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All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Protein-activated atomic layer deposition for robust crude-oil-repellent hierarchical nano-armored membranes

Atomic layer deposition (ALD) offers unique capabilities to fabricate atomically engineered porous materials with precise pore tuning and multi-functionalization for diverse applications like advanced membrane separations towards sustainable energy-water systems. However, current ALD technique is inhibited on most non-polar polymeric membranes due to lack of accessible nucleation sites. Here, in this study, we report a facile method to efficiently promote ALD coating on hydrophobic surface of polymeric membranes via novel protein activation/sensitization. As a proof of concept, TiO 2 ALD-coated membranes activated by bovine serum albumin exhibit remarkable superhydrophilicity, ultralow underwater crude oil adhesion, and robust tolerance to rigorous environments including acid, alkali, saline, and ethanol. Most importantly, excellent cyclable crude oil-in-water emulsion separation performance can be achieved. The mechanism for activation/sensitization is rooted in reactivity for a particular set of amino acids. Furthermore, the universality of protein-sensitized ALD is demonstrated using common egg white, promising numerous potential usages in biomedical engineering, environmental remediation, lowcarbon manufacturing, catalysis, and beyond.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Mechanistically Informed Strategies for Site-Selective Atomic Layer Deposition

While atomic layer deposition (ALD) processes from across the periodic table have been designed to deposit conformal thin films, an atomistic view of disparate substrate sites reveals the possibility of even greater synthetic control and precision. An understanding of the mechanism by which a particular ALD precursor reacts (or does not react) at myriad surface sites remains in its infancy. Here, in this Perspective, we summarize site-specific chemical reaction strategies that utilize ALD precursors and tailored surface chemistry to discriminate among potential deposition sites as well as describe techniques and tools that can be used to investigate site-selective ALD (SS-ALD). The Perspective is focused on the science of site-selective vapor-phase surface reactions but inevitably reveals the potential utility of such surface synthetic precision.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Mechanistic Study of Nucleation Enhancement in Atomic Layer Deposition by Pretreatment with Small Organometallic Molecules

Thermal atomic layer deposition (ALD) of metals on metal oxide surfaces typically suffers from nucleation delays that result in poor-quality films. The poor nucleation may be caused by a lack of suitable chemisorption sites on the oxide surface, which are needed for metal nucleation to occur. In this work, we demonstrate that prefunctionalizing the surface with a single monolayer of small organometallic molecules from the vapor phase can lead to a significant increase in surface coverage of the metal deposited by ALD. This process is demonstrated for Pt ALD from (methylcyclopentadienyl)trimethylplatinum (MeCpPtMe 3 ) and O 2 , with nucleation enhanced almost 3-fold at 100 ALD cycles after the pretreatment. We hypothesize that the high coverage of the organometallic molecule provides an alternative chemisorption mechanism for the platinum precursor and thus leads to an increase in its uptake. The proposed chemisorption mechanism is robust across several organometallic molecule pretreatments and could potentially be exploited for other organometallic-based metal ALD processes. This chemisorption mechanism was probed using in situ quadrupole mass spectrometry (QMS). The growth of the platinum deposits was investigated in depth through scanning electron microscopy (SEM) and grazing incidence small-angle X-ray scattering (GISAXS). These studies show that the pretreatment also results in the improved wettability of Pt nanoparticles (NPs). The improved wettability is likely to affect the Pt diffusion properties, further contributing to the enhancement observed on the treated substrates. In addition, GISAXS and SEM studies indicate the growth of larger, denser, and more highly ordered Pt NPs at early cycle numbers, which subsequently coalesce into continuous and pinhole-free films. Surface pretreatment by organometallic molecules therefore introduces a potential route to achieve improved nucleation and growth of ultrathin films.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Nucleation Effects in the Atomic Layer Deposition of Nickel–Aluminum Oxide Thin Films

