Atomic layer deposition of cobalt oxide on oxide substrates and low temperature reduction to form ultrathin cobalt metal films

Zhang, Zizhuo; Nallan, Himamshu C.; Coffey, Brennan M.; Ngo, Thong Q.; Pramanik, Tanmoy; Banerjee, S.; Ekerdt, John G.

doi:10.1116/1.5063669

Cited by 13 publications

(11 citation statements)

References 65 publications

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“…Any surface oxide present was removed by exposing the films to H 2 plasma (0.1 mbar, 100 Watt) for 5 min. As cobalt oxide is easily reduced to pure Co metal by hydrogen plasma, 38 it is assumed that, after H 2 plasma, the sample surface is effectively oxygen-free. Plasma nitriding was performed using the same power and pressure used during the plasma exposure step of the ALD process described previously (i.e., 100 Watt, 1.0 × 10 −2 mbar) at a sample temperature of 100 °C for 1 h. Afterward, the reactor was evacuated for 10 min to allow for the removal of plasma byproducts.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

Plasma-Enhanced Atomic Layer Deposition of Cobalt and Cobalt Nitride: What Controls the Incorporation of Nitrogen?

et al. 2020

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The present study covers the processes that govern the incorporation of nitrogen in the film during atomic layer deposition (ALD) of cobalt and cobalt nitride prepared from cobaltocene (CoCp 2 ) and NH 3 plasma. It is demonstrated that nitrogen incorporation is strongly temperature-dependent; at temperatures of 260 °C and below, the deposited films consist primarily of Co 2 N, whereas increasing the temperature to 300 °C leads to a mixture of Co 3 N and Co, and at 350 °C, nominally pure Co is obtained. The sample temperature clearly has a very strong effect on the composition of the deposited film, and in order to understand this temperature dependence, the thermal stability of the CoN x species formed during the interaction between a sample consisting of pure Co and an NH 3 plasma is analyzed. X-ray photoemission spectroscopy depth profiling reveals that this plasma treatment converts the top 4 nm of the Co film into CoN x . Temperature-programmed desorption experiments show that this nitride layer starts to decompose at a temperature of approximately 290 °C, which eventually leads to complete removal of all nitrogen from the film. Based on this, a reaction scheme for ALD of Co is proposed; the interaction between the NH 3 plasma and the adsorbed CoCp 2 -derived species leads to the formation of cobalt nitride. At temperatures below 290 °C, the resulting film primarily consists of Co 2 N, whereas at 300 °C, partial decomposition takes place, resulting in the formation of a mixture of Co 3 N and pure Co. At 350 °C, decomposition is effectively complete, leading to pure Co with nitrogen contents below 4 at %. Finally, it is argued that the aforementioned mechanism could potentially play a role in plasma-enhanced ALD of other elements that form metastable nitrides such as Ni, Cu, Re, and Ru.

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Section: ■ Experimental Sectionmentioning

confidence: 99%

Plasma-Enhanced Atomic Layer Deposition of Cobalt and Cobalt Nitride: What Controls the Incorporation of Nitrogen?

et al. 2020

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“…Notably, Co had a metallic, zero oxidation state even in the immanent surface region as demonstrated by the stacked Co 2p core level spectra (Figure b). While the Co 2p 3/2 signal was slightly shifted to a higher binding energy for the as-introduced surface, its position was located at or in close proximity to 778.2 eV which is characteristic for the zero-valent state of Co. − The O 1s core level measurements, shown alongside the C 1s, N 1s, and Cl 2p spectra in Figure S17, revealed the presence of only organic oxygen species with a binding energy of 532.7 eV on the surface, likely bonded to the adventitious carbon (for more detailed discussion, see Section 11 of the Supporting Information). Most importantly, high-resolution scans of the entire Zn 2p core level region (1010–1060 eV, Figure c) demonstrated the absence of detectable Zn traces within the Co thin films.…”

Section: Results and Discussionmentioning

confidence: 99%

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

et al. 2021

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In this work, we report a new and promising approach toward 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 an 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 and linearity depending on the applied number of cycles as well as 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 us to propose a series of elemental reaction steps hypothetically leading to pure Co film formation in the ALD process whose feasibility is probed by a set of density functional theory (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 atomic force microscopy, scanning electron microscopy, and Rutherford backscattering spectrometry/nuclear reaction analysis as well as depth profiling X-ray photoemission spectroscopy (XPS). From XPS analysis, it was found that graphitic and carbidic carbon coexist in the Co metal film bulk. Despite carbon concentrations of ∼20 at. % in the Co thin film bulk, 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 postgrowth treatment.

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“…Notably, Co had a metallic, zero oxidation state even in the immanent surface region as demonstrated by the stacked Co 2p core level spectra (Figure 8 b). While the Co 2p3/2 signal was slightly shifted to a higher binding energy for the as-introduced surface, its position was located at or in close proximity to 778.2 eV which is characteristic for the zerovalent state of Co. [54][55][56] The O 1s core level measurements, shown alongside C 1s, N 1s and Cl 2p spectra in Figure S 17, revealed the presence of only organic oxygen species with a binding energy of 532.7 eV on the surface, 57 likely bonded to the adventitious carbon (for more detailed discussion see Section 11 of the SI). Most importantly, high resolution scans of the entire Zn 2p core level region (1010 -1060 eV, Figure 8 c), demonstrated the absence of detectable Zn traces within the Co thin films.…”

Section: Thin Film Analysismentioning

confidence: 99%

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

Zanders

Liu²,

Obenlüneschloß³

et al. 2021

Preprint

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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.

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Atomic layer deposition of cobalt oxide on oxide substrates and low temperature reduction to form ultrathin cobalt metal films

Cited by 13 publications

References 65 publications

Plasma-Enhanced Atomic Layer Deposition of Cobalt and Cobalt Nitride: What Controls the Incorporation of Nitrogen?

Plasma-Enhanced Atomic Layer Deposition of Cobalt and Cobalt Nitride: What Controls the Incorporation of Nitrogen?

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

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

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