Prospects for Thermal Atomic Layer Etching Using Sequential, Self-Limiting Fluorination and Ligand-Exchange Reactions

ACS Nano ◽  
2016 ◽  
Vol 10 (5) ◽  
pp. 4889-4894 ◽  
Author(s):  
Steven M. George ◽  
Younghee Lee
Keyword(s):  
Ligand Exchange ◽  
Atomic Layer ◽  
Exchange Reactions ◽  
Atomic Layer Etching

A first-principles study of the atomic layer deposition of ZnO on carboxyl functionalized carbon nanotubes: the role of water molecules

2021 ◽  
Vol 23 (5) ◽  
pp. 3467-3478
Author(s):  
J. I. Paez-Ornelas ◽  
H. N. Fernández-Escamilla ◽  
H. A. Borbón-Nuñez ◽  
H. Tiznado ◽  
Noboru Takeuchi ◽  
...  
Keyword(s):  
First Principles ◽  
Ligand Exchange ◽  
Functional Group ◽  
Atomic Layer ◽  
High Reactivity ◽  
Water Molecules ◽  
Exchange Reactions ◽  
Layer Deposition ◽  
The Right

Atomic description of ALD in systems that combine large surface area and high reactivity is key for selecting the right functional group to enhance the ligand-exchange reactions.

Mechanism of the HF Pulse in the Thermal Atomic Layer Etch of HfO2 and ZrO2: A First Principles Study

2019 ◽  
Author(s):  
Rita Mullins ◽  
Suresh Natarajan ◽  
Simon D. Elliott ◽  
Michael Nolan
Keyword(s):  
First Principles ◽  
Ligand Exchange ◽  
Elevated Temperatures ◽  
Atomic Layer ◽  
Level Control ◽  
Exchange Reactions ◽  
Nanoscale Device ◽  
High K ◽  
Reaction Models ◽  
High K Materials

<div>HfO2 and ZrO2 are two high-k materials that are important in the down-scaling of semiconductor devices. Atomic level control of material processing is required for fabrication of thin films of these materials at nanoscale device sizes. Thermal Atomic Layer Etch (ALE) of metal oxides, in which up to one monolayer of the material can be removed, can be achieved by sequential self-limiting fluorination and ligand-exchange reactions at elevated temperatures. However, to date a detailed atomistic understanding of the mechanism of thermal ALE of these technologically important oxides is lacking. In this paper, we investigate the hydrogen fluoride pulse in the first step in the thermal ALE process of HfO2 and ZrO2 using first principles simulations. We introduce Natarajan-Elliott analysis, a thermodynamic methodology, to compare reaction models representing the self-limiting (SL) and continuous spontaneous etch (SE) processes taking place during an ALE pulse. Applying this method to the first HF pulse on HfO2 and ZrO2 we found that thermodynamic barriers impeding continuous etch are present at ALE relevant temperatures. We performed explicit HF adsorption calculations on the oxide surfaces to understand the mechanistic details of the HF pulse. A HF molecule adsorbs dissociatively on both oxides by forming metal-F and O-H bonds. HF coverages ranging from 1.0 0.3 to 17.0 0.3 HF/nm2 are investigated and a mixture of molecularly and dissociatively adsorbed HF molecules is present at higher coverages. Theoretical etch rates of -0.61 0.02 Å /cycle for HfO2 and -0.57 0.02 Å /cycle ZrO2 were calculated using maximum coverages of 7.0 0.3 and 6.5 0.3 M-F bonds/nm2 respectively (M = Hf, Zr).</div>

Ligand Assisted Volatilization and Thermal Stability of [(t-BuN=)2MoCl2]2

2019 ◽  
Author(s):  
Michael Land ◽  
Katherine Roberston ◽  
Sean Barry
Keyword(s):  
Thermal Stability ◽  
Ligand Exchange ◽  
Atomic Layer ◽  
Exchange Reactions ◽  
X Ray Crystallography ◽  
Layer Deposition ◽  
Neutral Ligands ◽  
Solid State Structures ◽  
Tga And Dsc ◽  
Thermal Stability Of