Atomic layer deposition (ALD) has become an important technique to synthesize a wide variety of materials on the subnanometer length scale. Expanding the library of ALD for ternary materials is vital for applications in which ternary materials allow for tuning of physical, optical, and electronic properties. In this work reported herein, we demonstrate the first report of nickel–aluminum oxide (Ni–Al–O) films deposited by ALD using nickeloceneozone and trimethylaluminum-water as reactants. While deposition of a wide range of compositions is achieved, the observed growth per cycle (GPC) did not follow the simple combination of GPCs measured for the binary ALD processes. Nucleation studies performed to better understand this behavior reveal that the deposition of aluminum oxide is greatly enhanced on a NiO surface prepared by nickelocene and ozone. A model is developed that considers nucleation effects to predict composition and thickness as a function of supercycle recipe. Characterization of the deposited films shows that Al-doping of NiO results in contraction of the NiO lattice, decreased crystallinity, and reduced density, and that films become completely amorphous at compositions with less than 50% Ni. In addition, Al-doped NiO films deposited by ALD are investigated as a hole-selective transport layer in lead-based perovskite solar cells. An Al doping of ~4% improves power conversion efficiency of the perovskite-based devices over that of NiO primarily through increases in fill factor.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Surface Dynamics of Selective Hydration of Rutile TiO 2 : A Kinetic Monte Carlo Approach

The utility of atomic layer deposition (ALD) continues to expand beyond conformal thin-film fabrication to include area- or site-selective ALD. We previously identified a strategy for site-selective ALD (SS-ALD) via the evaluation of thermodynamically preferred hydration of rutile TiO 2 surfaces, as deduced from electronic structure calculations. Here, we report a novel kinetic Monte Carlo (KMC) model that allows for the investigation of surface dynamics and kinetics that improves our understanding of and intuition for the selective hydration strategy. Here we demonstrate the validity of the strategy with respect to step-edge defects for the lowest energy (110) facet as well as report results for the other common facets which agree with experimental STM observations. The results here indicate that the selective hydration strategy is feasible both thermodynamically (evaluated in our previous publication) and kinetically (from the KMC model). Because diffusion has a slower rate than others, we find that any proximity effects between terrace and defect sites are unlikely to affect the selective hydration strategy for rutile TiO 2 . The KMC model further provides relevant timescales for achieving selectivity experimentally and establishes the kinetic viability of the selective hydration approach to SS-ALD.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Roll-To-Roll Atomic Layer Deposition of Titania Nanocoating on Thermally Stabilizing Lithium Nickel Cobalt Manganese Oxide Cathodes for Lithium Ion Batteries

Conformal coating of ceramic layers (nm-thick) on Ni-rich layered cathode materials is an effective strategy for improving high-temperature longevity of Li-ion batteries (LIBs). In this work, we develop a roll-to-roll atomic layer deposition (R2R ALD) apparatus for growing uniform nanolayers of TiO 2 . We explore the effect of ALD parameters (temperature: 120–180 °C and line speed: 2–40 mm s –1 ) on the TiO 2 surface coating and subsequently investigate the electrochemical performance of the as-prepared cathodes. The capacity retention of TiO 2 -coated porous electrodes is substantially improved compared to that of the pristine cathode material for high-temperature cycling. Electrochemical impedance spectroscopy confirms that the ALD-TiO 2 coating suppresses the undesired side reactions initiated at the electrode/electrolyte interface, reduces charge transfer resistance, and ultimately facilitates the Li + transport through the composite cathode nanostructure. The robust design of the ALD-TiO 2 cathode material enables high-temperature operation (>55 °C) with enhanced specific capacity, superior rate capability, excellent cyclability, and ultra-high coulombic efficiency within a wide potential window (3.0–4.35 V). Furthermore, the R2R ALD technique developed in this work paves the way for large-scale fabrication of ceramic-coated cathode sheets with a production rate reaching 2.4 m min –1 for a continuous coating operation.

25 ENERGY STORAGE↗
DOE OSTI2021

Al2O3 Atomic Layer Deposition on Nanostructured γ-Mg(BH4)2 for H2 Storage

In the context of the growing hydrogen (H 2 ) economy, the demand for H 2 storage materials is high, and metal borohydrides are of particular interest. Magnesium borohydride, Mg(BH 4 ) 2 , has one of the highest hydrogen capacities of all known metal hydrides (14.9 wt % H) but suffers from high operating temperatures, slow kinetics for (de)hydrogenation, and the loss of capacity upon cycling. Strategies to address these challenges include nanoencapsulation and the use of chemical additives. This work is the first to utilize these two strategies simultaneously by using atomic layer deposition (ALD). For this new approach to modify borohydrides, we chose the well-studied Al 2 O 3 ALD process using trimethylaluminum and water. Although there has been limited use of aluminum-based additives for Mg(BH 4 ) 2 , we demonstrate that the low-temperature H 2 capacity was doubled, desorption kinetics were increased by a factor of 3, and 100 cycles of Al 2 O 3 suppressed the release of diborane compared to the uncoated Mg(BH4)2. We identified that the use of trimethylaluminum and water in the ALD process affected the decomposition pathway and that the Al 2 O 3 film growth is dominated by infiltration due to the high porosity of the ..gamma..-phase Mg(BH 4 ) 2 . From these results, the potential of ALD as a method to functionalize solid-state H 2 storage materials is inferred, and recommendations for future ALD processes are presented.

