Browsing by Author "Liu, Tao-Chi"

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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.
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
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Chen, Chih
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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
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Lin, Han-Wen
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Liu, Chien-Min
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Huang, Yi-Sa
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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 and Characterization of (111)-Oriented and Nanotwinned Cu by Dc Electrodeposition
(2012-10-01)
Liu, Tao-Chi
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Liu, Chien-Min
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Hsiao, Hsiang-Yao
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Lu, Jia-Ling
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Huang, Yi-Sa
We report an approach to fabricating (111)-oriented and nanotwinned Cu (nt-Cu) by dc electroplating. A 200 nm thick Cu with (111) preferred orientation is required as a seed layer. Highly oriented Cu films with densely packed nanotwins can be grown to exceed 20 mu m thick at high current and high stirring speeds. X-ray diffraction indicates that the intensity ratio of (111) to (220) is as high as 506, which is the highest among the reported electroplated Cu films. The spacing of twins ranges from 10 to 100 nm, which reveals a high hardness value of 2.23 GPa. The (111)-oriented nt-Cu will have many potential applications in interconnects and 3D IC packaging.
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
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Liu, Chien-Min
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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.
Innovative methodologies of circuit edit by focused ion beam (FIB) on wafer-level chip-scale-package (WLCSP) devices
(2011-10-01)
Liu, Tao-Chi
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Chen, Chih
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Liu, Shih-Ting
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Chang, Ming-Lun
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Lin, Jandel
As packaging technology advances to wafer level chip scale packaging (WLCSP) to enable reduced chip size and manufacturing cost, circuit edit has become a critical issue for the fully packaged integrated circuits (ICs). These advanced package types cannot be rebuilt on a single chip; therefore, function testing after circuit edit of WLCSP faces challenges. Furthermore, there are routings at the redistribution layer of WLCSP ICs. Circuit edit was applied on both the chip and the package level. In this paper the focused ion beam was applied to mill the organic material of the package structure to expose underlying ICs, instead of chemically destroying the packaging. Metal line cutting and conductive path deposition were also developed by a beam-based technique. These new approaches make the direct edit of electrical circuitry possible not only in ICs but also at package level. Therefore, for the debug process and for failure analysis, the WLCSP ICs have negligible damage and negligible signal integrity loss by retaining the original packaging structure.
Novel EBSD preparation method for Cu/Sn microbumps using a focused ion beam
(2012-12-01)
Liu, Tao-Chi
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Chen, Chih
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Chiu, Kuo-Jung
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Lin, Han-Wen
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Kuo, Jui-Chao
We proposed a novel technique developed from focused ion beam (FIB) polishing for sample preparation of electron backscatter diffraction (EBSD) measurement. A low-angle incident gallium ion beam with a high acceleration voltage of 30 kV was used to eliminate the surface roughness of cross-sectioned microbumps resulting from mechanical polishing. This work demonstrates the application of the FIB polishing technique to solders for a high-quality sample preparation for EBSD measurement after mechanical polishing. (C) 2012 Elsevier Inc. All rights reserved.
Unidirectional Growth of Microbumps on (111)-Oriented and Nanotwinned Copper
(2012-05-25)
Hsiao, Hsiang-Yao
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Liu, Chien-Min
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Lin, Han-Wen
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Liu, Tao-Chi
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Lu, Chia-Ling
Highly oriented [111] Cu grains with densely packed nanotwins have been fabricated by direct-current electroplating with a high stirring rate. The [111]-oriented and nanotwinned Cu (nt-Cu) allow for the unidirectional growth of Cu6Sn5 intermetallics in the microbumps of three-dimensional integrated-circuit packaging; a uniform microstructure in a large number of microbumps of controlled orientation can be obtained. The high-density twin boundaries in the nt-Cu serve as vacancy sinks during the solid-state reaction between Pb-free solder and Cu and greatly reduce the formation of Kirkendall (or Frenkel) voids.