Atomic Layer Deposition Mechanism Research Articles

Understanding Growth Mechanism of Atomic Layer Deposition of Tisiox for Spacer in Double Patterning Process

The aggressive scaling down of patterning technology in semiconductor industry is challenging owing to the limitation of current extreme ultraviolet EUV lithography technique, thus applying self-aligned double patterning (SADP) is essential. In this regard, TiSiOx may be a promising spacer material for SADP, which is beneficial to tolerate high aspect ratio structure triggered by shrinkage in patterning size. However, atomic layer deposition (ALD) of quaternary materials is usually faced to unexpected growth characteristics leading to undesired film qualities, while precise control of thickness and film properties is vital to achieve SADP. This work provide understanding of how growth characteristics of ALD TiSiOx are deviated according to process temperature. At 100 °C, hygroscopic TiSiOx surface which is originated by the presence of Ti-O-Si bond is exposed to H2O by-product leading to enhanced growth rate of TiSiOx compared to ideal case. If the process temperature is increased to 200 °C, opposite behavior is observed since hygroscopic TiSiOx surface characteristic is no more dominant to growth rate of ALD TiSiOx due to dehydroxylation. Theses nonconventional growth characteristics dramatically influence on hydroxyl concentration in TiSiOx films resulting in different spacer qualities such as dry etch rate and elastic modulus. These correlative results suggest that the process conditions should be modulated to suppress hydroxyls incorporation into growing TiSiOx surface during ALD to obtain a high-quality TiSiOx thin films for SADP.

Modeling the Atomic Layer Deposition of Metal Thin Films: Studying the Surface Reaction Mechanism By Density Functional Theory Simulations

Atomic layer deposition (ALD) is widely used in microelectronics and semiconductor industry to deposit thin films as part of device fabrication in nano- or subnano-dimensions. The key advantages of ALD are the conformality and precise thickness control at the atomic scale, which are difficult for physical or traditional chemical vapor deposition methods. The atomic scale understanding of ALD is vital and essential to design and optimize the deposition process, where density functional theory (DFT) calculations play an important role in providing detailed reaction mechanism, theoretical screening of suitable precursors and estimated growth-per-cycle (GPC).In this study, we show our recent works on DFT calculations of the growth mechanism study of Cobalt (Co) thin film by plasma-enhanced ALD1,2. We first addressed the surface reaction mechanism at the metal precursor pulse and plasma half-cycle on NHx-terminated Co surfaces, which corresponds to the steady growth for the PE-ALD. The adsorption and reactions of metal precursors (CoCp2) on NHx terminated metal surfaces were investigated with the inclusion of van der Waals corrections. The plausible reaction pathways include: precursor adsorption, hydrogen transfer, CpH formation and CpH desorption. The direct Cp dissociation mechanism is not considered on these NHx-terminated metal surfaces due to experimentally observed minimal C impurities at the deposited metal thin films, which indicates that most of the Cp ligand is removed completely. The barrier for proton transfer was calculated using climbing image nudged elastic band (CI-NEB) method.The reactions at the initial stages on typical H:Si(100) surface are investigated to gain atomic insight on the effect of different substrates on the elimination of Cp ligands. Our work is important to reveal the mechanism and feasibility of atomic layer deposition of metals using N-plasma.In addition, we present our recent works3, 4 on the thermal ALD of Co using reducing agent Zn(DMP)2 and thermal ALD of Fe4Zn9 thin film with diethyl zinc (DEZ). Our DFT results show that by selecting suitable reducing agent, we can control the deposited thin films to be Zn-free high quality Co thin film or desired intermetallic thin film with high Zn content.These DFT results are important to understand the reaction mechanism for ALD and provides new knowledge in depositing the thin films by adjusting the reducing agents.