08 HYDROGEN↗
DOE OSTI2022

Removal of Surface Carbonate from Lithium-Ion Battery Cathode Materials via Vapor-Phase Fluorination

Herein, ultrathin metal-fluoride barrier coatings on the surface of lithium-ion battery (LIB) cathodes can improve cycling stability and prevent corrosion by acidic byproducts in the electrolyte. Atomic layer deposition (ALD) is an effective method to deposit ultrathin metal fluoride coatings on LIB cathodes. Although numerous studies have demonstrated the benefit of ALD metal fluoride coatings to LIB performance, comparatively few works have examined the effect of individual ALD precursors on the cathode surface. This paper uses X-ray photoelectron spectroscopy (XPS) measurements to elucidate the surface chemical changes on LIB cathode material surfaces upon exposure to the ALD metal fluoride precursor, hydrogen fluorine pyridine (HFPy). We found a decrease in surface carbonate and an increase in surface fluoride after HFPy exposure suggesting the conversion of lithium carbonate (Li 2 CO 3 ) to lithium fluoride (LiF). This conversion is desirable given that Li 2 CO 3 degrades LIB performance, whereas LiF provides an excellent physio-chemical barrier against chemical attack during cycling. Scanning transmission electron microscopy, X-ray energy dispersive spectroscopy, and XPS measurements following HFPy exposure to Li 2 CO 3 powder revealed the formation of a conformal LiF shell around the Li 2 CO 3 particles. Finally, we confirmed the complete conversion of similar to 7 nm ALD Li 2 CO 3 films on silicon from HFPy exposure using XPS and spectroscopic ellipsometry. The elimination of problematic Li 2 CO 3 from LIB cathode surfaces and conversion into a protective LiF coating via a single precursor vapor treatment may provide a cost-effective method for enhancing LIB performance.

25 ENERGY STORAGE↗
DOE OSTI2026

Small Molecule Inhibitor-Modulated Al 2 O 3 Atomic Layer Deposition on Monolayer MoS 2 for Controlled Nucleation

The integration of ultrathin dielectrics on two-dimensional (2D) semiconductors is essential for advancing beyond-Si electronics. However, the intrinsic inertness of van der Waals 2D basal planes remains a primary bottleneck to achieving uniform dielectric nucleation and growth. Here, in this study, we introduce a small molecule inhibitor (SMI)-modulated thermal atomic layer deposition (ALD) strategy, exemplified by aluminum oxide (Al 2 O 3 ) ALD on monolayer molybdenum disulfide (1L MoS 2 ) with acetic acid (HAc) SMI. The ABC-type sequence comprises HAc inhibitor (A), trimethylaluminum (TMA) precursor (B), and deionized H 2 O coreactant (C). In situ quartz crystal microbalance (QCM) studies reveal robust HAc adsorption on Al 2 O 3 and suppression of subsequent oxide growth on HAc-passivated surfaces. When applied to 1L MoS 2 , this inhibitory pathway enables HAc to selectively passivate nascent Al 2 O 3 nuclei formed on the MoS 2 surface, limiting their three-dimensional (3D) island coarsening and redirecting precursor adsorption toward the uncovered basal plane. Consequently, nearly continuous ultrathin (∼1.5 nm) Al 2 O 3 films are achieved on 1L MoS 2 with markedly improved uniformity compared to standard Al 2 O 3 ALD using TMA and H 2 O, as validated by atomic force microscopy (AFM), cross-sectional scanning transmission electron microscopy (STEM), and energy-dispersive X-ray spectroscopy (EDS). Density functional theory (DFT) calculations further provide atomistic insight into HAc-modulated Al 2 O 3 nucleation, corroborating the energetic preference of HAc for Al 2 O 3 over MoS 2 and attenuated TMA adsorption on HAc-passivated surfaces. Spatially resolved Raman spectroscopy also confirms that the HAc-modulated process preserves the structural integrity of 1L MoS 2 , with only minimal strain and doping perturbations observed after dielectric deposition. This SMI-modulated approach offers a broadly applicable framework for controlling ALD nucleation across various inhibitors, ALD chemistries, and 2D materials, opening opportunities for reliable dielectric integration in next-generation nanoelectronics.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Engendering Long-Term Air and Light Stability of a TiO2-Supported Porphyrinic Dye via Atomic Layer Deposition

