Browsing by Author "Tu, King-Ning"

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Electromigration Mechanism of Failure in Flip-Chip Solder Joints Based on Discrete Void Formation
(2017-12-20)
Chang, Yuan-Wei
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Cheng, Yin
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Helfen, Lukas
;
Xu, Feng
;
Tian, Tian
In this investigation, SnAgCu and SN100C solders were electromigration (EM) tested, and the 3D laminography imaging technique was employed for in-situ observation of the microstructure evolution during testing. We found that discrete voids nucleate, grow and coalesce along the intermetallic compound/solder interface during EM testing. A systematic analysis yields quantitative information on the number, volume, and growth rate of voids, and the EM parameter of DZ*. We observe that fast intrinsic diffusion in SnAgCu solder causes void growth and coalescence, while in the SN100C solder this coalescence was not significant. To deduce the current density distribution, finite-element models were constructed on the basis of the laminography images. The discrete voids do not change the global current density distribution, but they induce the local current crowding around the voids: this local current crowding enhances the lateral void growth and coalescence. The correlation between the current density and the probability of void formation indicates that a threshold current density exists for the activation of void formation. There is a significant increase in the probability of void formation when the current density exceeds half of the maximum value.
Eliminate Kirkendall voids in solder reactions on nanotwinned copper
(2013-03-01)
Liu, Tao-Chi
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Liu, Chien-Min
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Huang, Yi-Sa
;
Chen, Chih
;
Tu, King-Ning
Electroplating was used to fabricate a high density of nanotwins that exhibited the preferred (111) orientation in Cu. We found no formation of Kirkendall voids in solder reactions on the nanotwinned Cu. This was due to the high density of steps and kinks on the nanotwin boundaries, which serve as vacancy sinks. Thus the vacancy concentration cannot reach supersaturation and nucleate voids. The finding is a significant advance in the problem of solder joint reliability in microelectronic three-dimensional integrated circuit devices. (c) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Extremely anisotropic single-crystal growth in nanotwinned copper
(2014-10-01)
Lu, Chia-Ling
;
Lin, Han-Wen
;
Liu, Chien-Min
;
Huang, Yi-Sa
;
Lu, Tien-Lin
By electroplating of nearly unidirectionally < 111 >-oriented nanotwinned and fine-grained Cu on a Si wafer surface followed by annealing at 400-500 degrees C for up to 1 h, we grew many extremely large < 100 >-oriented single crystals of Cu with sizes ranging from 200 to 400 mu m. By patterning and annealing the nanotwinned Cu films, we grew an array of < 100 >-oriented single crystals of Cu with sizes ranging from 25 to 100 mu m on Si. In comparison, single-crystal nano-wire growth is a one-dimensional anisotropic growth process, in which the growth along the axial direction is much faster than in the radial direction. We report here a bulk-type two-dimensional crystal growth of an array of numerous < 100 >-oriented single crystals of Cu on Si. This growth process has the potential for microbump applications in three-dimensional integrated circuit-packaging technology for hand-held consumer electronic products.
Fabrication of arrays of (100) Cu under-bump-metallization for 3D IC packaging
(2015)
Chiu, Wei-Lan
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Lu, Chia-Ling
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Lin, Han-Wen
;
Liu, Chien-Min
;
Huang, Yi-Sa
Due to the thousands of microbumps on a chip for 3D ICs, the precise control of the microstructure of all the material is required. The nearly < 111 >-oriented nanotwinned and fine-grained Cu was electroplated on a Si wafer surface and annealed at 400-500 C for 1 h, many extremely large < 100 > oriented Cu crystals with grain sizes ranging from 200 to 400 um were obtained. The < 111 >-oriented Cu grains were transformed into super-large < 100 >-oriented grains after the annealing. In addition, we patterned the < 111 >-oriented Cu films into pad arrays of 25 to 100 um in diameter and annealed the nanotwinned Cu pads with same conditions. An array of < 100 >-oriented single crystals Cu pads can be obtained. Otherwise, single-crystal nano wire growth displays a process by one-dimensional anisotropic growth, in which the growth along the axial direction is much faster than in the radial direction. This study reported here a bulk-type two-dimensional crystal growth of an array of numerous < 100 >-oriented single crystals of Cu on Si. The growth process in 3D IC has the potential for microbump applications packaging technology.