Growth behavior and mechanism of atomic layer deposition of Ru for replacing Cu-interconnects

The growth behavior and nucleation mechanism of Ru films on various substrates using Ru(EtCp)2 as the precursor and O2 as the reactant were studied systematically. The results show that the Ru films grow rapidly on TiN substrates with almost no incubation time. Different of the segregation and combustion mechanism reported in the previous literature, we established the adsorption and combustion mechanism of ALD-Ru on TiN substrates. SEM and XPS confirmed that the grown Ru films were polycrystalline (average grain size of 16.53 nm, negligible impurities). The Ru films annealed at 600 °C showed significantly low resistivity of 9.73 μΩ•cm, which is one of the lowest resistivities reported in the literature so far. Suppressing electron scattering at grain boundaries is crucial factor to preparing Ru films with low resistivity. The work uses a simple plasma-free technique to construct high-quality Ru films with extremely low resistivity and low impurities, making them one of the ideal candidates for replacing Cu in future ultrafine-pitch interconnects. Furthermore, the work is significant for understanding the growth behaviors and nucleation mechanisms of Ru films on different substrates.

Atomic layer deposition of magnetic thin films: Basic processes, engineering efforts, and road forward

Atomic layer deposition (ALD) is known as a key enabler of the continuous advances in device engineering for microelectronics. For instance, the state-of-the-art transistor technology depends entirely on ALD-grown high-κ materials. Another application branch where ALD could potentially play a similar important role in future is the magnetic thin film devices. Spin-based devices based on high-quality magnetic thin films are anticipated to provide high-efficiency operations with low power consumption. The strict quality demands the magnetic thin films must fulfill in the next-generation applications form the strong bases for the efforts to implement ALD in this application area. In this first comprehensive review on the topic, our aim is to provide an insightful account of the ALD processes so far developed for magnetic materials and to highlight the application-relevant magnetic properties of the thus fabricated thin films. Moreover, we discuss the various innovative engineering efforts made toward different multi-layered and nanostructured composite materials and complex architectures uniquely enabled by the sophisticated self-terminated film-growth mechanism of ALD. The review is finished with a brief outlook toward the future prospects and challenges in the field.

Surface reaction mechanism of atomic layer deposition of niobium oxide: In situ characterization and first-principle study

We report the surface reaction mechanism of the atomic layer deposition (ALD) of niobium oxide films by combining experimental and theoretical studies. Tert-butylimido tris(dimethylamido)niobium [tBuN=Nb(NMe2)3] and ozone (O3) were studied as the precursor and co-reactant. The in situ quartz crystal microbalance (QCM) analysis predicted that two HNMe2 molecules or one H2NtBu molecule were released at 200 °C per one molecule tBuN=Nb(NMe2)3. Since the QCM alone could not distinguish two possible reaction pathways, we compared two pathways by density functional theory (DFT) calculations. We simulated the chemisorption of the precursor molecule on the –OH terminated T-Nb2O5 substrate. The release of two –NMe2 ligands was favorable due to low activation energies of 0.71 and 0.63 eV for the first and second releases. On the other hand, the release of =NtBu was not favorable due to the high activation energy of 1.50 eV. Therefore, the amido and imido ligands were actor and spectator ligands during the first half-reaction of the ALD of niobium oxide films. The combination of QCM and DFT could successfully reveal the surface reaction mechanism of the ALD process using a heteroleptic precursor.

Nucleation and growth mechanism for atomic layer deposition of Al2O3 on two-dimensional WS2 monolayer

Nanoelectronics holds significant promise for two-dimensional (2D) semiconducting transition metal dichalcogenide (TMD) applications. On a polycrystalline WS2 monolayer created by metal-organic chemical vapor deposition (MOCVD) at 950 °C, we studied the nucleation, growth, and development of Al2O3 atomic layer deposition (ALD) on a SiO2/Si substrate. In this investigation, we used various complementary characterization methods, such as Raman spectroscopy, elastic recoil detection, atomic force microscopy, and time-of-flight secondary ion mass spectrometry, to understand thoroughly the intrinsic reactivity of WS2. Strong peak intensity changes at the interfaces in the Raman line scans of the SiO2/Si patterns suggest extremely crystalline WS2. After multiple ALD cycles, triangular WS2 crystals were decorated to provide a two-dimensional growth mode with a great selectivity for grain boundaries and step edges. The results of this work can be used for further exploration of the TMD monolayer structure and properties, which is essential for tailoring 2D materials for a specific application in devices.

