Mechanism for the Atomic Layer Deposition of Copper Using Diethylzinc as the Reducing Agent: A Density Functional Theory Study Using Gas-Phase Molecules as a Model

Atomic Layer Deposition of Intermetallic Fe4Zn9 Thin Films from Diethyl Zinc

We present a new type of atomic layer deposition (ALD) process for intermetallic thin films, where diethyl zinc (DEZ) serves as a coreactant. In our proof-of-concept study, FeCl₃ is used as the second precursor. The FeCl₃ + DEZ process yields in situ crystalline Fe₄Zn₉ thin films, where the elemental purity and Fe/Zn ratio are confirmed by time-of-flight elastic recoil detection analysis (TOF-ERDA), Rutherford backscattering spectrometry (RBS), atomic absorption spectroscopy (AAS), and energy-dispersive X-ray spectroscopy (EDX) analyses. The film thickness is precisely controlled by the number of precursor supply cycles, as expected for an ALD process. The reaction mechanism is addressed by computational density functional theory (DFT) modeling. We moreover carry out preliminary tests with CuCl₂ and Ni(thd)₂ in combination with DEZ to confirm that these processes yield Cu-Zn and Ni-Zn thin films with DEZ as well. Thus, we envision an opening of a new ALD approach based on DEZ for intermetallic/metal alloy thin films.

Recent Advances in Theoretical Development of Thermal Atomic Layer Deposition: A Review

Atomic layer deposition (ALD) is a vapor-phase deposition technique that has attracted increasing attention from both experimentalists and theoreticians in the last few decades. ALD is well-known to produce conformal, uniform, and pinhole-free thin films across the surface of substrates. Due to these advantages, ALD has found many engineering and biomedical applications. However, drawbacks of ALD should be considered. For example, the reaction mechanisms cannot be thoroughly understood through experiments. Moreover, ALD conditions such as materials, pulse and purge durations, and temperature should be optimized for every experiment. It is practically impossible to perform many experiments to find materials and deposition conditions that achieve a thin film with desired applications. Additionally, only existing materials can be tested experimentally, which are often expensive and hazardous, and their use should be minimized. To overcome ALD limitations, theoretical methods are beneficial and essential complements to experimental data. Recently, theoretical approaches have been reported to model, predict, and optimize different ALD aspects, such as materials, mechanisms, and deposition characteristics. Those methods can be validated using a different theoretical approach or a few knowledge-based experiments. This review focuses on recent computational advances in thermal ALD and discusses how theoretical methods can make experiments more efficient.

Understanding chemical and physical mechanisms in atomic layer deposition

Atomic layer deposition (ALD) is a powerful tool for achieving atomic level control in the deposition of thin films. However, several physical and chemical phenomena can occur which cause deviation from "ideal" film growth during ALD. Understanding the underlying mechanisms that cause these deviations is important to achieving even better control over the growth of the deposited material. Herein, we review several precursor chemisorption mechanisms and the effect of chemisorption on ALD growth. We then follow with a discussion on diffusion and its impact on film growth during ALD. Together, these two fundamental processes of chemisorption and diffusion underlie the majority of mechanisms which contribute to material growth during a given ALD process, and the recognition of their role allows for more rational design of ALD parameters.

Classification of processes for the atomic layer deposition of metals based on mechanistic information from density functional theory calculations

Reaction cycles for the atomic layer deposition (ALD) of metals are presented, based on the incomplete data that exist about their chemical mechanisms, particularly from density functional theory (DFT) calculations. ALD requires self-limiting adsorption of each precursor, which results from exhaustion of adsorbates from previous ALD pulses and possibly from inactivation of the substrate through adsorption itself. Where the latter reaction does not take place, an "abbreviated cycle" still gives self-limiting ALD, but at a much reduced rate of deposition. Here, for example, ALD growth rates are estimated for abbreviated cycles in H₂-based ALD of metals. A wide variety of other processes for the ALD of metals are also outlined and then classified according to which a reagent supplies electrons for reduction of the metal. Detailed results on computing the mechanism of copper ALD by transmetallation are summarized and shown to be consistent with experimental growth rates. Potential routes to the ALD of other transition metals by using complexes of non-innocent diazadienyl ligands as metal sources are also evaluated using DFT.

Modeling Mechanism and Growth Reactions for New Nanofabrication Processes by Atomic Layer Deposition

Recent progress in the simulation of the chemistry of atomic layer deposition (ALD) is presented for technologically important materials such as alumina, silica, and copper metal. Self-limiting chemisorption of precursors onto substrates is studied using density functional theory so as to determine reaction pathways and aid process development. The main challenges for the future of ALD modeling are outlined.

Quantum chemical and solution phase evaluation of metallocenes as reducing agents for the prospective atomic layer deposition of copper

We propose and evaluate the use of metallocene compounds as reducing agents for the chemical vapour deposition (and specifically atomic layer deposition, ALD) of the transition metal Cu from metalorganic precursors.

Surface chemistry of copper metal and copper oxide atomic layer deposition from copper(ii) acetylacetonate: a combined first-principles and reactive molecular dynamics study

Atomistic mechanisms for the atomic layer deposition using the Cu(acac)₂ (acac = acetylacetonate) precursor are studied using first-principles calculations and reactive molecular dynamics simulations.

Copper reduction and atomic layer deposition by oxidative decomposition of formate by hydrazine

We have used Density Functional Theory (DFT) to study the mechanism of three step atomic layer deposition (ALD) of copper via formate and hydrazine.

CVD of pure copper films from novel iso-ureate complexes

We report the synthesis and characterisation of a new family of copper(i) metal precursors based around alkoxy-N,N'-di-alkyl-ureate ligands, and their subsequent application in the production of pure copper thin films. The molecular structure of the complexes bis-copper(i)(methoxy-N,N'-di-isopropylureate) (1) and bis-copper(i)(methoxy-N,N'-di-cyclohexylureate)(5) are described, as determined by single crystal X-ray diffraction analysis. Thermogravimetric analysis of the complexes highlighted complex 1 as a possible copper CVD precursor. Low pressure chemical vapour deposition (LP-CVD) was employed using precursor 1, to synthesise thin films of metallic copper on ruthenium substrates under an atmosphere of hydrogen (H2). Analysis of the thin films deposited at substrate temperatures of 225 °C, 250 °C and 300 °C, respectively, by SEM and AFM reveal the films to be continuous and pin hole free, and show the presence of temperature dependent growth features on the surface of the thin films. Energy dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (PXRD) and X-ray photoelectron spectroscopy (XPS) all show the films to be high purity metallic copper.