Conventional ALD Research Articles

Low temperature (002)-oriented zinc oxide films prepared using ozone-based spatial atomic layer deposition

In this study, ZnO films are prepared at a low temperature of 150 °C by using spatial atomic layer deposition (sALD) with diethylzinc and ozone as precursor and oxidant. The ozone flow rate is varied to systematically investigate its effect on optical, structural and electrical properties. The experimental results show that the self-limiting surface reactions can occur at the low ozone flow rate of 200 sccm, confirming ALD growth mode. All the ozone flow rates lead to ZnO (002) crystalline orientation, which is difficult to be obtained for conventional water-based ALD ZnO films at the low temperature. The increased ozone flow rate results in an increased amount of oxygen vacancies, enhanced carrier concentration and a reduced stress. The resistivity and carrier concentration can be tuned in the range of 4.75–0.08 Ω-cm and (1.1–5.5) × 1018 cm−3. Finally, the sALD ZnO film on polyethylene terephthalate reveals a high stability in the film property against bending. This study is beneficial for the utilization of ZnO films in optoelectronic devices that demand the (002) preferred orientation, especially under low-temperature conditions.

Enhancing control in spatial atomic layer deposition: insights into precursor diffusion, geometric parameters, and CVD mitigation strategies

In recent years, spatial atomic layer deposition (SALD) has gained significant attention for its remarkable capability to accelerate ALD growth by several orders of magnitude compared to conventional ALD, all while operating at atmospheric pressure. Nevertheless, the persistent challenge of inadvertent contributions from chemical vapor deposition (CVD) in SALD processes continues to impede control over film homogeneity, and properties. This research underscores the often-overlooked influence of diffusion coefficients and important geometric parameters on the close-proximity SALD growth patterns. We introduce comprehensive physical models complemented by finite element method simulations for fluid dynamics to elucidate SALD growth kinetics across diverse scenarios. Our experimental findings, in alignment with theoretical models, reveal distinctive growth rate trends in ZnO and SnO2 films as a function of the deposition gap. These trends are ascribed to precursor diffusion effects within the SALD system. Notably, a reduced deposition gap proves advantageous for both diffusive and low-volatility bulky precursors, minimizing CVD contributions while enhancing precursor chemisorption kinetics. However, in cases involving highly diffusive precursors, a deposition gap of less than 100 μm becomes imperative, posing technical challenges for large-scale applications. This can be ameliorated by strategically adjusting the separation distance between reactive gas outlets to mitigate CVD contributions, which in turn leads to a longer deposition time. Furthermore, we discuss the consequential impact on material properties and propose a strategy to optimize the injection head to control the ALD/CVD growth mode.

Enhancement of Conformality of Silicon Nitride Thin Films by ABC‐Type Atomic Layer Deposition

AbstractAtomic layer deposition (ALD) is utilized for the fabrication of miniaturized electronic devices with nanometer‐scale features. However, the conventional ALD process on high‐aspect‐ratio (HAR) substrates often results in the deposition of thin films with suboptimal conformality over the depth of the trench structures. This study introduces an ABC‐type ALD of silicon nitride (SiNx) employing vapor‐deliverable tert‐butyl chloride (TBC) as a surface inhibitor. Herein, density functional theory (DFT) calculations elucidate the surface reaction mechanisms, confirming the inhibition of the Si precursor by the t‐butyl moiety. Notably, the ABC‐type ALD exhibits reduced growth per cycle relative to the conventional process while avoiding detectable carbon contamination in the SiNx thin films. Applying this process to substrates with trench structures revealed a substantial improvement in conformality following the introduction of TBC. Furthermore, the step coverage of the deposited SiNx can be modulated by adjusting TBC exposure, enabling greater film thickness at the bottom than that at the top of the trench. The proposed method of modulating ALD processes holds potential for the high‐volume manufacturing of semiconductor devices with HAR structures.

Machine learning-based exploration of molecular design descriptors for area-selective atomic layer deposition (AS-ALD) precursors.

Area-selective atomic layer deposition (AS-ALD) is a thin film deposition technique developed using conventional ALD by considering the surface chemical nature of the substrate. Selecting appropriate precursors is a critical step in developing an efficient AS-ALD process with high deposition selectivity. However, the current efficiency of research on viable AS-ALD precursors is limited because of the absence of theoretical design rules for precursor chemical structures. In this study, our objective is to propose molecular design principle for precursors for AS-ALD, particularly focusing on achieving high deposition selectivity of oxides on diverse substrates. Current preliminary results suggest that ML-based prediction model may provide a fundamental molecular-level understanding of the reactivity of metal oxide precursors, that can be useful for efficient selection of suitable precursors for AS-ALD. We employ density functional theory (DFT) calculations and machine learning (ML) techniques to analyze the relationship between the structure and the surface reactivity of the precursor. Considering DFT calculation data (M06L/def2-tzvp, Gaussian 09 and Orca 4.0) and information on precursor structures, artificial neural networks (ANN, neuralnet, R) are applied to identify critical descriptors of the AS-ALD process. Furthermore, we utilize this ANN model to predict precursor reactivity according to surface terminations.