Organic and porphyrin-based chromophores are prevalent in liquid-junction photovoltaic and photocatalytic solar-cell chemistry; however, their long-term air and light instability may limit their practicality in real world technologies. Here, we describe the protection of a zinc porphyrin dye, adsorbed on nanoparticulate TiO2, from air and light degradation by a protective coating of alumina grown with a previously developed post-treatment atomic layer deposition (ALD) technique. The protective Al2O3 ALD layer is deposited using dimethylaluminum isopropoxide as an Al source; in contrast to the ubiquitous ALD precursor trimethylalurninum, dimethylaluminum isopropoxide does not degrade the zinc porphyrin dye, as confirmed by UV vis measurements. The growth of this protective ALD layer around the dye can be monitored by an in-reactor quartz crystal microbalance (QCM). Furthermore, greater than 80% of porphyrin light absorption is retained over month of exposure to air and light when the protective coating is present, whereas almost complete loss of porphyrin absorption is observed in less than 2 days in the absence of the ALD protective layer. Applying the Al2O3 post-treatment technique to the TiO2-adsorbed dye allows the dye to remain in electronic contact with both the semiconductor surface and a surrounding electrolyte solution, the combination of which makes this technique promising for numerous other electrochemical photovoltaic and photocatalytic applications, especially those involving the dye-sensitized evolution of oxygen.

atomic layer deposition↗
DOE OSTI2025

Crystalline 1D Coordination Polymer Inhibitor Layer Leads to Vertical Sidewalls in Selectively Deposited ZnO on Nanoscale Patterns

Area-selective atomic layer deposition (AS-ALD) is a promising technique for the fabrication of next-generation nanoelectronics. There are two main challenges in AS-ALD: (1) achieving high selectivity of deposition on the growth regions, and (2) preventing mushrooming of the growth material onto the nongrowth regions and achieving well-defined interfaces. In this work, we use benzenethiol (BT) as an inhibitor in the selective deposition of ZnO on SiO 2 in the presence of copper with and without a native oxide (Cu/CuO x ). We observe that BT forms a monolayer on the Cu surface and a Cu-thiolate multilayer structure on CuO x . Using grazing incidence X-ray diffraction combined with simulations, we find that the multilayer structure is crystalline and composed of 1D coordination polymers of Cu-thiolate. Here, using ellipsometry and X-ray photoelectron spectroscopy, we show that the BT consumes the entirety of the CuO x during multilayer formation, allowing the multilayer thickness to be tuned by the thickness of the original oxide. Both the monolayer BT and the multilayer BT prove to be effective inhibitors of ZnO ALD, blocking nearly 500 ALD cycles, which is more than twice that achieved with other thiol inhibitors. Finally, we demonstrate that the multilayer structure can prevent mushrooming of the ALD material onto the nongrowth surface of nanoscale patterns, creating vertical sidewalls with well-defined material interfaces and providing excellent pattern transfer, even for a relatively thick deposited film. As such, these results demonstrate that BT is not only an effective inhibitor but also that its ability to form tunable multilayers makes it well-suited for highly precise nanopatterning applications.

Layers↗
DOE OSTI2022

Resolving the Heat of Trimethylaluminum and Water Atomic Layer Deposition Half-Reactions

