Browsing by Author "Chen, Chih"

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A new failure mechanism of electromigration by surface diffusion of Sn on Ni and Cu metallization in microbumps
(2018-04-12)
Chang, Yuan-Wei
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Hu, Chia-chia
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Peng, Hsin-Ying
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Liang, Yu-Chun
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Chen, Chih
Microbumps in three-dimensional integrated circuit now becomes essential technology to reach higher packaging density. However, the small volume of microbumps dramatically changes the characteristics from the flip-chip (FC) solder joints. For a 20 mu m diameter microbump, the cross-section area and the volume are only 1/25 and 1/125 of a 100 mu m diameter FC joint. The small area significantly enlarges the current density although the current crowding effect was reduced at the same time. The small volume of solder can be fully transformed into the intermetallic compounds (IMCs) very easily, and the IMCs are usually stronger under electromigration (EM). These result in the thoroughly change of the EM failure mechanism in microbumps. In this study, microbumps with two different diameter and flip-chip joints were EM tested. A new failure mechanism was found obviously in microbumps, which is the surface diffusion of Sn. Under EM testing, Sn atoms tend to migrate along the surface to the circumference of Ni and Cu metallization to form Ni3Sn4 and Cu3Sn IMCs respectively. When the Sn diffuses away, necking or serious void formation occurs in the solder, which weakens the electrical and mechanical properties of the microbumps. Theoretic calculation indicates that this failure mode will become even significantly for the microbumps with smaller dimensions than the 18 mu m microbumps.
Analysis of bump resistance and current distribution of ultra-fine-pitch microbumps
(2013-01-01)
Chang, Y. W.
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Peng, H. Y.
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Yang, R. W.
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Chen, Chih
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Chang, T. C.
To keep up with the demand of continuous increase in device densities, the integration of three-dimensional integrated circuits (3D-IC) has become the most probable solution, and the utilization of ultra-fine-pitch microbump has emerged as an essential component of 3D-IC technology. In this study, a Kelvin bump structure was fabricated and resistances measured at different angles on a 20.0 mu m microbump were investigated. The microbump resistance at 0 degrees, 60 degrees, 120 degrees, and 180 degrees are 74.7, 45.9, 14.6, and 13.7 m Omega, respectively. These high resistances in microbumps may result in high interconnect resistance and cause resistance/capacitance (RC) delay, and thus lower the electrical performance of 3D-IC. A series of finite-element-model (FEM) was built to analyze the distribution of electric field in microbump. The FEM results have shown that the current is distributed uniformly in the thin solder joint, but current crowding still occurs in the Cu under-bump-metallization (UBM). The finding of the current crowding in the Cu UBM is the main cause of high resistances in the microbump. Thickening the Al trace, for example, from 0.4 mu m to 1.5 mu m, is a direct solution to reduce the unexpected high microbump resistance. A numerical model which treated solder joints as a resistance network was also performed in this study. For comparison, both FEM and the numerical model show the same trend and agree with the measurement results from Kelvin bump structure. The results all point to one thing: thickening the Al trace turn out to be the most effective approach to reduce high microbump resistance. When the Al trace thickness is increased from 0.8 to 3.0 mu m, the microbump resistance is decreased to half of the original value, resulted from the alleviation of current crowding in the Cu UBM. (C) 2012 Elsevier Ltd. All rights reserved.
Anisotropic Grain Growth in (111) Nanotwinned Cu Films by DC Electrodeposition
(2020-01-01)
Lu, Tien-Lin
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Shen, Yu-An
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Wu, John A.
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Chen, Chih
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材料科學與工程學系
We have reported a method of fabricating (111)-orientated nanotwinned copper (nt-Cu) by direct current electroplating. X-ray analysis was performed for the samples annealed at 200 to 350 degrees C for an hour. X-ray diffraction indicates that the (200) signal intensity increases while (111) decreases. Abnormal grain growth normally results from transformation of surface energy or strain energy density. The average grain size increased from 3.8 mu m for the as-deposited Cu films to 65-70 mu m after the annealing at 250 degrees C for 1 h. For comparison, no significant grain growth behavior was observed by random Cu film after annealing for an hour. This research shows the potential for its broad electric application in interconnects and three-dimensional integrated circuit (3D IC) packaging.