(Digital Presentation) Simultaneous Transforming Residual Lithium Compounds and Stabilizing Surface Lattice Oxygen for Ni-Rich Cathode Via Atomic Layer Deposition and Post-Annealing

Unstable surface species such as residual lithium compounds and surface lattice oxygen at charge state are detrimental factors for the battery performance of Ni-rich cathode (LiNixCoyMn1−x−yO2, x ≥ 0.6, NCM), which induce serious side reactions and lead to rapid capacity loss during cycling. With the advantages of sufficient contacts between gas and solid, gas reactants are introduced to reducing residual lithium compounds via gas-solid reactions or building protective coatings to isolate surface lattice oxygen from the electrolyte via gas-phase deposition, which effectively enhances the cycling stability of NCM. Atomic layer deposition (ALD), as a special coating technology, possesses both the nature of the gas-solid reaction and gas-phase deposition. It is significant to investigate the mechanism of ALD in enhancing the cycling stability of NCM.Here, we report a method to improving the rate capacity and cycling stability of single-crystal NCM via Al2O3 and B2O3 ALD by constructing a highly Li-ions conductive and electrochemical stable surface. The ultrathin coatings are uniformly coated on the surface of NCM. Moreover, surface composition characterizations show the reductions of residual lithium compounds and formations of lithium-containing coatings after the ALD process. By adding a post-annealing process, Al3+ cations and BO3- polyanions doping form on the surface of NCM, which robustly enhanced the stability of surface lattice oxygen of NCM via strong Al-O bond and B-O bond. Moreover, as acidic oxides, B2O3 shows better performance than Al2O3 in reducing residual lithium compounds during the ALD process. Different from Al3+ cations doping occupying the transition metal ions position, BO3- polyanions doping occupies the oxygen ions position, which does not deteriorate the capacity of NCM. Transformation of residual lithium compounds and stabilizing surface lattice oxygen on NCM greatly decrease the formation of LiF and degradation of surface structure, which is the key to the improvement of rate capacity and cycling stability.

(Invited) ALD of FeSe2, CoSe2, and NiSe2

The iron-group transition-metal diselenides (MSe2, M = Fe, Co, Ni) have recently gained tremendous interest in many areas. The MSe2 compounds normally form similar pyrite or marcasite crystal structures, and, with a progressive increase in the metal 3d electrons, FeSe2, CoSe2, and NiSe2 exhibit diverse and fascinating optical, magnetic, and electrical properties. In this talk, I will present our latest progress on the atomic layer deposition (ALD) of FeSe2, CoSe2, and NiSe2. These ALD processes employ the corresponding metal amidinates as the metal precursors and diethyldiselenide (DEDSe) as the selenium precursor, together with Ar/H2 plasma for DEDSe activation. All of the ALD processes are able to grow pure, smooth, and crystalline MSe2 (M = Fe, Co, Ni) films, and the MSe2 films can also be uniformly deposited into 10:1 high-aspect-ratio microtrenches with excellent conformality, which thereby shows the great promise for conformal coating on 3D complex topologies in general. In situ ALD mechanism investigation further reveals that the efficient dissociation of DEDSe by plasma is key to the success of these ALD processes.

Surface Reaction Mechanism of Atomic Layer Deposition of Niobium Oxide: In Situ Characterization and First-Principle Study

Surface Reaction Mechanism of Atomic Layer Deposition of Niobium Oxide: In Situ Characterization and First-Principle Study

Improved Monolayer MoS Performance With Two-Step Atomic Layer Deposited High- Dielectrics

Gate dielectric engineering is crucial to enable two-dimensional (2D) transition metal dichalcogenides (TMDs) for logic transistor applications. In this work, we demonstrate a uniform and pinhole-free bilayer high-K fabricated on monolayer (1L) molybdenum disulfide (MoS2) through thermal atomic layer deposition (ALD) without surface pretreatment. A thin low-temperature (75∘C) AlOx film deposited directly on 1L-MoS2 mitigates 2D channel damage and serves as a nucleation and protection layer for high-temperature (250∘aC) HfOx high-K layer. The 1L-MoS2 back-gate (BG) devices with low-temperature ALD capping show minor mobility degradation, less threshold voltage shift, smooth surface topography, and lower device variability compared to those with high-temperature ALD capping. These electrical differences are closely related to the coverage of the AlOx film at the initial ALD stage and the resultant quality of the AlOx -MoS2 interface after HfOx deposition. The underlying mechanism of ALD on the TMDs is proposed in terms of physical analysis and electrical findings. This work provides a practical and scalable ALD approach in gate dielectrics toward high performance 2D electronics.