Failure induced by thermomigration of interstitial Cu in Pb-free flip chip solder joints
(2008-09-22)
Chen, Hsiao-Yun
;
Chen, Chih
;
Tu, King-Ning
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材料科學與工程學系
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Department of Materials Science and Engineering
Failure induced by thermomigration in Pb-free SnAg flip chip solder joints has been investigated by electromigration tests under 9.7 x 10(3) A/cm(2) at 150 degrees C. The fast interstitial diffusion of Cu atoms from underbump metallization into Sn matrix caused void formation at the passivation opening on the chip side. The Cu diffusion was driven by a large thermal gradient and led to void formation even in the neighboring unpowered bumps. When the thermal gradient is above 400 degrees C/cm, theoretical calculation indicates that the thermomigration force is greater than the electromigration force at 9.7 x 10(3) A/cm(2) stressing. (C) 2008 American Institute of Physics.
Formation Mechanism of Porous Cu3Sn Intermetallic Compounds by High Current Stressing at High Temperatures in Low-Bump-Height Solder Joints
(2016-01-01)
Lin, Jie-An
;
Lin, Chung-Kuang
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Liu, Chen-Min
;
Huang, Yi-Sa
;
Chen, Chih
Electromigration tests of SnAg solder bump samples with 15 m bump height and Cu under-bump-metallization (UBM) were performed. The test conditions were 1.45 x 10(4) A/cm(2) at 185 degrees C and 1.20 x 10(4) A/cm(2) at 0 degrees C. A porous Cu3Sn intermetallic compound (IMC) structure was observed to form within the bumps after several hundred hours of current stressing. In direct comparison, annealing alone at 185 degrees C will take more than 1000 h for porous Cu3Sn to form, and it will not form at 170 degrees C even after 2000 h. Here we propose a mechanism to explain the formation of this porous structure assisted by electromigration. The results show that the SnAg bump with low bump height will become porous-type Cu3Sn when stressing with high current density and high temperature. Polarity effects on porous Cu3Sn formation is discussed.
Heterogeneous and Homogeneous Nucleation of Epitaxial NiSi(2) in [110] Si Nanowires
(2011-01-20)
Chou, Yi-Chia
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Wu, Wen-Wei
;
Lee, Chung-Yang
;
Liu, Chun-Yi
;
Chen, Lih-Juann
We report here both heterogeneous and homogeneous nucleation of epitaxial suicide of NiSi(2) in Si nanowires grown in [110] direction by in situ observation in high-resolution transmission electron microscopy (TEM). Owing to the excellent lattice match between Si and NiSi(2), a giant epitaxial step of 2-8 nm wide forms at the interface between Si and NiSi(2) during the growth of the latter. The step formation results in two suicide/Si interfaces parallel to each other in TEM observations. Heterogeneous nucleation of NiSi(2) occurs at the intersection where the step meets the interfaces. However, we have also observed the epitaxial growth of NiSi(2) having a single interface with the Si, i.e., without a giant step. Homogeneous nucleation of NiSi(2) occurs on the single interface. Incubation time of heterogeneous nucleation of NiSi(2) has been measured by high-resolution video to be much shorter than that of homogeneous nucleation. The overall growth rate of NiSi(2) for the case of heterogeneous nucleation is faster than that for the case of homogeneous nucleation. Kinetic analysis of both types of nucleation is presented for a direct comparison in order to have a better understanding of the nucleation events.
Heterogeneous and Homogeneous Nucleation of Epitaxial NiSi2 in [110] Si Nanowires
(2011-01-20)
Chou, Yi-Chia
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Wu, Wen-Wei
;
Lee, Chung-Yang
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Liu, Chun-Yi
;
Chen, Lih-Juann
We report here both heterogeneous and homogeneous nucleation of epitaxial suicide of NiSi2 in Si nanowires grown in [110] direction by in situ observation in high-resolution transmission electron microscopy (TEM). Owing to the excellent lattice match between Si and NiSi2, a giant epitaxial step of 2-8 nm wide forms at the interface between Si and NiSi2 during the growth of the latter. The step formation results in two suicide/Si interfaces parallel to each other in TEM observations. Heterogeneous nucleation of NiSi2 occurs at the intersection where the step meets the interfaces. However, we have also observed the epitaxial growth of NiSi2 having a single interface with the Si, i.e., without a giant step. Homogeneous nucleation of NiSi2 occurs on the single interface. Incubation time of heterogeneous nucleation of NiSi2 has been measured by high-resolution video to be much shorter than that of homogeneous nucleation. The overall growth rate of NiSi2 for the case of heterogeneous nucleation is faster than that for the case of homogeneous nucleation. Kinetic analysis of both types of nucleation is presented for a direct comparison in order to have a better understanding of the nucleation events.