Anisotropic grain growth to eliminate bonding interfaces in direct copper-tocopper joints using < 111> -oriented nanotwinned copper films
(2018-12-01)
Chu, Yi-Cheng
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Chen, Chih
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材料科學與工程學系
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Department of Materials Science and Engineering
Grain growth in Cu-to-Cu bonding was investigated at 250 degrees C and 300 degrees C. With highly [111]-oriented nanotwinned Cu (nt-Cu) films, bonding can be achieved with the aid of high diffusivity on Cu (111) surfaces at 250 degrees C for 1 h. Yet, recrystallization did not occur at this annealing condition. However, recrystallization and anisotropic grain growth took place at 250 degrees C for 2 h and 300 degrees C for 0.5 h. The bonding interface was eliminated and extremely large Cu grains grew. The temperature of 250 degrees C is the lowest temperature ever reported for elimination of the bonding interface. For comparison, the Cu joints fabricated by ordinary Cu films did not have obvious grain growth at 300 degrees C for 0.5 h.
Asymmetrical growth of Cu6Sn5 intermetallic compounds due to rapid thermomigration of Cu in molten SnAg solder joints
(2012-10-01)
Guo, Ming-Yung
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Lin, C. K.
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Chen, Chih
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Tu, K. N.
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材料科學與工程學系
We observed asymmetrical growth of Cu6Sn5 intermetallic compounds (IMCs) on the two interfaces of Cu/SnAg/Cu solder joints during reflow at 260 degrees C on a hot plate. The IMCs grew to 12.3 mu m on the cold end and 3.5 mu m on the hot end after reflow for 40 min. However, the consumption of Cu on the cold end is less than that on the hot end. We propose that rapid thermomigration of Cu is responsible for the asymmetrical growth of the IMCs. With the simulated thermal gradient of 51 degrees C/cm across the liquid solder, the heat of transport of Cu is calculated as 20 kJ/mol. (C) 2012 Elsevier Ltd. All rights reserved.
Blocking hillock and whisker growth by intermetallic compound formation in Sn-0.7Cu flip chip solder joints under electromigration
(2010-05-01)
Liang, S. W.
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Chen, Chih
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Han, J. K.
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Xu, Luhua
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Tu, K. N.
Mass extrusion occurs in electromigration at the anode in cross-sectioned Sn-0.7Cu flip-chip solder joints. In a pair of joints, the hillock squeezed out at the anode on the board side is more serious than the whisker grown at the anode on the chip side. The difference of mass extrusion has been found to be affected by the amount of intermetallic compound (IMC) formation in the solder bump. It is found that when a large amount of Cu-Sn IMCs form in the grain boundaries of Sn grains, small hillocks are extruded on the anode end. It is proposed that the excessive IMC formation may be able to block the diffusion path of Sn atoms, so the growth of both the Sn whiskers and hillocks are retarded. (C) 2010 American Institute of Physics. [doi:10.1063/1.3410796]
Bump Resistance Change Behavior due to Cu-Sn IMCs Formation with Various Solder Diameters
(2015)
Hsieh, Wan-Lin
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Lin, Chung-Kuang
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Zhan, Chau-Jie
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Huang, Yu-wei
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Chen, Chih
Theoretical calculation and simulation of FEM were proposed to explain the decline of change in resistance in Cu-Sn microbumps during the electromigration test. The IMC transformation from Cu6Sn5 to Cu3Sn was supposed to be the reason. Being aware that the dimension keeps shrinking, the behavior for various solder diameters was also investigated.
Characterization and field-emission properties of carbon nanotube arrays in nanoporous alumina template and on blank Si substrate
(2006-11-15)
Yang, Ching-Jung
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Chen, Chih
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Shieh, Jia-Min
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材料科學與工程學系
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Department of Materials Science and Engineering
Ordered carbon nanotube (CNT) arrays were synthesized within anodized aluminum oxide template by thermal decomposition of hydrocarbon precursor with hydrogen ambient at growth temperature as low as 500 degrees C. Excess hydrogen in precursor mixture enables a steady supply of mobile hydrocarbon reactant which promotes facile solid-phase diffusion. The activation energy for CNT growth was determined to be 0.55 eV, a number smaller than 1.02 eV for similar precursor in nitrogen ambient. Moreover, CNTs grown in anodized aluminum oxide nanopores in this low temperature process were found to exhibit unusually high field-emission current of 100 mA/cm(2) at 8 V/mu m. (c) 2006 American Institute of Physics.