Comparison of the Growth and Thermal Properties of Nonwoven Polymers after Atomic Layer Deposition and Vapor Phase Infiltration

The growth mechanism of Atomic Layer Deposition (ALD) on polymeric surfaces differs from growth on inorganic solid substrates, such as silicon wafer or glass. In this paper, we report the growth experiments of Al2O3 and ZnO on nonwoven poly-L-lactic acid (PLLA), polyethersulphone (PES) and cellulose acetate (CA) fibres. Material growth in both ALD and infiltration mode was studied. The structures were examined with a scanning electron microscope (SEM), scanning transmission electron microscope (STEM), attenuated total reflectance-fourier-transform infrared spectroscopy (ATR-FTIR) and 27Al nuclear magnetic resonance (NMR). Furthermore, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis were used to explore the effect of ALD deposition on the thermal properties of the CA polymer. According to the SEM, STEM and ATR-FTIR analysis, the growth of Al2O3 was more uniform than ZnO on each of the polymers studied. In addition, according to ATR-FTIR spectroscopy, the infiltration resulted in interactions between the polymers and the ALD precursors. Thermal analysis (TGA/DSC) revealed a slower depolymerization process and better thermal resistance upon heating both in ALD-coated and infiltrated fibres, more pronounced on the latter type of structures, as seen from smaller endothermic peaks on TA.

Reaction Mechanisms of Non-hydrolytic Atomic Layer Deposition of Al2O3 with a Series of Alcohol Oxidants

Atomic layer deposition (ALD) of Al2O3 using trimethylaluminum (TMA) and H2O is the most widely and deeply studied ALD process owing to the superior properties of the deposited Al2O3 thin films and usability of TMA and H2O. However, H2O can cause undesirable substrate oxidation during ALD. While previous studies have shown that alcohol oxidants can be used to deposit Al2O3 thin films with less substrate oxidation, the reaction mechanism of ALD Al2O3 with alcohol oxidants has not been elucidated yet. In this study, the reaction mechanism of ALD of Al2O3 thin films using various alcohol oxidants was systematically investigated by computational and experimental methods. Various possible reaction pathways are considered for the oxidation of Al–CH3 with methanol (MeOH), ethanol (EtOH), and propanol (n-PrOH). It is found that the feasible reaction mechanism for removal of the surface-adsorbed alkoxy group is autocatalytic liberation of alkene through β-hydrogen transfer. ALD processes were developed using the alcohol oxidants. Our process using EtOH showed a growth rate of 0.96 Å/cycle and a moderate level of carbon impurities (2.6%). In addition, we investigated the properties of ALD-deposited Al2O3 thin films with alcohol oxidants, which indicated superior electrical properties and decreased formation of interfacial oxide on the Si substrate.

The Growth Mechanisms of Atomic Layer Deposition: An Overview

In this review, the discussion emphasized on the growth mechanisms of atomic layer deposition which consists of a theoretical model and experimentally growth as well as the measurement testing as evidences. The deposition process description with some testing evidences can be used to facilitate in the effort to understand the basic concept of ALD growth mechanisms. Some metal oxides like Al2O3, HfO2, and TiO2 with these employed precursors are typically used for the detailed illustration during the reaction steps. Although the surface chemistry of ALD process has been well understood, systematic description which combine a theoretical and experimentally growth mechanism is still missing. This paper aims to provide a better understanding of ALD growth mechanisms and surface chemistry which eventually able to contribute on the thin film growth processing.

