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    28 July 2022, Volume 28 Issue 7
    Special Issue on Electronic Electroplating
    Preface to Special Issue on Electronic Electroplating
    Zhi-Dong Chen, Chong Wang, Wei He, Ming Li
    2022, 28(7):  2104401.  doi:10.13208/j.electrochem.210440
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    Author Spotlight
    2022, 28(7):  2104601.  doi:10.13208/j.electrochem.210460
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    Research Progress of Copper Electrodeposition Filling Mechanism in Silicon Vias
    Yun-Na Sun, Yong-Jin Wu, Dong-Dong Xie, Han Cai, Yan Wang, Gui-Fu Ding
    2022, 28(7):  2213001.  doi:10.13208/j.electrochem.2213001
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    Aiming at the electroplating filling problem of deep via TSV (through silicon via) interconnection, the multi-compatible integrated manufacturing technology team at the Shanghai Jiao Tong University has completed the numerical solution of the equations and realized the numerical simulation of TSV filling mode by applying the finite element method with arbitrary Lagrange Euler algorithm. The filling mechanisms of blind vias, the butterfly filling form for the through vias and the simultaneous filling mode of vias with different aspect ratios are analyzed by simulation, contributing to the parameter optimization and sample manufacturing. The effects of electroplating current density and heat treatment temperature on the mechanical properties of electroplating filled TSV-Cu were investigated by in-situ compression test and uniaxial film tensile test. With the increase of heat treatment temperature, the fracture strength and yield strength decreased significantly, and the Young's modulus changed slowly in a corrugated shape. The influence of the current density was more complexed. Based on the above research results, the thermal deformation mechanism of interconnection structure caused by thermal mismatch stress was studied through the self-built in-situ testing system, which gives change in the real-time deformation of TSV-Cu with temperature. The results showed that the thermal deformation process can be divided into the elastic deformation stage, the quasi plastic strengthening stage and the plastic deformation stage.

    Electrodeposition of Functional Epitaxial Films for Electronics
    Kui Huang, Rong-Jiao Huang, Su-Qin Liu, Zhen He
    2022, 28(7):  2213006.  doi:10.13208/j.electrochem.2213006
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    Electrodeposition is a solution-based synthesis technique that can be used to fabricate various functional materials on conductive or semiconductive substrates under ambient conditions. Electrodeposition is usually triggered by an artificial electric stimulation (i.e., applied potential/current) to the substrate to oxidize or reduce ions, molecules, or complexes in the deposition solution layer near the substrate surface, which drives this solution layer to depart from its thermodynamic equilibrium and consequently causes the assembly of targeted deposits on the substrate. During electrodeposition, many experimental parameters could affect the properties of the deposits in different ways. To date, many elements (both metals and nonmetals), compounds (e.g., metal oxides, hydroxides, and chalcogenides), and composites have been electrodeposited, mostly as either polycrystalline, textured, or epitaxial films. Among them, the epitaxial films are a kind of single-crystal-like films grown with certain out-of-plane and in-plane orientations. Due to the highly ordered atomic arrangement in epitaxial films, they usually exhibit unique electric and magnetic properties. In this review, the common synthetic routes for the electrodeposition as well as the key experimental parameters that affect the epitaxial growth of the deposits are summarized. Besides, techniques used to characterize epitaxial films are briefly introduced. Furthermore, the electrodeposited functional epitaxial films with special electronic, electromagnetic, and photovoltaic properties are discussed.

    Research Progress in Electroless Cobalt Plating and the Bottom-up Filling of Electroless Plating
    Yu Shen, Bing-Bing Li, Yi Ma, Zeng-Lin Wang
    2022, 28(7):  2213002.  doi:10.13208/j.electrochem.2213002
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    With the continuous improvement of semiconductor integration, the resistivity of copper interconnect lines increases rapidly. When the width of the interconnect line is close to 7 nm, the resistivity of copper becomes the same as that of cobalt. International Business Machines Corporation (IBM) and Advanced Semiconductor Incorporation (ASI) have used cobalt to replace copper as a next-generation interconnect material. However, the fabrication of the cobalt seed layer and the super filling of electroplating cobalt for the 7 nm via-holes have been still the large challenge. Electroless plating is a very simple method to form a seed layer on the surface of an insulator. By the bottom-up filling of electroless plating, via-holes with several nanometers could be filled completely. In this paper, the research progress in electroless cobalt plating is reviewed, and the effects of the reductant species on the deposition rate and the film quality of electroless cobalt plating are analyzed. Meanwhile, based on long-term and a lot of studies, a bottom-up filling of electroless cobalt plating for 7 nm via-hole in semiconductor cobalt interconnects is proposed.

    Effect of Corrosion Inhibitors on Copper Etching to Form Thick Copper Line of PCB in Acidic Etching Solution
    Xiao-Li Wang, Wei He, Xian-Ming Chen, Hong Zeng, Yuan-Zhang Su, Chong Wang, Gao-Sheng Li, Ben-Xia Huang, Lei Feng, Gao Huang, Yuan-Ming Chen
    2022, 28(7):  2213007.  doi:10.13208/j.electrochem.2213007
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    The chemical compounds of 2-mercaptobenzothiazole (2-MBT), benzotriazole (BTA) and phenoxyethanol (MSDS) as corrosion inhibitors were used to inhibit the copper etching to form the thick copper line of PCB in the acidic etching solution. The inhibition status was characterized with contact angle measurement, electrochemical test and etch factor calculation, while the corrosion morphology of copper surface was studied by scanning electron microscope. The adsorption mechanism of corrosion inhibitors on copper surface is analyzed by molecular dynamics and quantum chemistry calculations. The results indicated that the synergistic function of the two inhibitors could effectively promote their adsorption on the copper surface in parallel, while their adsorption energy could be higher than that of the single inhibitor. The etch factor of the thick copper line with about 33 μm in thickness increased to 6.59 from the etching solution with 2-MBT and MSDS for good agreement of PCB manufacture.