Chip-to-chip copper direct bonding in no-vacuum ambient using (111) oriented nano-twinned copper
(2018-01-01)
Juang, Jing Ye
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Shie, Kai Cheng
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Li, Yu Jin
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Lin, Benson
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Chang, Chia Cheng
In this study, we demonstrate the chip-to-chip copper direct bonding by using (111) oriented nano-twinned copper in N-2 ambient, without vacuum. A well bonded interface in the Cu-to-Cu joint was identified by the focus ion beam (FIB) microstructure observation. The secondary electron images (SEI) showed a void-less bonding interface within the bonded Cu joint. In addition, a die shear test was conducted. The test result revealed that the Cu joint has a robust bonded Cu structure due to its high value. The shear strength is more than 100 MPa. There is nearly twice strength value higher than the traditional SnAg solder joint (64 MPa). In addition, the scanning electron microscope (SEM) image showed the joint fractured in a ductile manner. Besides, we also performed the resistance measurement by using Kelvin probes on the bonded chip-to-chip test vehicle. The result showed 4.12 m Omega in single joint resistance and 4.26 x 10(-8) Omega.cm(2) in contact resistivity. More than 30% resistance reduction has been confirmed as compared to the traditional SnAg solder joint (6.32 m Omega). Moreover, for further post annealing process on the bonded test vehicle, we can further reduce the joint resistance by the value of 2.9 m Omega. It approaches the value of bulk Cu. The evidences revealed that the Cu-to-Cu joint is superior to the traditional SnAg solder. In last, the chip-to-chip copper direct bonding by using (111) oriented nano-twinned copper in N-2 ambient was achieved.
Communication-Formation of Porous Cu3Sn by High-Temperature Current Stressing
(2016)
Lin, C. K.
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Chen, Chih
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Chu, David T.
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Tu, K. N.
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材料科學與工程學系
Cu3Sn is a compound commonly formed in solder joints on Cu. In this study, two different Cu3Sn structures were observed at different stages of current stressing. A normal layer-type and pore-less Cu3Sn structure was obtained at the current density of 2.27 x 10(4) A/cm(2) at 222 degrees C after 12 h. However, a porous Cu3Sn structure was formed under the same current stressing conditions after 22 h. The formation of porous Cu3Sn is explained by the mechanisms of phase transformation and reaction. The porous Cu3Sn structure is frequently observed in Cu/solder/Cu microbumps with a reduced solder height after electromigration tests. (C) 2016 The Electrochemical Society. All rights reserved.
Communication-Growth of <111> Nanotwinned Nickel Films on <111> Nanotwinned Cu Substrates
(2017-10-03)
Chu, Yi-Cheng
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Chen, Chih
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材料科學與工程學系
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Department of Materials Science and Engineering
Nickel has a high twinning energy of 110 MJ/m(2), and it is thus difficult to fabricate nanotwinned Ni (nt-Ni) films. In this study, we adopt <111>-oriented nanotwinned Cu films as a substrate for the growth of nt-Ni films, and successfully electroplate <111>-oriented Ni films with densely-packed nanotwins. The average twin spacing is only 22 nm, while the grain size is over 1 mu m. The nt-Ni film can be grown to a thickness of approximately 2.6 mu m; beyond that, the Ni film becomes nanocrystalline. This approach provides a promising method to fabricate <111>-oriented nt-Ni films with controlled microstructures. (C) 2017 The Electrochemical Society. All rights reserved.
Comparison of oxidation in uni-directionally and randomly oriented Cu films for low temperature Cu-to-Cu direct bonding
(2018-07-13)
Tseng, Chih-Han
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Tu, K. N.
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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
Cu-to-Cu direct bonding has attracted attention because it has been implemented in CMOS image sensors. Prior to the bonding, the oxides on the Cu surface needs to be removed, yet the surface may oxidize right after cleaning. Thus, oxidation is an inherent issue in the application of Cu direct bonding. Our previous study reported that Cu direct bonding can be achieved below 250 degrees C by using (111)-oriented nanotwinned Cu because it has the fastest surface diffusivity. However, the oxidation behavior of the nanotwinned Cu is unclear. Here, we examined the oxidation behavior of highly (111) and (200) oriented, and randomly-oriented Cu films at temperatures ranging from 120 to 250 degrees C. Transmission electron microscopy was used to measure the oxide thickness. The results show that the oxidation rate of (111)-oriented nanotwinned Cu has the lowest oxidation rate among them. Together, it is unique to possess the combination of the fastest surface diffusivity and the lowest oxidation rate.
