measured to be slightly higher than that of binary Cu6Sn5.

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“…To achieve such high-performance smart sensors, the 3D heterogeneous integration of components, miniaturized interconnect technologies, and the encapsulation of many MEMS components are required [4], [5], [6], [7]. Advanced miniaturized interconnects are needed to merge the MEMS sensors and transducers with application-specific integrated circuits (ASICs) and microcontroller units (MCUs) for edge processing [8], [9]. The hermetic encapsulation of MEMS is typically established by wafer bonding of a MEMS device wafer to a cap wafer [3], [10], [11], [12].…”

Section: Introductionmentioning

confidence: 99%

“…The hermetic encapsulation of MEMS is typically established by wafer bonding of a MEMS device wafer to a cap wafer [3], [10], [11], [12]. However, the pursuit of high-functional-performance electronic products necessitates reliable bonding methods with a low processing temperature and low residual stresses in both the sensitive MEMS elements and the entire package [7], [9]. Simultaneously, the low bonding temperature might not compromise the subsequent process steps, and therefore the newly formed interconnect areas should have a high remelting temperature [13], [14].…”

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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Finite Element Simulation of Solid–Liquid Interdiffusion Bonding Process: Understanding Process-Dependent Thermomechanical Stress

Cited by 6 publications

References 41 publications

Impact of Inherent Design Limitations for Cu–Sn SLID Microbumps on Its Electromigration Reliability for 3D ICs

Impact of Inherent Design Limitations for Cu–Sn SLID Microbumps on Its Electromigration Reliability for 3D ICs

Low-temperature die attach for power components: Cu-Sn-In solid-liquid interdiffusion bonding

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

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