We report that atomic layer deposition (ALD) is a surface synthesis technique that is characterized by self-limiting reactions between gas-phase precursors and a solid substrate. Although ALD processes have been demonstrated that span the periodic table, a greater understanding of the surface chemistry that affords ALD is necessary to enable greater precision, including area- and site-selective growth. We offer new insight into the thermodynamics and kinetics of the trimethylaluminum (TMA) and H 2 O ALD half-reactions with calibrated and time-resolved in situ pyroelectric calorimetry. The half-reactions produce 3.46 and 2.76 eV/Al heat, respectively, which is greater than the heat predicted by computational models based on crystalline Al 2 O 3 substrates and closely aligned with the heat predicted by standard heats of formation. The pyroelectric thin-film calorimeter offers submilisecond temporal resolution that uniquely and clearly resolves precursor delivery and reaction kinetics. Both half-reactions are observed to exhibit multiple kinetic rates, with average TMA half-reaction rates at least 2 orders of magnitude faster than the H 2 O half-reaction kinetics. Comparing the experimental heat with published computational literature and additional first-principles modeling highlights the need to refine our models and mechanistic understanding of even the most ubiquitous ALD reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Modeling Climate Change Impacts on an Arctic Polygonal Tundra: 1. Rates of Permafrost Thaw Depend on Changes in Vegetation and Drainage

Model projections of permafrost thaw during the next century diverge widely. Here we used ecosys to examine how climate change will affect permafrost thaw in a polygonal tundra at Barrow AK. The model was tested against diurnal and seasonal variation in energy exchange, soil heat flux, soil temperature ( T s ), and active layer depth (ALD) measured during 2014 and 2015, and interannual variation in ALD measured from 1991 to 2015. During RCP 8.5 climate change from 2015 to 2085, increases in T a and precipitation ( P ) to 6.2 °C and 27% above current values, and in atmospheric CO 2 concentrations ( C a ) to 763 μmol mol -1 , altered energy exchange by increasing leaf area index of dominant sedge relative to that of moss. Increased Ca and sedge leaf area index imposed greater stomatal control of transpiration and reduced soil heat fluxes, slowing soil warming, limiting increases in evapotranspiration, and thereby causing gradual soil wetting. Consequently, increases in surface T s and ALD of 2.4–4.7 °C and 21–24 cm above current values were modeled after 70 years. ALD increase was slowed if model boundary conditions were altered to improve landscape drainage. These rates were smaller than those of earlier modeling studies, some of which did not account for changes in vegetation, but are closer to those derived from current studies of warming impacts in the region. Therefore, accounting for climate change effects on vegetation density and composition, and consequent effects on surface energy budgets, will cause slower increases in T s and ALD to be modeled during climate change simulations.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Design and synthesis of model and practical palladium catalysts using atomic layer deposition

Here, we investigated the “one-batch” synthesis of model and practical palladium catalysts using atomic layer deposition (ALD). Two types of model catalysts and one type of powder-based nanocatalyst were synthesized simultaneously by ALD under viscous flow conditions. In addition, Pd/TiO 2 (110) model catalysts were prepared by the identical ALD process but under ultrahigh vacuum conditions. Because of the self-limiting surface reaction that defines ALD, the local structure of all the Pd catalysts were essentially the same as confirmed by a suite of microscopic and spectroscopic characterization techniques. A comprehensive understanding of the Pd-based catalysts was achieved by applying both surface science probes and advanced synchrotron techniques, and by strategically selecting the catalyst substrate best suited for each characterization. Both X-ray absorption spectroscopy and X-ray resonant photoelectron spectroscopy suggested that Pd only weakly interacted with the TiO 2 support. The one-batch synthesis approach facilitated by ALD can potentially bridge the “synthesis gap” between model catalysts and practical catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

ZrO 2 atomic layer deposition into Sr 0.5 Sm 0.5 CoO 3-δ –Ce 0.9 Gd 0.1 O 2-δ solid oxide fuel cell cathodes: mechanisms of stability enhancement

The application of atomic layer deposition (ALD) on solid oxide fuel cell (SOFC) cathodes has previously yielded mixed results and has been seen to depend on the ALD species, catalyst chemistry, catalyst morphology, and the conditions for deposition. Illustrated here is the effect of an ALD zirconia coating within an SOFC oxygen electrode: Sr 0.5 Sm 0.5 CoO 3- δ infiltrated into Gd-doped ceria, Ce 0.9 Gd 0.1 O 2- δ , scaffolds (SSC–GDC). Island-like ALD-ZrO 2 coatings with approximately monolayer coverage initially yield a higher electrode polarization resistance, R P , but thereafter the coated electrodes show lower R P and slower degradation. For example, after~1000 hour accelerated ageing tests carried out at 750 °C, SSC–GDC coated with ~0.3 nm of ALD-ZrO 2 showed an R P increase of 18% compared to 30% for uncoated SSC–GDC. Strontium surface segregation was not found to be a significant degradation factor. At 750 °C, a reaction between the Zr-overlayer and the SSC was observed, producing SrZrO 3 , Co 3 O 4 , and SmCoO 3 . The low R P values achieved indicate that the reactant products were thin enough to be discontinuous and thus not hinder the oxygen surface exchange process, and yet they acted as a barrier to SSC particle coarsening.