Concentration Gradient of Ni in Reduced SnAg Thickness in Ni/SnAg/Cu Microbumps during Solid-State Aging
(2013)
Liu, Tao-Chi
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Huang, Yi-Sa
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Chen, Chih
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材料科學與工程學系
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Department of Materials Science and Engineering
We investigate the cross-interaction in Cu/SnAg/Ni microbumps with a reduced solder thickness of 30 and 10 mu m. The concentration of Ni atoms at the opposite site increased with the decrease in solder-height. A considerable concentration gradient of Ni was detected in 10-mu m microbumps sample, which strongly triggers the diffusion of Ni atoms to the Cu side. The diffused Ni atoms at Cu side form the ternary intermetallic compounds of (Cu,Ni)(6)Sn-5, which possesses a lower free energy than Cu6Sn5 does. Eventually, the growth of the Cu3Sn was inhibited due to the formation of the thermodynamically stable (Cu, Ni) 6Sn5. (C) 2012 The Electrochemical Society. All rights reserved.
Copper direct bonding with short time and excellent electrical property by < 111 >-oriented nano-twinned copper
(2019-01-01)
Shie, Kai Cheng
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Juang, Jing-Ye
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Chen, Chih
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材料科學與工程學系
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Department of Materials Science and Engineering
In order to be compatible with semiconductor manufacturing, nanotwinned Cu microbumps were fabricated on 8 '' wafers. The pair of top and bottom dies were jointed through thermal compression bonding. After 1 min bonding time, the resistance could obtaine from all test structures, which indicates all the microbumps were bonded in the short time successfully.
Copper-to-Copper direct bonding on highly (111) oriented nano-twinned copper in no-vacuum ambient
(2017-01-01)
Juang, Jing-Ye
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Lu, Chia-Ling
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Chen, Kuan-Ju
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Chang, Tao-Chih
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Chen, Chih
In this study, we achieve the Cu-to-Cu direct bonding by using the (111) oriented nano-twined-Cu in N-2 ambient, without vacuum condition and no additional thermal annealing treatment is needed. A well bonded interface under a temperature gradient between 400 degrees C and 100 degrees C was identified by the evidence of the grown grain across the bonding interface. In addition, a creep assisted bonding mechanism for the Cu-Cu direct bonding is proposed. Moreover, a shear test was applied on the bonded joints for the investigation of the bonded joint strength and its fracture mode. The mean value of joint strength is 176 MPa which is significantly higher than the conventional solder joint. In summary, the Cu-to-Cu direct bonding by (111) oriented nt-Cu in no-vacuum ambient as well as the grain evolution across the bonding interface has been achieved and verified.
Copper-to-copper direct bonding on highly (111)-oriented nanotwinned copper in no-vacuum ambient
(2018-09-17)
Juang, Jing-Ye
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Lu, Chia-Ling
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Chen, Kuan-Ju
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Chen, Chao-Chang A.
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Hsu, Po-Ning
A vacuum-free Cu-to-Cu direct bonding by using (111)-oriented and nanotwinned Cu has been achieved. A fast bonding process occurs in 5 min under a temperature gradient between 450 and 100 degrees C. It is verified by grain growth across the bonded interface. To investigate the grain growth behavior, further annealing in the temperature gradient, as well as in a reversed temperature gradient, was performed. They showed similar recrystallization behavior with de-twinning. To analyze the de-twinning, we recall the classic model of annealing twin formation by Fullman and Fisher as comparison. Our case is opposite to the model of Fullman and Fisher. A mechanism of direct bonding by surface diffusion creep is proposed.