Growth chemistry and electrical performance of ultrathin alumina formed by area selective vapor phase infiltration

Abstract 1 1 Commercial equipment is identified in this report in order to specify the experimental procedure adequately and does not imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the equipment identified is necessarily the best available for the purpose. The growth chemistry and electrical performance of 5 nm alumina films, fabricated via the area-selective vapor phase infiltration (VPI) of trimethylaluminum into poly(2-vinylpyridine), are compared to a conventional plasma enhanced atomic layer deposition (PEALD) process. The chemical properties are assessed via energy dispersive X-ray spectroscopy and hard X-ray photoelectron spectroscopy measurements, while current – voltage dielectric breakdown and capacitance – voltage analysis is undertaken to provide electrical information of these films for the first time. The success and challenges in dielectric formation via polymer VPI, the compatibility of pyridine in such a role, and the ability of the unique and rapid grafting-to polymer brush method in forming coherent metal oxides is evaluated. It was found that VPI made alumina fabricated at temperatures between 200 and 250 °C had a consistent breakdown electrical field, with the best performing devices possessing a к value of 5.9. The results indicate that the VPI approach allows for the creation of alumina films that display dielectric properties of a comparable quality to conventional PEALD grown films. • Dielectrics grown by VPI of poly(2-vinylpyridine) electrically characterised for the first time. • Best performing VPI-made Al 2 O 3 competes in performance to conventional ALD. • IV breakdown reveals a high consistency in electrical properties is possible. • Process is low temperature and compatible in area selective deposition. • CV and HAXPES analysis reveal the next challenges for industry integration.

ZIF-Based Metal-Organic Frameworks for Cantilever Gas Sensors

Among the different gas sensing platforms, cantilever-based sensors have attracted considerable interest in recent years thanks to their ultra-sensitivity and high-speed response. The gas sensing mechanism in a dynamic cantilever sensor is based on its resonance frequency shift upon adsorption of a gas molecule on the sensor. In order to sensitize the surface of a cantilever, a sensitive receptor material with large surface area is required. Metal-organic frameworks (MOFs) are a class of nanoporous crystalline materials composed of metal ions coordinated to organic linkers. MOFs are promising for gas sensing applications as they have large surface area, rich porosity with adjustable pore size and excellent selective adsorption capability for various gasses.[1] Zeolite imidazole frameworks (ZIFs) are a class of MOFs where metals with tetrahedral coordination (i.e. Zn, Co, Fe, Cu) are the central node and the ligands are imidazolate-based organic molecules.In this work, we developed a ZIF-based thin film for dynamic cantilever gas-sensing applications. We employed a novel atmospheric pressure spatial atomic layer deposition (AP-SALD)[2][3] technique to deposit a ZnO sacrificial layer on the silicon cantilevers. This technique allows the deposition of high-quality films at atmospheric pressure, faster than conventional ALD. The ZnO layer was then converted to a particular ZIF film with desired porosity and size, through a MOF-CVD process.[4] A gas-sensing bench setup was developed for the cantilever actuation and read-out. We present the chemical and morphological properties of the ZIF, as well as the frequency response of the sensor to various gases. The device showed reliable sensitivity to humidity, CO2 and several VOCs.

