Corresponding Author

Zeng-Lin Wang(wangzl@snnu.edu.cn)


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.

Graphical Abstract


electroless cobalt plating, bottom-up filing, electroless copper plating, super electroless cobalt plating, copper interconnects, cobalt interconnects

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[1] Beyne S, Dutta S, Pedreira O V, Bosman N, Adelmann C, De Wolf I, Tokei Z, Croes K. The first observation of p-type electromigration failure in full ruthenium interconnects[C]. Beyne S, IEEE International Reliability Physics Symposium, USA: IEEE, 2018.

[2] Sondheimer E H. The mean free path of electrons in metals[J]. Adv. Phys., 2001, 50(6): 499-537.
doi: 10.1080/00018730110102187 URL

[3] Mont F W, Zhang X Y, Wang W, Kelly J J, Standaert T E, Quon R, Ryan E T. Cobalt interconnect on same copper barrier process integration at the 7 nm node[C]. Mont F W, 2017 IEEE International Interconnect Technology Conference (IITC), USA: IEEE, 2017.

[4] Wen D W, Kuwahara H, Kato H, Kobayashi M, Sato Y, Masaki T, Kakihana M. Anomalous orange light-emitting (Sr,Ba)2SiO4: Eu2+ phosphors for warm white LEDs[J]. ACS Appl. Mater. Interfaces, 2016, 8(18): 11615-11620.
doi: 10.1021/acsami.6b02237 URL

[5] Webb E, Witt C, Andryuschenko T, Reid J. Integration of thin electroless copper films in copper interconnect metallization[J]. J. Appl. Electrochem., 2004, 34(3): 291-300.
doi: 10.1023/B:JACH.0000015618.02583.f7 URL

[6] Ni X R, Chen Y M, Jin X F, Wang C, Huang Y Z, Hong Y, Su X H, Zhou G Y, Wang S X, He W, Chen Q G. Investigation of polyvinylpyrrolidone as an inhibitor for trench super-filling of cobalt electrodeposition[J]. J. Taiwan Inst. Chem. Eng., 2020, 112: 232-239.
doi: 10.1016/j.jtice.2020.06.010 URL

[7] Buckalew B, Oberst J, Ponnuswamy T. Electrodeposited cobalt for advanced packaging applications[C]. Buckalew, 2017 IEEE Electron Devices Technology and Manufacturing Conference (EDTM), USA: IEEE, 2017.

[8] Kongstein O E, Haarberg G M, Thonstad J. Current efficiency and kinetics of cobalt electrodeposition in acid chloride solutions. Part I: The influence of current density, pH and temperature[J]. J. Appl. Electrochem., 2007, 37(6): 669-674.
doi: 10.1007/s10800-007-9299-z URL

[9] Pearlstein F, Weightman R F. Electroless cobalt deposition from acid baths[J]. J. Electrochem. Soc., 1974, 121: 1023-1023.
doi: 10.1149/1.2401971 URL

[10] Frieze A S, Sard R, Weil R. Some properties of electroless cobalt[J]. J. Electrochem. Soc., 1968, 115: 586-586.
doi: 10.1149/1.2411348 URL

[11] Khan M R, Lee J I. Comparison of plated Co-P and sputtered Co-Re as recording media based on nucleation, growth, structure, and magnetics[J]. J. Appl. Phys., 1985, 57(8): 4028-4030.
doi: 10.1063/1.334660 URL

[12] Hwang B J, Lin S H. Reaction mechanism of electroless deposition: Observations of morphology evolution during nucleation and growth via tapping mode AFM[J]. J. Ele-ctrochem. Soc., 1995, 142(11): 3749-3754.

[13] Liu W L, Hsieh S H, Tsai T K, Chen W J. Growth kinetics of electroless cobalt deposition by TEM[J]. J. Electro-chem. Soc., 2004, 151(10): C680-C683.
doi: 10.1149/1.1793691 URL

[14] Yu Y D, Song Z L, Ge H L, Wei G Y. Preparation of CoP films by ultrasonic electroless deposition at low initial temperature[J]. Prog. Nat. Sci., 2014, 24(3): 232-238.
doi: 10.1016/j.pnsc.2014.04.004 URL

[15] Magagnin L, Sirtori V, Seregni S, Origo A, Gavallotti P L. Electroless Co-P for diffusion barrier in Pb-free soldering[J]. Electrochim. Acta, 2005, 50(23): 4621-4625.
doi: 10.1016/j.electacta.2004.10.098 URL

[16] Chang Y H, Lin C C, Hung M P, Chin T S. The microstructure and magnetic properties of electroless-plated Co-B thin films[J]. J. Electrochem. Soc., 1986, 133(5): 985-988.
doi: 10.1149/1.2108782 URL

[17] Deng B, Wu Y C, Zhang Y, Yang Y, Li G H. Study of electroless plating process for cobalt-boron alloy and its properties(I)[J]. Electroplating & Finishing, 2001, (1): 12-15.

