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Effect of Reverse Currents during Electroplating on the < 111 >-Oriented and Nanotwinned Columnar Grain Growth of Copper Films
(2020-06-03)
Chen, Kuan-Ju
;
Wu, John A.
;
Chen, Chih
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Nanotwinned copper (nt-Cu) has been attracting a great deal of attention in the past decades due to its excellent mechanical and electrical properties. In this study, a new approach, periodic-reverse (PR) waveforms, is adopted to electroplate nt-Cu films with highly < 111 >-oriented columnar grain microstructures. We investigate the effect of the reverse current on the microstructures of < 111 >--oriented nt-Cu films and their grain growth behavior. With proper reverse current parameters, we are able to obtain a nt-Cu film with a significantly thin transition layer, low amount of impurities, and low residual stress levels in comparison to a DC electroplated film. It is also discovered that the grain size after annealing of the nt-Cu film is related to its initial columnar grain microstructures, which can be tailored by the reverse current parameter. These results show that PR electroplating provides a promising approach in improving and controlling the microstructures and properties of nt-Cu films.
Tensile Properties of < 111 >-Oriented Nanotwinned Cu with Different Columnar Grain Structures
(2020-03-02)
Li, Yu-Jin
;
Tu, King-Ning
;
Chen, Chih
;
材料科學與工程學系
;
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.
Ultra-high annealing twin density in < 211 >-oriented Cu films
(2020-07-15)
Chen, Kuan-Ju
;
Chen, Jui-Yuan
;
Ting, Yi-Hsin
;
Wu, Wen-Wei
;
Chen, Chih
We reported the fabrication of densely twinned Cu films with highly (211) texture developed from the annealing of <111>-oriented nanotwinned copper (nt-Cu) films. During the annealing at 300 degrees C, abnormal grain growth occurred in the nt-Cu film and resulted in a microstructure dominated by the anomalously large <211>-oriented grains. Moreover, densely-intersected annealing twin bands with <221>, <611>, and <931> orientations are embedded in the large <211> grains. The measured annealing twin density is 0.2 mu m(-1), which is highest among the reported values in previous literatures with similar grain size. Extensive multiple twinning process may occur during the annealing to form the unique microstructure. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Instant Cu-to-Cu direct bonding enabled by < 111 >-oriented nanotwinned Cu bumps
(2020-02-01)
Shie, Kai Cheng
;
Juang, Jing-Ye
;
Chen, Chih
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Cu-to-Cu direct bonding was successfully achieved in 10 s with < 111 >-oriented nanotwinned Cu (nt-Cu) bumps in ambient N-2. The bonding temperature and pressure were 300 degrees C and 90 MPa, respectively. A nearly void-free interface and a low bump resistance of 4.9 m Omega can be observed after a short-time bonding process. Besides, longer bonding times of 60 s and 30 s were employed, but the resistances of the Cu joints did not decrease significantly when the bonding time increased to 60 s. However, the nt-Cu columnar grains started to recrystallize during the 60 s bonding and started detwinning in 10 s bonding. Yet, the bonding interface remained under such a short bonding time. (C) 2019 The Japan Society of Applied Physics
Tensile Properties and Thermal Stability of Unidirectionally < 111 >-Oriented Nanotwinned and < 110 >-Oriented Microtwinned Copper
(2020-03-01)
Li, Yu-Jin
;
Tu, King-Ning
;
Chen, Chih
;
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.
Fabrication and Characterization of < 100 >-Oriented Quasi-single Crystalline Cu Lines
(2020-03-01)
Lu, Tien-Lin
;
Wu, John A.
;
Chen, Chih
;
材料科學與工程學系
;
Department of Materials Science and Engineering
Nanotwinned copper (nt-Cu) films with < 111 > crystal orientation were electroplated on Si wafers by pulse plating, with original grain size of similar to 1.4 mu m. By patterning and annealing the nt-Cu film at 450-500 degrees C for 1 h, we can grow a large number of < 100 >-oriented quasi-single crystal Cu lines that are 200 and 500 pm in length and 60 pm in width. We perform anisotropic grain growth on a Si substrate to fabricate quasi-single crystal Cu lines array of < 100 > crystal orientation. These large < 100 > Cu single crystals may have potential applications as interconnects in three-dimensional integrated circuit technology.
Anisotropic Grain Growth in (111) Nanotwinned Cu Films by DC Electrodeposition
(2020-01-01)
Lu, Tien-Lin
;
Shen, Yu-An
;
Wu, John A.
;
Chen, Chih
;
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.
Extremely rapid grain growth in scallop-type Cu6Sn5 during solid-liquid interdiffusion reactions in micro-bump solder joints
(2020-04-01)
Gusak, A. M.
;
Tu, K. N.
;
Chen, Chih
;
材料科學與工程學系
;
Department of Materials Science and Engineering
In 3D IC technology, when the size of the micro-bump solder joint is reduced to 10 mu m, the scallop-type Cu6Sn5 grains on opposite sides of the joint can interact directly by contacting each other during the solid-liquid interdiffusion reaction. Upon contact, an extremely rapid grain growth of the scallops occurs. We propose that the liquid solder wets the grain boundary between scallops and provides an extremely fast kinetic path of liquid channel for grain growth. The width of the liquid channel has been estimated to be about 1.5 nm. This is a unique phenomenon observed in micro-bump solid joints. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Highly (111)-oriented Nanotwinned Cu for High Fatigue Resistance in fan-out wafer-level packaging
(2019-01-01)
Li, Yu-Jin
;
Theng, Chih-Han
;
Tseng, I-Hsin
;
Chen, Chih
;
Lin, Benson
Fanout wafer level packaging is a potential solution for combining high electrical performance and low cost. However, with the shrinkage of the package, the mechanical reliability of the copper redistribution layer becomes an important issue. However, based on the processing of fan out packaging, the copper lines were annealed several times during the process. The annealing process is harmful to traditional strengthen mechanisms, but not to columnar grains with high density twinning structure. In this study, the technology of electroplating highly <111>-oriented copper lines was introduced to solve the reliability issue in copper RDLs. By the nature of nano-twinned Cu, the performance of thermal cycling test (TCT) lifetime is much better than normal copper, and the failure mechanisms were discussed in this study.
High Electromigration Lifetimes of Nanotwinned Cu Redistribution Lines
(2019-01-01)
Tseng, I-Hsin
;
Li, Yu-Jin
;
Lin, Benson
;
Chang, Chia-Cheng
;
Chen, Chih
In this paper, we measured the electromigration lifetimes for nanotwinned copper (nt-Cu) and regular copper redistribution lines (RDLs) for 3D-ICs packaging. The width of the RDLs is 10 mu m in width and 5 mu m in thickness, and the lines were coated by polyimide. The average lifetime of the nt-Cu RDL copper line is 445 hours to reach 1.2 times of its initial resistance. However, it takes 160 hours to reach the same resistance increase for regular copper RDL line. The nt-Cu has better EM lifetime than regular copper.

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