Core-Shell Ni-NiO Nano Arrays for UV Photodetection without an External Bias
(2012)
Liu, Chien-Min
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Chen, Chih
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Tseng, Yuan-Chieh
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材料科學與工程學系
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Department of Materials Science and Engineering
This work demonstrates a simple method for fabricating a nano-structured device that performs notable photodetecting capabilities. With a template of anodic aluminum oxide, highly ordered Ni-NiO nano core-shell arrays were fabricated by annealing the electroless-deposited Ni arrays at 300 degrees C for 30 minutes. High-resolution transmission electron microscopy (HRTEM) demonstrated that a NiO layer with a thickness of similar to 5 nm was developed on the surface of the Ni arrays. The effects of annealing time and temperature on NiO were probed by HRTEM. Results show that temperature has a greater effect on the development of NiO. The Ni/NiO interface forms naturally a Schottky nanojunction, which covers most of the array surface when patterned with an indium-tin oxide (ITO) electrode. The ITO/Ni-NiO/Si device was found to yield photocurrent when exposed to ultraviolet (UV) light without an external voltage bias. The device takes great advantage of the large junction area and one-dimensional configuration of the core-shell array, displaying rapid photoresponse to UV light and subsequent steady photocurrent. These features make the proposed device a viable alternative to the UV photodetector. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.067204jes] All rights reserved.
Correlation between the Microstructures of Bonding Interfaces and the Shear Strength of Cu-to-Cu Joints Using (111)-Oriented and Nanotwinned Cu
(2018-12-01)
Juang, Jing-Ye
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Lu, Chia-Ling
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Li, Yu-Jin
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Tu, K. N.
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Chen, Chih
Highly (111)-oriented Cu pillar-bumps were bonded to highly (111)-oriented Cu films at temperatures ranging from 200 degrees C/100 degrees C to 350 degrees C/100 degrees C in N-2 ambient conditions. The microstructures of the bonded interfaces affected the shear strength performance of the bonded Cu joints. The bonded interfaces at 300 degrees C/100 degrees C and 350 degrees C/100 degrees C had far fewer voids than interfaces bonded at 200 degrees C/100 degrees C and 250 degrees C/100 degrees C. In addition, grain growth took place across the bonding interfaces at temperatures above 300 degrees C/100 degrees 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 degrees C/100 degrees C, but became ductile after bonded above 300 degrees C/100 degrees 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.
Coupled microstructural and magnetic transition in Co-doped Ni nano-arrays
(2011-10-01)
Yang, Chao-Yao
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Huang, Chun-Chao
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Tseng, Yuan-Chieh
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Liu, Chien-Min
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Chen, Chih
A superparamagnetic (SM) to ferromagnetic (FM) phase transition was investigated in Co-doped (similar to 6%) electroless plated Ni arrays. The introduction of Co altered the microstructure of the Ni arrays from nanocrystalline to polycrystalline, resulting in a SM -> FM transition. This Co-induced magnetic phase transition is similar to that observed after heat treatment of undoped samples [C. M. Liu, Y. C. Tseng, C. Chen, M. C. Hsu, T. Y. Chao, and Y. T. Cheng, Nanotechnology 20, 415703 (2009); C. C. Huang, C. C. Lo, Y. C. Tseng, C. M. Liu, and C. Chen, J. Appl. Phys. 109, 113905 (2011)]. The role of Co dopant was identified electronically using x-ray magnetic spectroscopy, revealing that the transition modified the Ni host's electronic structure and enhanced its moment by effectively spin-polarizing the Ni 3d conduction band. This was distinctly different than in the heat treatment case, which underwent an electronically independent phase transition. The element-specific magnetic hysteresis of Co and Ni was also probed, which showed that the two elements were magnetically coupled. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3647753]
Direct measurement of hot-spot temperature in flip-chip solder joints under current stressing using infrared microscopy
(2008-08-01)
Hsiao, Hsiang-Yao
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Liang, S. W.
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Ku, Min-Feng
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Chen, Chih
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Yao, Da-Jeng
Several simulation studies reported that a hot spot exists in flip-chip solder bumps under accelerated electromigration. Yet, there are no experimental data to verify it. In this paper, the temperature distribution during electromigration in flip-chip SnAg3.5 solder bumps is directly inspected using infrared microscopy. Two clear hot spots are observed in the bump. One is located at the region with peak current density and the other one is at the bump edge under the current-feeding metallization on the chip side. Under a current stress of 1.06x10(4) A/cm(2), the temperature in the two hot spots are 161.7 and 167.8 degrees C, respectively, which surpass the average bump temperature of 150.5 degrees C. In addition, the effect of under-bump-metallization (UBM) thickness on the hot spots is also examined. It indicates that the hot-spot temperature in the solder bump increases for the solder joints with a thinner UBM. Electromigration test indicates that these hot spots have significant influence on the initial failure location. (c) 2008 American Institute of Physics.