(Invited) Elucidating the Mechanisms for Atomic Layer Growth through in Situ Studies

Atomic Layer Deposition (ALD) provides exquisite control over film thickness and composition and yields excellent conformality over large areas and within nanostructures. These desirable attributes derive from self-limiting surface chemistry, and can disappear if the self-limitation is removed. Understanding the surface chemical reactions, i.e. the ALD mechanism, can provide insight into the limits of self-limitation allowing better control, successful scale up, and the invention of new processes. In situ measurements are very effective for elucidating ALD growth mechanisms. In this presentation, I will describe investigations into the growth mechanisms of ALD nanocomposite films comprised of conducting (e.g. W, Mo and Re) and insulating (e.g. Al2O3, ZrO2 and TiO2) components using in situ measurements. These ALD nanocomposites have applications in particle detection, energy storage, and solar power. We have performed extensive in situ studies using quartz crystal microbalance (QCM), quadrupole mass spectrometry (QMS), Fourier transform infrared (FTIR) absorption spectroscopy, and current-voltage measurements. These measurements reveal unusual ALD chemistry occurring upon transitioning between the ALD processes for the two components. This results in unique reaction products that affect the properties of the films in beneficial ways. The knowledge gained from our in situ studies of the ALD nanocomposite films has helped us to overcome problems encountered when we scaled up the ALD processes to large area substrates. Beyond fundamental understanding, in situ measurements are extremely effective in ALD process development and process monitoring. I will end my talk by describing our recent work combining in situ measurements and machine learning to accelerate ALD process development.

Unveiled Understanding on Thermodynamic Mechanisms of Atomic Layer Deposition Based on Trimethylaluminum and Water Precursors

Despite the importance of the atomic layer deposition (ALD) technique for developing thin films of various inorganic materials with the precisely controlled thickness, the detailed mechanistic pathway and thermodynamics of the ALD processes are not fully understood. In this study, the first-principles density functional theory calculations for ALD of Al2O3 are employed to explore the reaction thermodynamics in the chemical adsorption of trimethylaluminum (TMA) and water during the TMA- and H2O-dosed half-cycles of ALD. Three primary conclusions are highlighted from this investigation. (i) Despite the intrinsic nature of the TMA molecule with higher thermodynamic stability in a dimeric form than in a monomeric form, the TMA molecules would prefer to be chemisorbed on Al2O3(0001) surfaces in a monomeric form during the TMA-dosed half-cycle, exhibiting the highest stability for the monomeric TMA adsorbates in bidentate configurations under the assumption of the presence of abundant hydroxyl adsorption sites. (ii) The energy profile for the chemisorption of water molecules during the H2O-dosed half-cycle would strongly rely on the configuration of the TMA adsorbates formed in the previous TMA-dosed half-cycle, especially at the early stage of the H2O-dosed half-cycle. (iii) The thermodynamic feasibility of the water molecules chemisorbed after the early stage of the H2O-dosed half-cycle would not be significantly varied in real ALD processes.

Atomic Layer Deposition of ZnO on Mesoporous Silica: Insights into Growth Behavior of ZnO via In-Situ Thermogravimetric Analysis.

ZnO is a remarkable material with many applications in electronics and catalysis. Atomic layer deposition (ALD) of ZnO on flat substrates is an industrially applied and well-known process. Various studies describe the growth of ZnO layers on flat substrates. However, the growth characteristics and reaction mechanisms of atomic layer deposition of ZnO on mesoporous powders have not been well studied. This study investigates the ZnO ALD process based on diethylzinc (DEZn) and water with silica powder as substrate. In-situ thermogravimetric analysis gives direct access to the growth rates and reaction mechanisms of this process. Ex-situ analytics, e.g., N2 sorption analysis, XRD, XRF, HRTEM, and STEM-EDX mapping, confirm deposition of homogenous and thin films of ZnO on SiO2. In summary, this study offers new insights into the fundamentals of an ALD process on high surface area powders.

Recent advances in mechanism investigation of atomic layer deposition by <italic>in situ</italic> photoelectron spectroscopy

Atomic layer deposition (ALD) is an emerging vapor-phase thin-film deposition technique, and it has been widely used in microelectronics, energy, optics, and catalysis. Studying and understanding the physicochemical mechanisms involved in the ALD processes are essential to grow high-quality films and for their applications. As a surface-sensitive techinique, photoelectron spectroscopy (PES) is capable of in situ monitoring the surface chemistries during ALD, which provides the essential information for the mechanism investigation and process development of ALD. This review is organized to first introduce the working principles and instrumentation of coupling ALD with in situ PES for studying the ALD mechanisms, and then describes in detail the recent research advances in using the in situ PES technique to study the surface chemistry reactions during the film growth, the substrate effects during the intital growth, the modes of film growth, the surface thermolysis of the precursors and the effects thereof, and the band structures at the interfaces. Finally, the perspectives on the future directions of the ALD mechanism studies by PES are onlined.