Homogeneous Nucleation of Epitaxial CoSi(2) and NiSi in Si Nanowires
(2009-06-01)
Chou, Yi-Chia
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Wu, Wen-Wei
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Chen, Lih-Juann
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Tu, King-Ning
;
材料科學與工程學系
Homogeneous nucleation is rare except in theory. We observed repeating events of homogeneous nucleation in epitaxial growth of CoSi(2) and NiSi silicides in nanowires of silicon by using high resolution TEM. The growth of every single atomic layer requires nucleation. Heterogeneous nucleation is prevented because of non-microreversibility between the oxide/Si and oxide/silicide interfaces. We determined the incubation time of homogeneous nucleation. The calculated and the measured nucleation rates are in good agreement. We used Zeldovich factor to estimate the number of molecules in the critical nucleus; it is about 10 and reasonable. A very high supersaturation is found for the homogeneous nucleation.
Homogeneous Nucleation of Epitaxial CoSi2 and NiSi in Si Nanowires
(2009-06-01)
Chou, Yi-Chia
;
Wu, Wen-Wei
;
Chen, Lih-Juann
;
Tu, King-Ning
;
材料科學與工程學系
Homogeneous nucleation is rare except in theory. We observed repeating events of homogeneous nucleation in epitaxial growth of CoSi2 and NiSi silicides in nanowires of silicon by using high resolution TEM. The growth of every single atomic layer requires nucleation. Heterogeneous nucleation is prevented because of non-microreversibility between the oxide/Si and oxide/silicide interfaces. We determined the incubation time of homogeneous nucleation. The calculated and the measured nucleation rates are in good agreement. We used Zeldovich factor to estimate the number of molecules in the critical nucleus; it is about 10 and reasonable. A very high supersaturation is found for the homogeneous nucleation.
Intermetallic compounds in 3D integrated circuits technology: a brief review
(2017-09-28)
Annuar, Syahira
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Mahmoodian, Reza
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Hamdi, Mohd
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Tu, King-Ning
;
材料科學與工程學系
The high performance and downsizing technology of three-dimensional integrated circuits (3D-ICs) for mobile consumer electronic products have gained much attention in the microelectronics industry. This has been driven by the utilization of chip stacking by throughSi- via and solder microbumps. Pb-free solder microbumps are intended to replace conventional Pb-containing solder joints due to the rising awareness of environmental preservation. The use of low-volume solder microbumps has led to crucial constraints that cause several reliability issues, including excessive intermetallic compounds (IMCs) formation and solder microbump embrittlement due to IMCs growth. This article reviews technologies related to 3D-ICs, IMCs formation mechanisms and reliability issues concerning IMCs with Pb-free solder microbumps. Finally, future outlook on the potential growth of research in this area is discussed.
Low temperature Cu-Cu direct bonding by (111) oriented nano-twin Cu
(2017-01-01)
Juang, Jing-Ye
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Chu, Yi-Cheng
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Lu, Chia-Ling
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Chen, Chih
;
Tu, King-Ning
In this study, a low temperature solid state diffusion bonding process with (111) highly oriented nano-twined Cu (nt-Cu) was proposed. A less void bonding interface was observed reveals a good bonding quality for the bonded samples. In addition, a large quasisingle grain was identified in the bonded film. Based on these results, it is believed that high strength and durable bonding structure can be accomplished by bonding two highly (111)-oriented nt-Cu films.