[18] Yang Y, Wu Y C, Qiao Y, Zhang Y, Deng B, Li G H. Study of electroless plating process for cobalt-boron alloy and its properties(II)[J]. Electroplating & Finishing, 2001, (2): 5-7+21.

[19] Shipley C R. Historical highlights of electroless plating[J]. Plat. Surf. Finish., 1984, 71(6): 92-99.

[20] Li N. Practical technology of electroless plating[M]. China: Chemical Industry Press, 2012: 45.

[21] Saito T, Sato E, Matsuoka M, Iwakura C. Electroless deposition of Ni-B, Co-B and Ni-Co-B alloys using dimet-hylamineborane as a reducing agent[J]. J. Appl. Electro-chem., 1998, 28(5): 559-563.

[22] Shacham-Diamand Y, Sverdlov Y, Bogush V, Ofek-Alomg R. A surface adsorption model for electroless cobalt alloy thin films[J]. J. Solid State Electrochem., 2007, 11(7): 929-938.
doi: 10.1007/s10008-007-0285-5 URL

[23] Stankeviciene I, Jagminiene A, Tamasauskaite-Tamasiunaite L, Sukackiene Z, Gedvilas M, Norkus E. Investigation of electroless deposition of cobalt films by EQCM in the presence of different amines[J]. Mater Sci. Eng. B-Adv. Funct. Solid-State Mater., 2019, 241: 9-12.
doi: 10.1016/j.mseb.2019.02.004 URL

[24] Zyulkov I, Armini S, Opsomer K, Detavernier C, De Gendt S. Selective electroless deposition of cobalt using amino-terminated SAMs[J]. J. Mater. Chem. C, 2019, 7(15): 4392-4402.
doi: 10.1039/c9tc00145j

[25] Chang S Y, Wan C C, Wang Y Y, Shih C H, Tsai M H, Shue S L, Yu C H, Liang M S. Characterization of Pd-free electroless Co-based cap selectively deposited on Cu surface via borane-based reducing agent[J]. Thin Solid Films, 2006, 515(3): 1107-1111.
doi: 10.1016/j.tsf.2006.07.044 URL

[26] Cheng S L, Hsu T L, Lee T, Lee S W, Hu J C, Chen L T. Characterization and kinetic investigation of electroless deposition of pure cobalt thin films on silicon substrates[J]. Appl. Surf. Sci., 2013, 264: 732-736.
doi: 10.1016/j.apsusc.2012.10.111 URL

[27] Yagi S, Kawamori M, Matsubara E. Electrochemical QCM study of the synthesis process of cobalt nanoparticles via electroless deposition[J]. Electrochem. Solid State Lett., 2010, 13(2): E1-E3.
doi: 10.1149/1.3269051 URL

[28] Djokic S S. Electroless deposition of cobalt using hydrazine as a reducing agent[J]. J. Electrochem. Soc., 1997, 144(7): 2358-2363.
doi: 10.1149/1.1837818 URL

[29] Ohno I, Wakabayashi O, Haruyama S. Anodic oxidation of reductants in electroless plating[J]. J. Electrochem. Soc., 1985, 132(10): 2323-2330.
doi: 10.1149/1.2113572 URL

[30] Kim T Y, Lee M H, Byun J, Jeon H, Choe S, Kim J J. Influence of reducing agent on chemical decomposition of bis(3-sulfopropyl) disulfide (SPS) in Cu Plating bath[J]. J. Electrochem. Soc., 2021, 168(3): 032501.
doi: 10.1149/1945-7111/abe727 URL

[31] Lee M H, Kim M J, Kim J J. Competitive adsorption between bromide ions and bis(3-Sulfopropyl)-disulfide for Cu microvia filling[J]. Electrochim. Acta, 2021, 370: 137707.
doi: 10.1016/j.electacta.2020.137707 URL

[32] Shingubara S, Wang Z L, Yaegashi O, Obata R, Sakaue H, Takahagi T. Bottom-up fill of copper in high aspect ratio via holes by electroless plating[C]. Shingubara S, Proceedings of IEEE International Electron Devices Meeting, USA: IEEE, 2003.

