Review Article: Plasma–surface interactions at the atomic scale for patterning metals

Altieri, Nicholas D.; Chen, Jack Kun-Chieh; Minardi, Luke; Chang, Jane P.

doi:10.1116/1.4993602

Cited by 35 publications

(25 citation statements)

References 62 publications

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“…Computational methods based on density functional theory (DFT), with at least gradient-corrected exchange-correlation functionals, now routinely provide atomic-scale understanding of many ground-state chemical reactions and materials properties. − DFT-based simulations have been instrumental to innovations in the fields of photovoltaics, − (photo)electrocatalysis, − energy storage devices, , and materials (bulk and surface) processing − to name a few. It has become an enabling approach for functional material design and chemical process development and has been used to evaluate gas-phase chemical processes relevant to the semiconductor industry, including chemical vapor deposition (CVD) and ALD of copper. , More recently, DFT has provided understanding of surface reactions during ALE of aluminum oxide and polymers. , While ALE of copper has been reported recently experimentally, − quantification of the volatile reaction products has been challenging due to their low concentrations. It is therefore the goal of this work to combine experimental studies and theoretical insight to delineate the most probable reaction mechanism leading to selective ALE of copper.…”

Section: Introductionmentioning

confidence: 99%

Precise Control of Nanoscale Cu Etching via Gas-Phase Oxidation and Chemical Complexation

et al. 2021

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We present a cyclic process for selective and anisotropic atomic layer etching of copper: an oxygen plasma modulates the depth and directionality of the oxidized layer, while formic acid vapor selectively removes the copper oxide scale from the metallic copper. Via density functional theory, with finite temperature and pressure free energy corrections, we evaluate the feasibility of formation of gas-phase Cu(II) and Cu(I) complexes with formate, water, formic acid, and combinations thereof as ligands. These complexes result from the neutralization reaction between copper oxide (CuO and Cu2O) and formic acid, with and without water. We identified and evaluated the formation free energies of formato, formic acid, aquahydroxo, and aquaformato complexes of Cu(II) and Cu(I). Under relevant experimental pressures, we find the water-free dimeric tetra(μ-formato)dicopper(II) “paddlewheel” complex (Cu2(HCOO)4) to be the most favorable etching product, with its formation reaching equilibrium conditions from CuO. The most likely precursor for the dimer is the diformatodi(formic acid)copper(II) monomer, which favorably dimerizes under the same water-lean condition at which the dimer persists. Stabilization of gas-phase Cu (oxide) derivatives thus can be achieved through complexation, enabling gas-phase etching of Cu. This work provides complementary experimental and theoretical studies that illuminate the nature of highly controlled etching with formic acid of nanoscopic CuO(s) layers covering Cu nanoarchitectures, which is relevant for the fabrication of next-generation integrated circuits.

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Section: Introductionmentioning

confidence: 99%

Precise Control of Nanoscale Cu Etching via Gas-Phase Oxidation and Chemical Complexation

et al. 2021

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“…Recently, Altieri et al published a paper that summarizes different plasma mixture interactions with different metals, especially Cu but also Co, F e or T iN materials [18]. Other research works dealt with the etching of steel and metal alloys [19,20].…”

Section: Literature Overviewmentioning

confidence: 99%

Etching of iron and iron–chromium alloys using ICP-RIE chlorine plasma

Dain¹,

Laourine²,

Guilet³

et al. 2021

Plasma Sources Sci. Technol.

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The dry etching process of Fe, Cr and Fe-Cr alloys under a chlorine-based plasma is studied. The objective is to create new surface functionalities. The approach combines an experimental study of an ICP (Inductively Coupled Plasma) reactor with the development of a multi-scale etching model including kinetic, sheath and surface models. The results from plasma etching of substrates made of Fe, Cr and Fe-Cr alloys are presented. Optical emission spectroscopy and interferometry measurements show strong modifications of the plasma when Fe or Cr samples are present in the reactor. It is shown that Fe is easier to etch than Cr. The study highlights the role of chemical etching by the formation of volatile products such as FeCl 3 . The Cr content in Fe-Cr alloys has a strong impact on both the lateral and vertical etch rates, as well as on the roughness along the profile. For Fe-Cr alloys, the experimental and calculated values of etch rate are very similar. The concept of hard zones is introduced to get a better agreement between simulation results and experimental ones. This good agreement demonstrates the capability of the developed simulator to implement new phenomena.

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“…Recently, a novel process combining plasma activation and thermal removal was developed and successfully applied to directionally etch Ni 4,5 and Cu. 6 This process is illustrated in with organic etchants that react with the surface oxide to form volatile complexes and water, eliminating the need for an extra energy source and avoiding redeposition. This new process, termed plasma-thermal ALE, is conceptually very similar to the thermal ALE process developed by George and co-workers.…”

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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Review Article: Plasma–surface interactions at the atomic scale for patterning metals

Cited by 35 publications

References 62 publications

Precise Control of Nanoscale Cu Etching via Gas-Phase Oxidation and Chemical Complexation

Precise Control of Nanoscale Cu Etching via Gas-Phase Oxidation and Chemical Complexation

Etching of iron and iron–chromium alloys using ICP-RIE chlorine plasma

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

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