25 ENERGY STORAGE↗
DOE OSTI2021

Atomic/molecular layer deposition for energy storage and conversion

Energy storage and conversion systems, including batteries, supercapacitors, fuel cells, solar cells, and photoelectrochemical water splitting, have played vital roles in the reduction of fossil fuel usage, addressing environmental issues and the development of electric vehicles. The fabrication and surface/interface engineering of electrode materials with refined structures are indispensable for achieving optimal performances for the different energy-related devices. Atomic layer deposition (ALD) and molecular layer deposition (MLD) techniques, the gas-phase thin film deposition processes with self-limiting and saturated surface reactions, have emerged as powerful techniques for surface and interface engineering in energy-related devices due to their exceptional capability of precise thickness control, excellent uniformity and conformity, tunable composition and relatively low deposition temperature. In the past few decades, ALD and MLD have been intensively studied for energy storage and conversion applications with remarkable progress. In this work, we give a comprehensive summary of the development and achievements of ALD and MLD and their applications for energy storage and conversion, including batteries, supercapacitors, fuel cells, solar cells, and photoelectrochemical water splitting. Moreover, the fundamental understanding of the mechanisms involved in different devices will be deeply reviewed. Furthermore, the large-scale potential of ALD and MLD techniques is discussed and predicted. Finally, we will provide insightful perspectives on future directions for new material design by ALD and MLD and untapped opportunities in energy storage and conversion.

25 ENERGY STORAGE↗
DOE OSTI2014

Properties of the c-Si/Al{sub 2}O{sub 3} interface of ultrathin atomic layer deposited Al{sub 2}O{sub 3} layers capped by SiN{sub x} for c-Si surface passivation

This work presents a detailed study of c-Si/Al{sub 2}O{sub 3} interfaces of ultrathin Al{sub 2}O{sub 3} layers deposited with atomic layer deposition (ALD), and capped with SiN{sub x} layers deposited with plasma-enhanced chemical vapor deposition. A special focus was the characterization of the fixed charge density of these dielectric stacks and the interface defect density as a function of the Al{sub 2}O{sub 3} layer thickness for different ALD Al{sub 2}O{sub 3} deposition processes (plasma-assisted ALD and thermal ALD) and different thermal post-deposition treatments. Based on theoretical calculations with the extended Shockley–Read–Hall model for surface recombination, these interface properties were found to explain well the experimentally determined surface recombination. Thus, these interface properties provide fundamental insights into to the passivation mechanisms of these Al{sub 2}O{sub 3}/SiN{sub x} stacks, a stack system highly relevant, particularly for high efficiency silicon solar cells. Based on these findings, it was also possible to improve the surface passivation quality of stacks with thermal ALD Al{sub 2}O{sub 3} by oxidizing the c-Si surface prior to the Al{sub 2}O{sub 3} deposition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Redeposition in plasma-assisted atomic layer deposition: Silicon nitride film quality ruled by the gas residence time

The requirements on the material properties and growth control of silicon nitride (SiN{sub x}) spacer films in transistors are becoming ever more stringent as scaling of transistor structures continues. One method to deposit high-quality films with excellent control is atomic layer deposition (ALD). However, depositing SiN{sub x} by ALD has turned out to be very challenging. In this work, it is shown that the plasma gas residence time τ is a key parameter for the deposition of SiN{sub x} by plasma-assisted ALD and that this parameter can be linked to a so-called “redeposition effect”. This previously ignored effect, which takes place during the plasma step, is the dissociation of reaction products in the plasma and the subsequent redeposition of reaction-product fragments on the surface. For SiN{sub x} ALD using SiH{sub 2}(NH{sup t}Bu){sub 2} as precursor and N{sub 2} plasma as reactant, the gas residence time τ was found to determine both SiN{sub x} film quality and the resulting growth per cycle. It is shown that redeposition can be minimized by using a short residence time resulting in high-quality films with a high wet-etch resistance (i.e., a wet-etch rate of 0.5 nm/min in buffered HF solution). Due to the fundamental nature of the redeposition effect, it is expected to play a role in many more plasma-assisted ALD processes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