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Cobalt Metal ALD: Understanding the Mechanism and Role of Zink Alkyl Precursors as Reductants for Low Resistivity Co Thin Films

submitted on 12.03.2021, 06:50 and posted on 16.03.2021, 11:05 by David Zanders, Ji Liu, Jorit Obenlüneschloß, Claudia Bock, Detlef Rogalla, Lukas Mai, Michael Nolan, Sean Barry, Anjana Devi
In this work, we report a new and promising approach towards the atomic layer deposition (ALD) of metallic Co thin films. Utilizing the simple and known CoCl2(TMEDA) (TMEDA = N,N,N’,N’-tetramethylethylenediamine) precursor in combination with the intramolecularly stabilized Zn aminoalkyl compound Zn(DMP)2 (DMP = dimethylaminopropyl) as auxiliary reducing agent, a thermal ALD process is developed that enables the deposition of Zn free Co thin films. ALD studies demonstrate the saturation behavior of both precursors, linearity in dependency of the applied number of cycles as well as investigations of the temperature dependency of film growth in a regime of 140 - 215 °C. While the process optimization is carried out on Si with native oxide, additional growth studies are conducted on Au and Pt substrates. This study is complemented by initial reactivity and suitability tests of several potential Zn alkyl reducing agents. For the CoCl2(TMEDA) - Zn(DMP)2 combination, these findings allow to propose a series of elemental reaction steps hypothetically leading to pure Co film formation in the ALD process whose feasibility are probed by a set of DFT calculations. The DFT results show that for reactions of the precursors in the gas phase and on Co(111) substrate surfaces, a pathway involving C-C coupling and diamine formation through reductive elimination of an intermediate Co(II) alkyl species is preferred. Co thin films with an average thickness of 10 - 25 nm obtained from the process are subjected to thorough analysis comprising AFM, SEM, RBS/NRA as well as depth profiling XPS. Resistivity measurements for ~ 22 nm thick films grown on a defined SiO2 insulator layer yield highly promising values in a range of 15 - 20 μΩ cm without any after treatment.


Central tasks of the SFB/Transregio 87 (Z)

Deutsche Forschungsgemeinschaft

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Collaborative project: Research into new, flexible sensor systems based on two-dimensional material systems - ForMikro-FlexTMDSense -, sub-project: Research into new process technologies for flexible pH sensor systems based on two-dimensional materials

Federal Ministry of Education and Research

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Process development and mechanistic investigation of barrier materials for advanced interconnect technology

Science Foundation Ireland

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Email Address of Submitting Author


Ruhr University Bochum



ORCID For Submitting Author


Declaration of Conflict of Interest

No conflict of interest