Thermal Atomic Layer Etching of Aluminum Oxide (Al2O3) Using Sequential Exposures of Niobium Pentafluoride (NbF5) and Carbon Tetrachloride (CCl4): A Combined Experimental and Density Functional Theory Study of the Etch Mechanism

Sharma, Varun; Elliott, Simon D.; Blomberg, Tom; Haukka, Suvi; Givens, M. E.; Tuominen, M.; Ritala, Mikko

doi:10.1021/acs.chemmater.1c00142

Cited by 11 publications

(7 citation statements)

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“…5 Other approaches for thermal Al 2 O 3 ALE include NbF 5 for fluorination and CCl 4 for ligand exchange. 33 Hybrid plasma/ thermal Al 2 O 3 ALE processes have also been defined using SF 6 plasma for fluorination and Al(CH 3 ) 3 for ligand exchange. 34 Although all the ligand-exchange precursors for thermal Al 2 O 3 ALE discussed above may etch Al 2 O 3 , they may not all etch other materials.…”

Section: Atomic Layer Etching (Ale) Is a Technique That Can Removementioning

confidence: 99%

“…Two prominent ligand-exchange precursors have been Al(CH 3 ) 3 and AlCl(CH 3 ) 2 . ,− Mass spectrometry studies have identified the main ligand-exchange products from the Al(CH 3 ) 3 reactant as AlF(CH 3 ) 2 with either itself or Al(CH 3 ) 3 in dimers or trimers. , Thermal Al 2 O 3 ALE has also been developed using SF 4 for fluorination and Sn(acac) 2 for ligand exchange . Other approaches for thermal Al 2 O 3 ALE include NbF 5 for fluorination and CCl 4 for ligand exchange . Hybrid plasma/thermal Al 2 O 3 ALE processes have also been defined using SF 6 plasma for fluorination and Al(CH 3 ) 3 for ligand exchange …”

Section: Introductionmentioning

confidence: 99%

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Thermal Atomic Layer Etching of Al₂O₃ Using Sequential HF and BCl₃ Exposures: Evidence for Combined Ligand-Exchange and Conversion Mechanisms

2022

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The atomic layer etching (ALE) of Al2O3 was demonstrated using sequential HF and BCl3 exposures. BCl3 is a new precursor for thermal Al2O3 ALE that can provide pathways for both ligand-exchange and conversion etching mechanisms. Fourier transfer infrared (FTIR) spectroscopy was utilized to observe the growth of Al2O3 ALD films using Al(CH3)3 (trimethylaluminum) and H2O and the subsequent etching of the Al2O3 ALD films using HF and BCl3. To confirm the conversion reaction, FTIR difference spectra revealed that initial BCl3 exposures on the Al2O3 ALD film converted the Al2O3 surface to a B2O3 layer. Surprisingly, larger BCl3 exposures on the B2O3 layer could also etch the B2O3 layer. Quadrupole mass spectrometry (QMS) measurements revealed that BCl3 produced ion intensities for AlCl3 + from AlCl3 during the conversion of the Al2O3 surface to a B2O3 layer. Concurrently, the BCl3 also etched the converted B2O3 layer and ion intensities for B3O3Cl3 + were observed from B3O3Cl3 boroxine rings. After the conversion of the Al2O3 surface to a B2O3 layer, the initial HF exposure then removed the B2O3 layer and fluorinated the underlying Al2O3 film. Following the initial BCl3 and HF exposures, the FTIR difference spectra showed that Al2O3 ALE proceeded primarily by a reaction pathway where HF fluorinates the Al2O3 and then BCl3 removes the surface fluoride layer by a ligand-exchange reaction. However, there was still evidence for some conversion of Al2O3 to a B2O3 layer during the subsequent BCl3 exposures and then removal of the B2O3 layer by the HF exposures. Spectroscopic ellipsometry measurements determined the etch rates during thermal Al2O3 ALE during sequential HF and BCl3 exposures. The etch rates were 0.03, 0.31, 0.65, and 0.92 Å/cycle at temperatures of 230, 255, 280, and 290 °C, respectively. QMS analysis also investigated the volatile etch products during the sequential HF and BCl3 exposures on Al2O3 at 270 °C. During the BCl3 exposures after the initial cycle, the QMS measurements observed ion intensities for BFCl2 + and AlCl2 +. BFCl2 was the major ligand-exchange product, and AlCl3 was the main metal chloride etching product. In addition, small ion intensities for B3O3Cl3 + were also present from the conversion of Al2O3 to B2O3 and subsequent etching of B2O3 by BCl3 to yield boroxine ring products. These results indicate that thermal Al2O3 ALE using sequential HF and BCl3 exposures occurs by combined ligand-exchange and conversion mechanisms.

