Browsing by Author "Chu, Yi-Cheng"

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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.
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.
Effect of Sn grain orientation and strain distribution in 20-mu m-diameter microbumps on crack formation under thermal cycling tests
(2017-11-01)
Chu, Yi-Cheng
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Chen, Chih
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Kao, Nicholas
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Jiang, Don Son
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材料科學與工程學系
The thermo-mechanical properties of microbumps serving as interconnects between Si chips in three-dimensional integrated circuits were examined in this study. Arrays of SnAg microbumps were subjected to temperature cycling tests up to 2500 cycles. Extensive cracks formed in the microbumps, and some of them propagated across the entire microbump. A microstructural analysis by electron back scattering diffraction indicated that the cracks propagated along two paths: Sn grain boundaries with high misorientation angles and SnAg/Ni3Sn4 interfaces. The average Sn grain size was only 7.4 mu m, implying a large proportion of grain boundaries per unit volume, which facilitated crack propagation across the microbump of 20 mu m in diameter.
Electromigration in microbumps with Cu-Sn intermetallic compounds
(2016)
Chu, Yi-Cheng
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Zhan, Chau-Jie
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Lin, Han-Wen
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Huang, Yu-Wei
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Chen, Chih
The electromigration test of the microbump interconnects with Cu/Cu6Sn5/Cu structure is reported in this study. This Cu6Sn5 intermetallic compound layer was single-crystal like. The diameter of the microbumps in die-to-die stacking was 30 mu m. Test vehicles were applied by a current density of 2.2x10(5) A/cm(2) and settled on a hotplate at 150 degrees C. The resistances of the microbumps were simultaneously monitored by the four point probe during the test procedure. The Cu6Sn5 transformed into Cu3Sn in the early stage and porous Cu3Sn generated in the Cu6Sn5 layer at later stages. The morphology of porous Cu3Sn could be caused by the current direction. The decomposition of Cu6Sn5 into Cu3Sn and Sn occurs during the EM test. The migration of Sn atoms to the periphery of the under-bump-metallization was forced by the current stress, which may be the mechanism of the pore formation with the pore volume of 41.4%. More porous Cu3Sn was found in the cathode end which was an evidence of the EM effect. Finite element analysis was used to do some calculation based on theoretical stoichiometry and microstructures in the test results. The resistivity of porous Cu3Sn structure which was about 30 mu Omega-cm which was three times larger than that of Cu3Sn. The porous Cu3Sn may threaten the reliability issues of microbumps.
Fabrication of (111) nanotwinned Cu and its applications in interconnects of microelectronic devices
(2016)
Chen, Chih
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Liu, Chien-Min
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Lu, Tien-Lin
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Lin, Han-wen
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Chu, Yi-Cheng
Growth competition between layer-type and porous-type Cu3Sn in microbumps
(2017-12-01)
Chu, David T.
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Chu, Yi-Cheng
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Lin, Jie-An
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Chen, Yi-Ting
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Wang, Chun-Chieh
Experimental study of growth competition between the co-existing layer-type and porous-type Cu3Sn in solder microbumps of Cu/SnAg/Cu is reported. The thickness of the SnAg solder is about 14 pm and the Cu column on both sides is 20 pm. Upon wetting-reflow, the solder is reacted completely to form Cu Sn iptermetallic compounds in a multi-layered structure of Cu/Cu3Sn/Cu6Sn5/Cu3Sn/Cu. Upon further annealing at 220 degrees C and 260 C, we obtain Cu/Cu3Sn/porous Cu3Sn/Cu3Sn/Cu, in which both types of Cu3Sn co-exist and form an interface. In the layer-type growth, we assume Cu to be the dominant diffusing species, coming from the Cu column. The Cu reacts with Cu6Sn5 to grow the Cu3Sn layer. In the porous-type growth, we assume Sn to be the dominant diffusing species, coming from the depletion of Sn in Cu6Sn5. The depleted Cu6Sn5 transforms to the porous-type Cu3Sn. At the same time, the Sn diffuses to the side-wall of Cu column to form a coating of Cu3Sn. Experimental observations of 3-dimensional distribution of voids in the porous-type Cu3Sn are performed by synchrotron radiation tomography; the voids are interconnected for the out-diffusion of Sn. The competing growth between the layer-type and the porous-type Cu3Sn is analyzed. (C) 2017 Elsevier Ltd. All rights reserved.