Low-temperature direct copper-to-copper bonding enabled by creep on (111) surfaces of nanotwinned Cu
(2015-05-12)
Liu, Chien-Min
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Lin, Han-Wen
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Huang, Yi-Sa
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Chu, Yi-Cheng
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Chen, Chih
Direct Cu-to-Cu bonding was achieved at temperatures of 150-250 degrees C using a compressive stress of 100 psi (0.69 MPa) held for 10-60 min at 10(-3) torr. The key controlling parameter for direct bonding is rapid surface diffusion on (111) surface of Cu. Instead of using (111) oriented single crystal of Cu, oriented (111) texture of extremely high degree, exceeding 90%, was fabricated using the oriented nano-twin Cu. The bonded interface between two (111) surfaces forms a twist-type grain boundary. If the grain boundary has a low angle, it has a hexagonal network of screw dislocations. Such network image was obtained by plan-view transmission electron microscopy. A simple kinetic model of surface creep is presented; and the calculated and measured time of bonding is in reasonable agreement.
Materials challenges in three-dimensional integrated circuits
(2015-03-01)
Chen, Kuan-Neng
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Tu, King-Ning
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
In the present era of big data and the Internet of things (the interconnection of computing devices in the Internet infrastructure), the fabrication of mobile and other electronic devices by three-dimensional integrated circuits (3D ICs) is receiving wide attention. The concept of using 3D ICs to extend the limit of Moore\'s Law of two-dimensional ICs, by combining chip technology and packaging technology, has existed for more than 10 years. However, we still do not mass produce 3D IC devices due to low yield and reliability, as well as high cost. Most problems are caused by materials selection and integration at the small scale. This issue offers a review of 3D ICs and emphasizes the materials challenges of this new technology.
Optimization of the nanotwin-induced zigzag surface of copper by electromigration
(2016)
Chen, Hsin-Ping
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Huang, Chun-Wei
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Wang, Chun-Wen
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Wu, Wen-Wei
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Liao, Chien-Neng
By adding nanotwins to Cu, the surface electromigration (EM) slows down. The atomic mobility of the surface step-edges is retarded by the triple points where a twin meets a free surface to form a zigzag-type surface. We observed that EM can alter the zigzag surface structure to optimize the reduction of EM, according to Le Chatelier\'s principle. Statistically, the optimal alternation is to change an arbitrary (111)/(hkl) zigzag pair to a pair having a very low index (hkl) plane, especially the (200) plane. Using in situ ultrahigh vacuum and high-resolution transmission electron microscopy, we examined the effects of different zigzag surfaces on the rate of EM. The calculated rate of surface EM can be decreased by a factor of ten.
Process for protecting solder joints and structure for alleviating electromigration and joule heating in solder joints
(2006-02-09)
Chen, Chih
;
Yeh, Everett Chang-Ching
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Tu, King-Ning
This invention provides a process for protecting solder joints, comprising forming an UBM or pad metallurgy in solder joints and then further forming a small solder bump on UBM or pad metallurgy between substrate and chip. Wherein a material of high electric resistance is coated at the ends of UBM or pad metallurgy where substrate is connected to chip, as to equalize the current distribution of solder bump, therefore the electromigration resistance of solder joints is improved by suppressing the current crowding and joule heating phenomenon.
Study of Discrete Voids Formation in Flip-Chip Solder Joints due to Electromigration Using In-Situ 3D Laminography and Finite-Element Modeling
(2016-01-01)
Chang, Yuan-Wei
;
Cheng, Yin
;
Xu, Feng
;
Helfen, Lukas
;
Tian, Tian
Nowadays, the microelectronics industry broadly uses the flipchip technology to enhance the packaging density. However, the small size and the unique geometry of the flip-chip solder joints induce the electromigration (EM) reliability issue. In this study, a Pb-free solder joints (SAC1205) was EM tested by a current of 7.5x10(3) A/cm(2). During the tests, a three-dimensional (3D) X-ray laminography method was applied to in-situ observe the microstructure evolution. The laminography method allows for the non-destructive observation and provides the quantitative analysis among three dimensions. After EM testing for 650 hr, a new EM failure mechanism was found rather than the well-known models, the pancake void propagation and the under-bump-metallization dissolution. According to the laminography images at different testing stages, many voids simultaneously formed and grew during the entire procedure of testing. Most of them distributed in the current crowding region, but a few also located in the low-currentdensity region. As the testing time increased, voids grew bigger, coalesced with each other, and finally became large voids which occupied the interface and caused EM failure. The finite-element (FE) method was also applied to analyze the interplay between the microstructure evolution and current density redistribution. A series of 3D FE models were built based on the laminography images at different testing stages. The current density distribution from the FE analysis indicates that the multiple voids formation does not affect the global current density distribution until the voids merged together and became very large voids in the late stage of EM testing. The relieving of the global current crowding in the pancake void model was not found in this new EM failure mechanism. It was the local current crowding found in the new model that responsible for the EM retardation.
