Thermal Atomic Layer Etching of Copper by Sequential Steps Involving Oxidation and Exposure to Hexafluoroacetylacetone

Mohimi, Elham; Chu, Xiaoqing I.; Trinh, Brian B.; Babar, Shaista; Girolami, Gregory S.; Abelson, John R.

doi:10.1149/2.0211809jss

Cited by 37 publications

(34 citation statements)

References 48 publications

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“…Many materials can be etched using thermal ALE . These materials include metal oxides such as Al 2 O 3 , ,, HfO 2 , , ZnO, Ga 2 O 3 , and WO 3 , metal nitrides such as AlN, TiN, and GaN, semiconductor materials such as Si, SiO 2 , and Si 3 N 4 , and metals such as W, Cu, and Co . Thermal ALE will be critical to provide atomic layer precision for etching to fabricate advanced three-dimensional semiconductor devices …”

Section: Introductionmentioning

confidence: 99%

Spontaneous Etching of Metal Fluorides Using Ligand-Exchange Reactions: Landscape Revealed by Mass Spectrometry

et al. 2021

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Thermal atomic layer etching (ALE) can be performed using sequential reactions based on surface modification followed by volatile release of the modified surface layer. Surface modification can be accomplished using fluorination. Volatile release can then be achieved using precursors that undergo ligand-exchange reactions with the fluorinated surface layer. Metal fluorides can be employed to model the fluorinated surface layer. The ligand-exchange reaction between the precursor and the metal fluoride can lead to spontaneous etching of the metal fluoride. A new reactor with in situ quadrupole mass spectrometry (QMS) was constructed to observe the volatile etch products from the reaction of ligand-exchange precursors with metal fluoride powders. The metal fluoride powders were AlF3, HfF4, GaF3, InF3, and SnF4. The ligand-exchange precursors were Al(CH3)3, SiCl4, and TiCl4. A variety of studies were conducted including Al(CH3)3 + AlF3, SiCl4 + HfF4, SiCl4 + InF3, TiCl4 + SnF4, Al(CH3)3 + GaF3, and SiCl4 + AlF3. The temperature-dependent in situ QMS studies revealed the many possibilities that occur during the ligand-exchange reaction of precursors with metal fluoride powders. Various categories of behavior were observed from these studies: (i) Ligand exchange occurs at low temperature, but metal etch products from the substrate are not observed until high temperature. (ii) Ligand-exchange and metal etch products from the substrate are observed at similar temperatures. (iii) Ligand exchange occurs, but no metal etch products from the substrate are observed up to a limiting temperature. Knowledge of these possibilities for the ligand-exchange reaction between precursors and metal fluoride powders during spontaneous etching helps to further the understanding of thermal ALE.

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Section: Introductionmentioning

confidence: 99%

Spontaneous Etching of Metal Fluorides Using Ligand-Exchange Reactions: Landscape Revealed by Mass Spectrometry

et al. 2021

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“…One key group of materials that has not received as much attention is elemental metals. There has been previous work on W, Cu, and Co thermal ALE. ,− However, there are not general guidelines on procedures to volatilize metal complexes originating from elemental metals. Thermal metal ALE is particularly challenging because the oxidation state of the initial elemental metal must be changed to match the oxidation state of the volatile metal etch product.…”

Section: Introductionmentioning

confidence: 99%

Thermal Atomic Layer Etching of Nickel Using Sequential Chlorination and Ligand-Addition Reactions

2021

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The thermal atomic layer etching (ALE) of nickel was demonstrated using sequential chlorination and ligand-addition reactions. Nickel chlorination was achieved using SO2Cl2 (sulfuryl chloride) as the chlorine reactant. PMe3 (trimethylphosphine) was employed as the ligand-addition reactant. Sequential exposures of SO2Cl2 and PMe3 led to Ni thermal ALE. This procedure was inspired by the covalent bond classification (CBC) method that categorizes the most common compounds of various metals. Based on the CBC method, the surface reactions during thermal Ni ALE were performed to form NiX2L2 products, where Cl is the X ligand and PMe3 is the L ligand. Using this strategy, thermal Ni ALE was observed at temperatures from 75–200 °C. The etch rates were determined from in situ quartz crystal microbalance (QCM) measurements. The average etch rates determined from the mass changes were 0.14 ± 0.13, 0.57 ± 0.36, 0.67 ± 0.45, 1.30 ± 0.68, and 3.07 ± 1.56 Å/cycle for the temperatures 75, 100, 125, 150, and 175 °C, respectively. The QCM investigations revealed that there was a mass increase on every SO2Cl2 exposure and a mass loss on every PMe3 exposure, resulting in a net mass loss. The amount of chlorination for a given SO2Cl2 exposure increased with increasing temperature. The amount of mass lost on each PMe3 exposure also increased with increasing temperature. The etch rates were also confirmed using ex situ X-ray reflectivity measurements on Ni films on silicon wafers. The etch rates varied from 0.39 ± 0.10 Å/cycle at 125 °C to 2.16 ± 0.47 Å/cycle at 200 °C. Mass spectrometry analysis revealed that the volatile etch product was NiCl2(PMe3)2 as expected from the CBC method. In addition, scanning electron microscopy revealed that the nickel surface morphology had negligible changes after ALE. Atomic force microscopy analysis showed that thin nickel films remained smooth during initial etching and may experience some slight roughening with progressive etching. Using the CBC method to create novel thermal ALE procedures can be generalized for the thermal ALE of many different metals.

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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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Thermal Atomic Layer Etching of Copper by Sequential Steps Involving Oxidation and Exposure to Hexafluoroacetylacetone

Cited by 37 publications

References 48 publications

Spontaneous Etching of Metal Fluorides Using Ligand-Exchange Reactions: Landscape Revealed by Mass Spectrometry

Spontaneous Etching of Metal Fluorides Using Ligand-Exchange Reactions: Landscape Revealed by Mass Spectrometry

Thermal Atomic Layer Etching of Nickel Using Sequential Chlorination and Ligand-Addition Reactions

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

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