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
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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 and low pressure copper-to-copper direct bonding enabled by creep on highly (111)-oriented Cu surfaces
(2015)
Tseng, Chih-Han
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Liu, Chien-Min
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Lin, Han-wen
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Chu, Yi-Cheng
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Chen, Chih
Cu-to-Cu microbumps have many advantages, such as better electrical and thermal conductivities. The Cu-to-Cu microbumps may be a potential solution to the heat dissipation problem in 3D IC integration. In addition, for packaging of CMOS image sensors, the bonding temperature is preferred to below 200 degrees C. Therefore, low temperature and low pressure Cu-to-Cu direct is of great interests for packaging industry. However, it is a challenging issue because Cu atoms diffuse slowly below 200 degrees C. In this study, we achieved low temperature and low pressure Cu bonding using highly (111)-orientated Cu films. Because the diffusivity of Cu atoms on the (111) surface diffusivity is the fastest among all the crystallographic planes of Cu. The bonding temperature can be lowered to 150 degrees C at a compressive stress of 114 psi held for 60 min at 10-3 torr. Since the melting points of popular Pb-free solders such as SnAg and SnAgCu are over 230 degrees C. Therefore the present technique can be applied to packaging of CMOS image sensors and 3D IC integration.
LOW-TEMPERATURE AND LOW-PRESSURE DIRECT COPPER-TO-COPPER BONDING BY HIGHLY (111)-ORIENTED NANOTWINNED CU
(2016)
Chen, Chih
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Liu, Chien-Min
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Lin, Han-Wen
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Huang, Yi-Sa
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Chu, Yi-Cheng
As the size of microbumps continues to shrink, the amount of solder decreases gradually, resulting the brittleness of solder joints due to formation of intermetallic compounds. Low-temperature Cu-to-Cu direct bonding appears to be one of the solutions for fine-pitch microbumps for 3D IC packaging. However, the high bonding temperature and pressure are the main problems of this approach. We achieve low-temperature Cu-to-Cu direct bonding at low pressure and ordinary vacuum. In addition, the cleaning process is simple. To bond the electroplated Cu films, the samples were cut into 3 x 3-mm(2) pieces. Then, the pieces were cleaned in acetone for 5 min, dried with a N-2 purge, cleaned with a mixed solution of HCl and deionized water (DI) water for 30 sec, rinsed with DI water, and purged with N-2 gas again. The bonding temperature can be lowered to 150 degrees C at a compressive stress of 114 psi held for 60 min at 10-3 torr, or at 200 degrees C at for 30 min. The temperature is lower than the reflow temperature of 250 degrees C for most Pb-free solders. We achieve low-temperature bonding using electroplate highly (111)-oriented nanotwinned Cu (nt-Cu) films. Excellent bonding interface can be accomplished by bonding two highly (111)-oriented nt-Cu films. In addition, excellent interface with few voids can be achieved between a highly (111)-oriented nt-Cu film and a randomly-oriented Cu film. Our breakthrough is based on the finding that the (111) orientation of the Cu surface is critical for bonding. The diffusivity of Cu atoms on (111) surfaces is approximately 3-4 orders higher than other major planes. The (111) plane allows for fast surface diffusion, which enables low-temperature creep to occur. The bonded interface between two (111) surfaces forms a twist-type grain boundary (GB). If the GB has a low angle, it has a hexagonal network of screw dislocations. The hexagonal network image was obtained by plan-view transmission electron microscopy. A simple kinetic model of surface creep will be presented. Our breakthrough provide a potential solution with a huge impact to the interconnect materials in 3D IC. The detail results will be presented in the conference.
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
;
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.
Low-temperature direct copper-to-copper bonding enabled by creep on highly (111)-oriented Cu surfaces
(2014-05-01)
Liu, Chien-Min
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Lin, Han-Wen
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Chu, Yi-Cheng
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Chen, Chih
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Lyu, Dian-Rong
We achieve low-temperature Cu-to-Cu direct bonding using highly (1 1 1)-orientated Cu films. The bonding temperature can be lowered to 200 degrees C at a stress of 114 psi for 30 min at 10(-3) torr. The temperature is lower than the reflow temperature of 250 degrees C for Pb-free solders. Our breakthrough is based on the finding that the Cu (1 1 1) surface diffusivity is the fastest among all the planes of Cu and the bonding process can occur through surface diffusion creep on the (1 1 1) surfaces. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.