Volatile molybdenum containing compounds have successfully been utilized for the atomic layer deposition of MoN<i><sub>x</sub></i>, MoO<sub>3</sub>, MoS<sub>2</sub>, and MoC<i><sub>x</sub></i>N<i><sub>y</sub></i>. Most of the reported volatile molybdenum containing compounds have been prepared via salt metathesis reactions of <i>bis</i>(<i>tert</i>-butylimido)-dichloromolybdenum(VI), with anionic nitrogen based ligands. Herein we describe the preparation of several adducts of [(<i>t</i>-BuN=)<sub>2</sub>MoCl<sub>2</sub>]<sub>2</sub> (<b>2</b>) <i>via</i> ligand exchange reactions with various neutral ligands, including both mono- and bidentate ethers, amines, and phosphines, as well as an <i>N</i>-heterocyclic carbene (NHC). These compounds have been characterized using NMR spectroscopy, elemental analysis, and the solid-state structures have been determined using single crystal X-ray crystallography. The volatility and thermal stability of all compounds have been assessed using TGA and DSC, showing that the coordinated ligands can improve the volatility, but in many cases the gas phase species reverts to <b>2</b>. This highlights a strategy for using coordinative ligands that are easily thermolyzed during evaporation and delivery yet improve the volatility of a key precursor.

scholarly journals Origin of Enhanced Thermal Atomic Layer Etching of Amorphous HfO2

2021 ◽  
Author(s):  
Rita Mullins ◽  
Jose Julio Gutiérrez Moreno ◽  
Michael Nolan
Keyword(s):  
Metal Oxides ◽  
First Principles ◽  
Etch Rate ◽  
Atomic Layer ◽  
Atomic Level ◽  
Oxide Surface ◽  
Exchange Reactions ◽  
Adsorption Sites ◽  
High K ◽  
Atomic Layer Etching

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 (SL) fluorination and ligand-exchange reactions at elevated temperatures. First-principles based atomic-level simulations using density functional theory (DFT) can give deep insights into the precursor chemistry and the reactions that drive the etch 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 is studied to understand the mechanistic details of the HF pulse. A 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 allows for more binding sites during fluorination whereas crystalline HfO2 has a limited number of adsorption sites.

Mechanism of the HF Pulse in the Thermal Atomic Layer Etch of HfO2 and ZrO2: A First Principles Study

2019 ◽  
Author(s):  
Rita Mullins ◽  
Suresh Natarajan ◽  
Simon D. Elliott ◽  
Michael Nolan
Keyword(s):  
First Principles ◽  
Ligand Exchange ◽  
Elevated Temperatures ◽  
Atomic Layer ◽  
Level Control ◽  
Exchange Reactions ◽  
Nanoscale Device ◽  
High K ◽  
Reaction Models ◽  
High K Materials

<div>HfO2 and ZrO2 are two high-k materials that are important in the down-scaling of semiconductor devices. Atomic level control of material processing is required for fabrication of thin films of these materials at nanoscale device sizes. Thermal Atomic Layer Etch (ALE) of metal oxides, in which up to one monolayer of the material can be removed, can be achieved by sequential self-limiting fluorination and ligand-exchange reactions at elevated temperatures. However, to date a detailed atomistic understanding of the mechanism of thermal ALE of these technologically important oxides is lacking. In this paper, we investigate the hydrogen fluoride pulse in the first step in the thermal ALE process of HfO2 and ZrO2 using first principles simulations. We introduce Natarajan-Elliott analysis, a thermodynamic methodology, to compare reaction models representing the self-limiting (SL) and continuous spontaneous etch (SE) processes taking place during an ALE pulse. Applying this method to the first HF pulse on HfO2 and ZrO2 we found that thermodynamic barriers impeding continuous etch are present at ALE relevant temperatures. We performed explicit HF adsorption calculations on the oxide surfaces to understand the mechanistic details of the HF pulse. A HF molecule adsorbs dissociatively on both oxides by forming metal-F and O-H bonds. HF coverages ranging from 1.0 0.3 to 17.0 0.3 HF/nm2 are investigated and a mixture of molecularly and dissociatively adsorbed HF molecules is present at higher coverages. Theoretical etch rates of -0.61 0.02 Å /cycle for HfO2 and -0.57 0.02 Å /cycle ZrO2 were calculated using maximum coverages of 7.0 0.3 and 6.5 0.3 M-F bonds/nm2 respectively (M = Hf, Zr).</div>

