Browsing by Author "Li, Yu-Jin"

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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
;
Tu, K. N.
;
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.
Growth of Cu6Sn5 and Cu3Sn Intermetallic compounds on (111)-, (100)-, and randomly-oriented copper films.
(2016)
Li, Yu-Jin
;
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
Sn whisker has been found since 1940s.[1] The formation mechanism of whiskers was controversial. There were two possible mechanisms. Some scientists thought whisker formation were the result of recrystallization or abnormal grain growth, however others suggested that the atomic migration of Cu caused by compressive stress gradient were the main driving force of whisker formation. In latest study, Han-wen Lin et al. found that the whiskers growth mechanism is highly related with the growth of intermetallic compounds. The results showed that (100)- or (111)-oriented copper can slow down the growth of intermetallic compounds (IMCs) and whiskers growth. This can prove that the driving force of whiskers is compressive stress gradient produced by serious IMCs formation. As mentioned above, the growth of IMCs plays an important role in whisker formation, and copper are widely used as under bump metallization (UBM) so now we are interesting in the research of the growth mechanism of Cu6Sn5 and Cu3Sn IMCs. Our lab can fabricate highly (111)-oriented nano-twinned copper film and after annealing at appropriate temperature we can get (100)-oriented copper with large grain size. These copper films will serve as substrate. After certain duration of aging test, the results showed that the IMCs of copper and tin grew relatively fast along tin grain boundary. Also, we found that the growth of Cu6Sn5 and Cu3Sn was inhibited on (100)- and (111)-oriented copper films, and the grain of IMCs grew large in randomly-oriented copper film. So we suggest grain boundary diffusion of tin dominate IMCs formation in Cu/Sn system. Moreover, the IMC growth rate on (100)-oriented copper films are even slower than (111)-oriented copper films.
High Electromigration Lifetimes of Nanotwinned Cu Redistribution Lines
(2019-01-01)
Tseng, I-Hsin
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Li, Yu-Jin
;
Lin, Benson
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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.
High-toughness (111) nano-twinned copper lines for fan-out wafer-level packaging
(2019-01-01)
Li, Yu-Jin
;
Hsu, Wei-Yu
;
Lin, Benson
;
Chang, ChiaCheng
;
Chen, Chih
In the present paper, the nt-Cu were electroplated on the InFO test vehicles with 5 mu m line width to compare the reliability with the normal electroplated copper. The temperature of the TCT ranges from -55 to 125 degrees C. The microstructure of the copper traces after 200 cycles and 1000 cycles was shown in the results. The nt-Cu RDL is much stronger than the normal Cu in the thermal cycling test. In order to understand the mechanical property of the nt-Cu and the normal Cu, tensile tests of electroplated copper foils was employed. After annealing at 250 degrees C for 3 hours, the toughness of nt-Cu (about 60MJ/m(3)) is much higher than normal copper (about 30MJ/m(3)). In addition, the simulation results shows that the maximum stress on the copper trace during the TCT is about 200MPa which is much lower than the yield point of nt-Cu. In other word, the nt-Cu would return to original size when the stress removed without strain accumulation. In summary, we observed that the nt-Cu performs much better than normal copper in TCT. From the tensile test and simulation, we can understand the mechanical behavior and the typical reason for the high reliability of nt-Cu.
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.
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
;
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
;
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.