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Section: Atomic Layer Etching (Ale) Is a Technique That Can Removementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Thermal Atomic Layer Etching of Al₂O₃ Using Sequential HF and BCl₃ Exposures: Evidence for Combined Ligand-Exchange and Conversion Mechanisms

2022

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“…17,18 Thermal ALE of amorphous Al 2 O 3 has also been reported using NbF 5 to replace hydrogen fluoride (HF) as the fluorination agent and CCl 4 for the halide-exchange reaction. 19 Thermal ALE can also be performed by other processes such as conversion, 20 oxidation, 21 oxidation/chlorination, 22 and chlorinefluorine ligand exchange. 23 Plasma ALE consists of two halfreactions of surface adsorption and surface removal where Ar plasma bombardment is used for etching in the surface removal step.…”

Section: Introductionmentioning

confidence: 99%

Origin of enhanced thermal atomic layer etching of amorphous HfO2

Mullins

Moreno

Nolan

2022

Journal of Vacuum Science &Amp; Technology A

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HfO2 is a high- k material that is used in semiconductor devices. Atomic-level control of material processing is required for the fabrication of thin films of high- k materials at nanoscale device sizes. Thermal atomic layer etching (ALE) of metal oxides, in which up to one monolayer of material can be removed, can be achieved by sequential self-limiting fluorination and ligand-exchange reactions at elevated temperatures. First-principles-based atomic-level simulations using density functional theory can give deep insights into the precursor chemistry and the reactions that drive the etching of metal oxides. A previous study examined the hydrogen fluoride (HF) pulse in the first step in the thermal ALE process of crystalline HfO2 and ZrO2. This study examines the HF pulse on amorphous HfO2 using first-principles simulations. The Natarajan–Elliott analysis, a thermodynamic methodology, is used to compare reaction models representing the self-limiting and spontaneous etch processes taking place during an ALE pulse. For the HF pulse on amorphous HfO2, we found that thermodynamic barriers impeding spontaneous etching are present at ALE relevant temperatures. HF adsorption calculations on the amorphous oxide surface are studied to understand the mechanistic details of the HF pulse. An HF molecule adsorbs dissociatively by forming Hf–F and O–H bonds. HF coverages ranging from 1.1 ± 0.3 to 18.0 ± 0.3 HF/nm2 are investigated, and a mixture of molecularly and dissociatively adsorbed HF molecules is present at higher coverages. A theoretical etch rate of −0.82 ± 0.02 Å/cycle for amorphous HfO2 was calculated using a maximum coverage of 9.0 ± 0.3 Hf–F/nm2. This theoretical etch rate is greater than the theoretical etch rate for crystalline HfO2 that we previously calculated at −0.61 ± 0.02 Å/cycle. Undercoordinated atoms and void regions in amorphous HfO2 allow for more binding sites during fluorination, whereas crystalline HfO2 has a limited number of adsorption sites.

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“…One such model, the Natarajan−Elliott analysis 12 (N−E analysis), provides great insight into the temperature dependence of the thermal ALE fluorination step. While it already improves on the previous work by supplementing the bulk reactions (converting bulk metal to bulk oxides and halides) with surface models at different coverages, the crystal termination and the coverages are chosen arbitrarily.…”

Section: Introductionmentioning

confidence: 99%

“…These challenges also mean that the mechanisms lack atomistic detail, limiting their usefulness in understanding the chemistry and conditions that lead to a successful metal ALE process. For this purpose, a computational thermodynamic model of ALE is necessary.One such model, the Natarajan−Elliott analysis12 (N−E analysis), provides great insight into the temperature dependence of the thermal ALE fluorination step. While it already improves on the previous work by supplementing the bulk reactions (converting bulk metal to bulk oxides and halides) with surface models at different coverages, the crystal termination and the coverages are chosen arbitrarily.…”

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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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Thermal Atomic Layer Etching of Aluminum Oxide (Al₂O₃) Using Sequential Exposures of Niobium Pentafluoride (NbF₅) and Carbon Tetrachloride (CCl₄): A Combined Experimental and Density Functional Theory Study of the Etch Mechanism

Cited by 11 publications

References 54 publications

Thermal Atomic Layer Etching of Al₂O₃ Using Sequential HF and BCl₃ Exposures: Evidence for Combined Ligand-Exchange and Conversion Mechanisms

Thermal Atomic Layer Etching of Al₂O₃ Using Sequential HF and BCl₃ Exposures: Evidence for Combined Ligand-Exchange and Conversion Mechanisms

Origin of enhanced thermal atomic layer etching of amorphous HfO2

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

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Thermal Atomic Layer Etching of Aluminum Oxide (Al2O3) Using Sequential Exposures of Niobium Pentafluoride (NbF5) and Carbon Tetrachloride (CCl4): A Combined Experimental and Density Functional Theory Study of the Etch Mechanism

Cited by 11 publications

References 54 publications

Thermal Atomic Layer Etching of Al2O3 Using Sequential HF and BCl3 Exposures: Evidence for Combined Ligand-Exchange and Conversion Mechanisms

Thermal Atomic Layer Etching of Al2O3 Using Sequential HF and BCl3 Exposures: Evidence for Combined Ligand-Exchange and Conversion Mechanisms

Origin of enhanced thermal atomic layer etching of amorphous HfO2

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

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Product

Resources

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Thermal Atomic Layer Etching of Aluminum Oxide (Al₂O₃) Using Sequential Exposures of Niobium Pentafluoride (NbF₅) and Carbon Tetrachloride (CCl₄): A Combined Experimental and Density Functional Theory Study of the Etch Mechanism

Thermal Atomic Layer Etching of Al₂O₃ Using Sequential HF and BCl₃ Exposures: Evidence for Combined Ligand-Exchange and Conversion Mechanisms

Thermal Atomic Layer Etching of Al₂O₃ Using Sequential HF and BCl₃ Exposures: Evidence for Combined Ligand-Exchange and Conversion Mechanisms