[33] Shingubara S, Wang Z L, Yaegashi O, Obata R, Sakaue H, Takahagi T. Bottom-up fill of copper in deep submicrometer holes by electroless plating[J]. Electrochem. Solid State Lett., 2004, 7(6): C78-C80.
doi: 10.1149/1.1707029 URL

[34] Wang Z L, Yaegashi O, Sakaue H, Takahagi T, Shingubara S. Bottom-up fill for submicrometer copper via holes of ULSIs by electroless plating[J]. J. Electrochem. Soc., 2004, 151(12): C781-C785.
doi: 10.1149/1.1810453 URL

[35] Wang Z L, Yaegashi O, Sakaue H, Takahagi T, Shingubara S. Suppression of native oxide growth in sputtered TaN films and its application to Cu electroless plating[J]. J. Appl. Phys., 2003, 94(7): 4697-4701.
doi: 10.1063/1.1609644 URL

[36] Lee C H, Lee S C, Kim J J. Bottom-up filling in Cu electroless deposition using bis-(3-sulfopropyl)-disulfide (SPS)[J]. Electrochim. Acta, 2005, 50(16-17): 3563-3568.
doi: 10.1016/j.electacta.2005.01.009 URL

[37] Hasegawa M, Yamachika N, Shacham-Diamand Y, Okinaka Y, Osaka T. Evidence for “superfilling” of submicrometer trenches with electroless copper deposit[J]. Appl. Phys. Lett., 2007, 90(10): 101916.
doi: 10.1063/1.2712505 URL

[38] Wang X. Bottom-up filling in electroless plating with an addition of JGB-RPE[J]. Russ. J. Electrochem., 2014, 50(5): 438-443.
doi: 10.1134/S1023193514050103 URL

[39] Yang Z F, Li N, Wang X, Wang Z X, Wang Z L. Bottom-up filling in electroless plating with an addition of PEG-PPG triblock copolymers[J]. Electrochem. Solid State Lett., 2010, 13(7): D47-D49.
doi: 10.1149/1.3388488 URL

[40] Wang X, Yang Z F, Wang Z L. Effect of additive triblock copolymer PEP-3100 on bottom-up filling in electroless copper plating[J]. Russ. J. Electrochem., 2012, 48(1): 99-103.
doi: 10.1134/S1023193511120135 URL

[41] Hasegawa M, Okinaka Y, Shachm-Diamand Y, Osaka T. Void-free trench-filling by electroless copper deposition using the combination of accelerating and inhibiting additives[J]. Electrochem. Solid-State Lett., 2006, 9(8): C138-C140.
doi: 10.1149/1.2206008 URL

[42] Hasegawa M, Yamachika N, Okinaka Y, Shacham-Diamand Y, Osaka T. An electrochemical investigation of additive effect in trench-filling of ULSI interconnects by electroless copper deposition[J]. Electrochemistry, 2007, 75(4): 349-358.
doi: 10.5796/electrochemistry.75.349 URL

[43] Wang X, Yang Z F, Li N, Liu Z H, Yang Z P, Wang Z L. First synergy effects of SPS and PEG-4000 on the bottom-up filling in electroless copper plating[J]. J. Electro-chem. Soc., 2010, 157(10): D546-D549.
doi: 10.1149/1.3479191 URL

[44] Yang Z F, Wang X, Li N, Wang Z X, Wang Z L. Design and achievement of a complete bottom-up electroless copper filling for sub-micrometer trenches[J]. Electrochim. Acta, 2011, 56(9): 3317-3321.
doi: 10.1016/j.electacta.2011.01.022 URL

[45] Zan L X, Liu Z H, Yang Z P, Wang Z L. A synergy effect of 2-MBT and PE-3650 on the bottom-up filling in electroless copper plating[J]. Electrochem. Solid-State Lett., 2011, 14(12): D107-D109.
doi: 10.1149/2.018112esl URL

[46] Zan L X, Wang Z L, Liu Z H, Yang Z P. Achievement of bottom-up electroless nickel filling on the SiO2 surface with Pd-activated SAM[J]. ECS Electrochem. Lett., 2013, 2(1): D1-D3.
doi: 10.1149/2.006301eel URL



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