scholarly journals Ligand Assisted Volatilization and Thermal Stability of [(t-BuN=)2MoCl2]2

2019 ◽  
Author(s):  
Michael Land ◽  
Katherine Roberston ◽  
Sean Barry
Keyword(s):  
Thermal Stability ◽  
Ligand Exchange ◽  
Atomic Layer ◽  
Exchange Reactions ◽  
X Ray Crystallography ◽  
Layer Deposition ◽  
Neutral Ligands ◽  
Solid State Structures ◽  
Tga And Dsc ◽  
Thermal Stability Of

Volatile molybdenum containing compounds have successfully been utilized for the atomic layer deposition of MoN<i><sub>x</sub></i>, MoO<sub>3</sub>, MoS<sub>2</sub>, and MoC<i><sub>x</sub></i>N<i><sub>y</sub></i>. Most of the reported volatile molybdenum containing compounds have been prepared via salt metathesis reactions of <i>bis</i>(<i>tert</i>-butylimido)-dichloromolybdenum(VI), with anionic nitrogen based ligands. Herein we describe the preparation of several adducts of [(<i>t</i>-BuN=)<sub>2</sub>MoCl<sub>2</sub>]<sub>2</sub> (<b>2</b>) <i>via</i> ligand exchange reactions with various neutral ligands, including both mono- and bidentate ethers, amines, and phosphines, as well as an <i>N</i>-heterocyclic carbene (NHC). These compounds have been characterized using NMR spectroscopy, elemental analysis, and the solid-state structures have been determined using single crystal X-ray crystallography. The volatility and thermal stability of all compounds have been assessed using TGA and DSC, showing that the coordinated ligands can improve the volatility, but in many cases the gas phase species reverts to <b>2</b>. This highlights a strategy for using coordinative ligands that are easily thermolyzed during evaporation and delivery yet improve the volatility of a key precursor.

Voltammetric Studies of Some Novel Fe(III) Complexes with Quadridentate Ligands. The Axial Ligand-Exchange Reactions in DMF and DMSO

1995 ◽  
Vol 60 (7) ◽  
pp. 1140-1157 ◽  
Author(s):  
Ljiljana S. Jovanovic ◽  
Luka J. Bjelica
Keyword(s):  
Oxidation State ◽  
Chemical Reactions ◽  
Ligand Exchange ◽  
Kinetic Data ◽  
Central Atom ◽  
Axial Ligand ◽  
Exchange Reactions ◽  
Ligand Effect ◽  
Condensation Products ◽  
Voltammetric Studies

The electrochemistry of four novel Fe(III) complexes of the type [Fe(L)Cl], involving quadridentate ligands based on the condensation products of benzoylacetone-S-methylisothiosemicarbazone with salicylaldehyde, 5-chlorosalicylaldehyde, 3,5-dichlorosalicylaldehyde or 5-nitrosalicylaldehyde, was studied in DMF and DMSO at a GC electrode. All complexes undergo a two-step one-electron reductions, usually complicated by chemical reactions. In solutions containing Cl-, the ligand-exchange reactions Cl--DMF and Cl--DMSO take place. Stability of the chloride-containing complexes was discussed in terms of the coordinated ligand effect, oxidation state of the central atom and, in particular, of the donor effect of the solvent. Some relevant kinetic data were calculated.

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