Study of electromigration-induced formation of discrete voids in flip-chip solder joints by in-situ 3D laminography observation and finite-element modeling
(2016-09-15)
Chang, Yuan-Wei
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Cheng, Yin
;
Xu, Feng
;
Helfen, Lukas
;
Tian, Tian
In the microelectronics industry the flip-chip (FC) technology is broadly used to enhance the packaging density. However, the small size and the unique geometry of the FC solder joints induce the electro-migration (EM) reliability issue. In this study, a pair of lead-free solder joints (SAC1205) was EM tested by a current of 7.5 x 10(3) A/cm(2). During the tests, X-ray laminography was applied to observe the microstructure evolution in-situ. Laminography enables the non-destructive observation of the bump microstructure and allows for a quantitative three-dimensional (3D) analysis. After EM testing for 650 h, a new EM failure mechanism was found, differing from the two well-known models, the pancake void propagation and the under-bump-metallization dissolution. Here, a few pre-existing small voids grew and simultaneously many new voids formed and grew over the entire EM testing period. Most of the nucleating voids were distributed in the current crowding region, a few also located in the low-current density region. As the testing time increased, voids increasingly coalesced with each other, forming a porous network which occupied a large part of the interface area and caused the EM failure. A finite element (FE) method was then applied to analyze the interplay between the microstructure evolution and current density redistribution. A series of 3D FE models was built based on the laminography images for the different testing stages. The current density distribution from the FE analysis indicates that the formation of discrete voids did not affect the global current density distribution until a major coalescence of the voids occurred. The relieving of the global current crowding in the pancake void model was not found in this new EM failure mechanism. It was the local current crowding around individual void found in the new mechanism that is held responsible for the EM retardation. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Tensile Properties and Thermal Stability of Unidirectionally < 111 >-Oriented Nanotwinned and < 110 >-Oriented Microtwinned Copper
(2020-03-01)
Li, Yu-Jin
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Tu, King-Ning
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Chen, Chih
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材料科學與工程學系
;
國際半導體學院
Tensile tests on two kinds of electroplated copper foils with twins before and after annealing were performed. One electroplating parameter results in a microstructure of <110>-oriented microtwinned Cu (mt-Cu), and the other is <111>-oriented nanotwinned Cu (nt-Cu). The latter shows higher thermal stability than the former after annealing. Though the toughness for the two as-plated foils are quite close, the toughness for the <111> oriented nt-Cu increased from 34 to 74 MJ/m(3) after annealing at 250 degrees C for 3 h. In comparison, the toughness of the <110>-oriented mt-Cu remained almost the same after annealing.
Tensile Properties of < 111 >-Oriented Nanotwinned Cu with Different Columnar Grain Structures
(2020-03-02)
Li, Yu-Jin
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Tu, King-Ning
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Chen, Chih
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材料科學與工程學系
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國際半導體學院
We performed tensile tests on highly <111>-oriented nanotwinned copper (nt-Cu) foils with different columnar grain structures. For a systematic study, we altered the microstructure of the foils by tuning the electroplating electrolyte and annealing temperatures under a nitrogen atmosphere. The results show that the yield strength ranges from 300 to 700 MPa, and elongation spans from 5% to 25%. Knowing the measured twin spacing and average grain size, and combining the confined layer slip with the Hall-Petch equation, we calculated the theoretical yield strength of the nt-Cu with different microstructures, and the theoretic values match the experiment results. Owing to the unique crystal orientation properties of <111>-oriented columnar grains, dislocations induced by slip are very limited. The Schmid factor of grains along the tensile axis direction is highly identical, so the plastic deformation is much more suitably explained by the Schmid factor model. Thus, we replace the Taylor factor with the Schmid factor in the slip model of nt-Cu.