    Mechanism and Application of Nickel Nano-Cone by Electrodeposition on a Flexible Substrate
    Xiu-Ren Ni, Ya-Ting Zhang, Chong Wang, Yan Hong, Yuan-Ming Chen, Yuan-Zhang Su, Wei He, Xian-Ming Chen, Ben-Xia Huang, Zhen-Lin Xu, Yi-Feng Li, Neng-Bin Li, Yong-Jie Du
    2022, 28(7):  2213008.  doi:10.13208/j.electrochem.2213008
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    Nano-array structure possesses promising prospect in power supply, optical device and electronic manufacturing. In this paper, a black nickel nano-cone array was prepared on a flexible substrate by galvanostatic deposition and the corresponding factors involved in the fabrication of nickel nano-cone array was explored. Experimental results showed that a large current density and low main salt concentration were not favored to the formation of cone nickel structure. It was also found that ammonium chloride, as the crystal modifier, was crucial to deposit the uniform nano-cone array. In addition, the growth mechanism of nickel nano-cone was further studied by molecular dynamics simulation. The excellent wettability and light absorption of nickel nano-cone array were investigated, which demonstrates potential applications of the nickel nano-cone array.

    Investigation of Through-Hole Copper Electroplating with Methyl Orange as A Special Leveler
    Jia-Ying Xu, Shou-Xu Wang, Yuan-Zhang Su, Yong-Jie Du, Guo-Dong Qi, Wei He, Guo-Yun Zhou, Wei-Hua Zhang, Yao Tang, Yu-Yao Luo, Yuan-Ming Chen
    2022, 28(7):  2213003.  doi:10.13208/j.electrochem.2213003
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    Methyl Orange (MO) with two kinds of functional groups can act as both an accelerator and an inhibitor, which has been used as a special leveler to simplify the electroplating additive system in the through-hole (TH) copper electroplating experiments. In this work, the role of MO in TH electroplating is characterized by molecular dynamics simulations and quantum chemical calculations. It is suggested that MO can spontaneously flatten the copper surface and be well adsorbed on the cathode surface, which inhibit the copper electrodeposition on the cathode. Electrochemical behavior of MO was evaluated by galvanostatic measurements (GM) and cyclic voltammetry (CV) to confirm that MO hardly affects the potential due to its duel functions of depolarizing and polarizing effects from the molecular structure of sulfonic acid group and other groups to achieve the internal Cu2+ reduction acceleration and mass transfer inhibition. Throw power value of TH with the aspect ratio of 10:1 could reach 92.34% from the base plating solution bath with the additions of only EO/PO and MO. The study of MO could provide new ideas for the development of electroplating additive system.

    Electrodeposition Mechanism and Process of a Novel Cyanide-Free Gold Sulfite Bath
    Jia-Qiang Yang, Lei Jin, Wei-Qing Li, Zhao-Yun Wang, Fang-Zu Yang, Dong-Ping Zhan, Zhong-Qun Tian
    2022, 28(7):  2213005.  doi:10.13208/j.electrochem.2213005
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    A novel cyanide-free gold sulfite process is introduced in this paper. In the bath, chloauric acid was directly employed as the main salt, and hydroxyethylidene diphosphonic acid (HEDP) was used as the stabilizer and coating grain refiner. The bath stability, the gold coating morphology and the mechanism of gold electrodeposition were studied in detail. The results showed that HEDP could significantly improve the bath stability. Moreover, the grains of the gold coating obtained from the gold sulfite bath without HEDP was rod-like, which grew gradually with the increasing of the deposition time, resulting in that the appearance of the coating turned from a golden yellow to a hazy reddish brown by the increase of the coating thickness. As HEDP was introduced into the gold sulfite bath, the gold grains were transformed to pyramidal, and the grain growth rate accompanying the increase of the coating thickness was much slower than that in the gold sulfite bath without HEDP, observing the golden bright appearance within 1 μm thickness. Electrochemical curves indicated that gold electrodeposition did not undergo a nucleation stage.

    Electrochemical Deposition of Copper Pillar Bumps with High Uniformity
    Bai-Zhao Tan, Jian-Lun Liang, Zi-Liang Lai, Ji-Ye Luo
    2022, 28(7):  2213004.  doi:10.13208/j.electrochem.2213004
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    Electrochemical deposition of copper pillar bumps (CPBs) is one of the key technologies for the advanced packaging. In this study, the effects of the additive concentration, the electrolyte convection, the current density, and the electroplating system on the uniformity of the CPBs have been systematically investigated. The results showed that the profiles of the CPBs were mainly determined by the additive concentration, the bath convection and the current density, while the heights of the CPBs were mainly affected by the electroplating system. For the CPBs profiles, it was found that the low leveler concentration and high current density would generally result in domed shape, while the uneven agitation would lead to inclined surface. For the heights of CPBs, the macroscopic uniformity could be dramatically improved by a sophisticatedly designed electroplating system. These results can provide basic guidance for the optimization of the CPBs electroplating.