Stability of hexafluoroacetylacetone molecules on metallic and oxidized nickel surfaces in atomic-layer-etching processes

Basher, Abdulrahman H.; Krstić, Marjan; Takeuchi, Takae; Isobe, Michiro; Ito, Tomoko; Kiuchi, Masato; Karahashi, Kazuhiro; Wenzel, Wolfgang; Hamaguchi, Satoshi

doi:10.1116/1.5127532

Cited by 10 publications

(9 citation statements)

References 23 publications

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“…This observation leads us to think that there may be a disconnect between the numerous current computational investigations of the ALE process and the realistic processing conditions. The majority of the computational studies of the diketonate ligands participating in the metal ALE start with the most thermodynamically stable bidentate structure ,, and find it thermodynamically impossible at reasonable processing conditions to form a metal-containing product that could be removed from the terrace site of the surface. However, in realistic processing conditions, at reasonably high pressures, the kinetic factors and surface crowding by the ligands could easily lead to the formation of stable monodentate diketonate ligands as dominant surface species (even if there is a presence of stable bidentate ligands) that could fundamentally change the energy landscape for analysis of ALE schemes.…”

Section: Results and Discussionmentioning

confidence: 99%

Molecular Mechanism of Thermal Dry Etching of Iron in a Two-Step Atomic Layer Etching Process: Chlorination Followed by Exposure to Acetylacetone

2021

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Controlling thickness and morphology of transition-metal thin films used in magnetic random-access memory fabrication is a major challenge. Thermal dry etching has emerged as a method of choice for preparing the desired films; however, the mechanisms of the underlying surface processes are very difficult to assess. In this work, thermal dry etching of metallic iron by using sequential exposure to chlorine gas and 2,4-pentanedione (acetylacetone, acacH) was investigated. The mechanism of reacting acacH with chlorine-modified iron surface was studied by following the fragments desorbing from the surface in temperature-programmed desorption experiments in half-cycle processes that compared the chlorinated, oxidized, mixed (Cl and O), and clean (sputtered) iron films. In situ Auger electron spectroscopy and ex situ X-ray photoelectron spectroscopy of each sample after each etching step confirmed that the surface is activated by chlorine and then the chlorine-containing iron species are removed from the top layer of the sample, resulting in a metallic iron surface. No etching of clean (sputtered) surface was observed with acacH. The complete mechanism of acacH reaction with chlorinated iron samples is complicated, and etch products can contain both Fe2+ and Fe3+. However, a number of major conclusions, including the formation of surface intermediates and the final products of etching, primarily removal of Fe(acac) x Cl y , are inferred by comparing the results of these experiments with the computational investigation of selected surface processes using density functional theory calculations.

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Section: Results and Discussionmentioning

confidence: 99%

Molecular Mechanism of Thermal Dry Etching of Iron in a Two-Step Atomic Layer Etching Process: Chlorination Followed by Exposure to Acetylacetone

2021

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“…9,35,[65][66][67] Thermal ALE, which uses thermal chemical reactions, rather than ion irradiation, in the desorption step, can avoid surface damage induced by ion impact. 12,[68][69][70][71][72][73][74] On the other hand, thermal ALE processes typically lead to isotropic etch, i.e. etching that proceeds in the surface normal direction.…”

Section: Introductionmentioning

confidence: 99%

Five-step plasma-enhanced atomic layer etching of silicon nitride with a stable etched amount per cycle

Hirata

Fukasawa

Tercero

et al. 2022

Jpn. J. Appl. Phys.

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Atomic layer etching is an advanced plasma etching technique that enables the atomic-precision control. In this study, the effects of surface conditions on the stability of the etched amount per cycle (EPC) in silicon nitride (SiN) plasma-enhanced atomic layer etching (PE-ALE) were examined. A single cycle of SiN PE-ALE consisted of two steps: hydrofluorocarbon (HFC) absorption step and argon-ion (Ar+) desorption step. After a few cycles, an etch-stop of SiN occurred due to the HFC deposition. An oxygen-plasma ashing step was introduced after desorption step, which made three-step SiN PE-ALE. The etch-stop was avoided but the EPC was low due to the surface oxidation of SiN. By combining this three-step SiN PE-ALE with subsequent two-step SiO2 PE-ALE, which consists of fluorocarbon adsorption step and Ar+ desorption step, SiN PE-ALE was achieved with a stable and large EPC. This five-step SiN PE-ALE allows the precise control of SiN etched depth.

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“…While we do not expect kinetic barriers to be significant in the activation step, in the removal step, the formation of the hydride and desorption of the formed complex might be activated. 13,14 Existing data suggests that the desorption of the metal−organic complex is the limiting step and often high temperature is required to overcome the barrier. 7 It is likely, however, that the magnitude of such barriers will depend to a significant extent on the surface morphology.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamics of Atomic Layer Etching Chemistry on Copper and Nickel Surfaces from First Principles

Xia

Sautet

2021

Chem. Mater.

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Plasma-thermal atomic layer etching is a promising technique to enable selective and directional etching on metals. It involves a plasma activation step and a thermal step where etchant molecules remove a fraction of the surface. To accelerate process development, a computational model for the thermodynamics of the thermal removal step is highly desirable. An energy expression is developed here to calculate the removal step energy for an activated slab structure. The approach samples the configurations of the activated metal surfaces and determines the thermodynamic balance of the removal step for each obtained configuration. The heterogeneity of the surface terminations is treated by the equilibrium crystal shape method. The models are put to test with combinations of two modifiers (O & N), two substrates (Cu & Ni) and two etchants (formic acid and formamidine). It is found that higher coverages of modifiers leads to more favorable etching. In addition, our results show that removal step energies vary 1 among different terminations, with differences on the order of 0.5 eV. This suggests etching can preferentially occur over certain crystal terminations. Qualitative agreement with the experiment on the Ni/O/formic acid system is obtained with the layer model at high coverages of oxygen atoms.

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Stability of hexafluoroacetylacetone molecules on metallic and oxidized nickel surfaces in atomic-layer-etching processes

Cited by 10 publications

References 23 publications

Molecular Mechanism of Thermal Dry Etching of Iron in a Two-Step Atomic Layer Etching Process: Chlorination Followed by Exposure to Acetylacetone

Molecular Mechanism of Thermal Dry Etching of Iron in a Two-Step Atomic Layer Etching Process: Chlorination Followed by Exposure to Acetylacetone

Five-step plasma-enhanced atomic layer etching of silicon nitride with a stable etched amount per cycle

Thermodynamics of Atomic Layer Etching Chemistry on Copper and Nickel Surfaces from First Principles

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