Polyphenol‐Sensitized Atomic Layer Deposition for Membrane Interface Hydrophilization

AbstractImprovements in energy–water systems will necessitate fabrication of high‐performance separation membranes. To this end, interface engineering is a powerful tool for tailoring properties, and atomic layer deposition (ALD) has recently emerged as a promising and versatile approach. However, most non‐polar polymeric membranes are not amenable to ALD processing due to the absence of nucleation sites. Here, a sensitization strategy for ALD‐coating is presented, illustrated by membrane interface hydrophilization. Facile dip‐coating with polyphenols effectively sensitizes hydrophobic polymer membranes to TiO2 ALD coating. Tannic acid‐sensitized ALD‐coated membranes exhibit outstanding underwater crude oil repulsion and rigorous mechanical stability through bending and rinsing tests. As a result, these membranes demonstrate outstanding crude oil‐in‐water separation and reusability compared to untreated membranes or those treated with ALD without polyphenol pretreatment. A possible polyphenol‐sensitized ALD mechanism is proposed involving initial island nucleation followed by film intergrowth. This polyphenol sensitization strategy enriches the functionalization toolbox in material science, interface engineering, and environmental science.

Application of time-of-flight secondary ion mass spectrometry to the detection of surface intermediates during the first cycle of atomic layer deposition (ALD) of platinum on silica surfaces

Abstract Atomic layer deposition (ALD) has become the method of choice for many applications requiring the controlled growth of thin films on solid surfaces. However, the use of metalorganic precursors typical in these depositions adds significant complexity to the chemistry involved. Unfortunately, it is difficult to obtain direct information about the surface species that participate in the reaction mechanisms of ALD. Here we illustrate the value of using time-of-flight secondary ion mass spectrometry (ToF-SIMS) for this purpose. A particular example is provided, a study of the first cycle of deposition of platinum using trimethyl(methylcyclopentadienyl)platinum (IV), or MeCpPt(CH3)3, on silicon oxide surfaces. In previous investigations of this process, we have determined that the low reactivity of the MeCpPt(CH3)3 precursor, which hinders fast deposition, can be partially overcome by gas-phase electron-impact activation. What has not been clear is what chemical species form on the solid surface as a result of such activation. Here we show that the MeCp ligand is quite stable and that it remains intact and coordinated to the Pt atoms upon adsorption on the surface. It was also established that some of the methyl groups may remain bound to the Pt center: the main species detected on the silicon oxide surfaces were MeCpPt and MeCpPt(CH3). On the other hand, it appears that no Pt intermediates without MeCp ligands are formed during this initial adsorption. Finally, O2 treatment of these surfaces at elevated temperature to complete the first ALD cycle leads to the complete removal of all the organic ligands: no evidence for MeCp or methyl groups is seen in the ToF-SIMS traces from the final samples.

Low-Temperature Wafer-Scale Deposition of Continuous 2D SnS2 Films.

Semiconducting 2D materials, such as SnS2 , hold immense potential for many applications ranging from electronics to catalysis. However, deposition of few-layer SnS2 films has remained a great challenge. Herein, continuous wafer-scale 2D SnS2 films with accurately controlled thickness (2 to 10 monolayers) are realized by combining a new atomic layer deposition process with low-temperature (250 °C) postdeposition annealing. Uniform coating of large-area and 3D substrates is demonstrated owing to the unique self-limiting growth mechanism of atomic layer deposition. Detailed characterization confirms the 1T-type crystal structure and composition, smoothness, and continuity of the SnS2 films. A two-stage deposition process is also introduced to improve the texture of the films. Successful deposition of continuous, high-quality SnS2 films at low temperatures constitutes a crucial step toward various applications of 2D semiconductors.