Formation of Free Hydrogen Gas By Annealing ALD-Al2O3/Si Stacked Structure

1. IntroductionAtomic layer depositions (ALD) of Al2O3 films are very essential technique to realize next generation electronic devices thanks to their high-k properties [1]. However, ALD-Al2O3 films usually suffer blistering during thermal treatments, which have caused serious problems for decades in the field of device fabrication [2]. Many groups have studied the cause of this phenomenon, and various models have been proposed. such as, stress at the interface between Al2O3 and Si [3], diffusion of Si atoms at the interface[4], residual H2O in the film after the ALD process [5], and aggregation of hydrogen atoms at the Al2O3/Si interface [6], and so on. However, the actual mechanism has hitherto remained unclear due to a lack of conclusive evidence. Here, in this study, we have tried to reveal the origin of this phenomenon using spectroscopic measurements [7]. As a result, we have succeeded in directly identifying the gas inside the blisters, which can be a concrete evidence to reveal the roots of a phenomenon that has long been obscured.2. Experimental ProcedureIn the experiment, (100) oriented Si substrates with resistivity of 0.1-0.5 W∙cm were carried out. After cleaning the substrates by acetone, sulfuric-acid hydrogen-peroxide mixture solution, and hydrofluoric acid solution, all the substrates were loaded into ALD chamber which was heated up to 300oC. Then, Al2O3 layer with ~108 nm thickness was deposited on the substrates with conventional thermal ALD process using trimethylaluminum (TMA) and H2O as precursor gasses. After deposition, samples were annealed in rapid thermal annealing (RTA) furnace for 5 min with 400 – 1000 oC at N2 ambient. Finally the samples were characterized by laser microscopy, field emission scanning electron microscopy (FE-SEM), spectroscopic ellipsometry, and Raman spectroscopy.3. Results and DiscussionsFigs. 1(a) and 1(b) show typical microscopic image of sample before, and after RTA (500oC, 5 min), respectively. We can clearly see that several blisters appear by annealing the samples, while there was no such sign before annealing. From the microscopic observations, we have summarized density of blisters as a function of RTA temperature in Fig. 2. Here, we can clearly see that by increasing RTA temperature, blister density increases, which is largely consistent with a previous result reported by O. Beldarrain et al, where 400-cycle Al2O3 layers were grown at 200 oC.To discuss the origin of the blister, we have conducted cross-sectional SEM observations of the formed blisters. Fig. 3 shows a typical SEM image of a blister after annealed at 500oC. The cross-sectional SEM observations clearly show that the blisters are completely hollow underneath. The surface of the flat Si substrate can also be seen under the blister, indicating that the upper Al2O3 film has completely delaminated from the interface between Si and Al2O3. From these results, we have speculated that blistering of Al2O3 after annealing is due to outgassing from the Al2O3/Si interface. Here, we came up with an idea that by identifying the gas inside the blisters, we can clarify the cause of this phenomenon.To identify the content inside blisters, Raman spectroscopy was carried out. The 532 nm wavelength laser used for Raman measurements can pass completely through Al2O3, making it possible to measure the gas inside without destroying the blisters. Fig. 4 shows a typical result of the Raman measurement of a blister of a sample after RTA (500oC). Here, as a result, characteristic spectra with peaks at positions ~4126, ~4144, ~4156, and ~4162 cm-1 were successfully observed. These four peaks can be assigned as peaks due to the difference in the rotational-quantum-number (J) of H2 as shown in Fig. 4, which is typical spectra of free H2 gas. These results provide evidence that blister formation is caused by the generation of hydrogen gas from the Al2O3/Si interface, a finding that is of great importance in clarifying the physics of blister formation mechanisms.In the presentation, we will also present details on the physics of hydrogen gas generation and methods to suppress blister formation.[References][1] R. Zhang, et al., IEEE Trans. Electron Devices 59, 335-341, (2012).[2] G Dingemans, et al., J. Vac. Sci. Technol. A, 30, 040802, (2012).[3] J. Thurn., et al., J. Mater. Sci. 39, 4799, (2004)[4] M. Broas, et al., Appl. Phys. Lett. 111, 141606, (2017)[5] O. Beldarrain, et al., J. Vac. Sci. Technol. A, 31, 01A128 (2013)[6] D. G. Xie, et al., Nat. Mater., 14, 899, (2015).[7] R. Matsumura, et al., accepted to ACS Applied Materials & Interfaces, https://doi.org/10.1021/acsami.1c20660 Figure 1

High‐Throughput Atomic Layer Deposition of P‐Type SnO Thin Film Transistors Using Tin(II)bis(tert‐amyloxide)

AbstractSpatial atomic layer deposition (sALD) of p‐type SnO is demonstrated using a novel liquid ALD precursor, tin(II)‐bis(tert‐amyloxide), Sn(TAA)2, and H2O as the coreactant in a process which shows an increased deposition rate when compared to conventional temporal ALD. Compared to previously reported temporal ALD chemistries for the deposition of SnO, deposition rates of up to 19.5 times higher are obtained using Sn(TAA)2 as a precursor in combination with atmospheric pressure sALD. Growths per cycle of 0.55 and 0.09 Å are measured at deposition temperatures of 100 and 210 °C, respectively. Common‐gate thin film transistors (TFTs), fabricated using sALD with Sn(TAA)2 result in linear mobilities of up to 0.4 cm2 V–1 s–1 and on/off‐current ratios, IOn/IOff > 102. The combination of enhanced precursor chemistry and improved deposition hardware enables unprecedently high deposition rate ALD of p‐type SnO, representing a significant step toward high‐throughput p‐type TFT fabrication on large area and flexible substrates.

Exploring argon plasma effect on ferroelectric Hf0.5Zr0.5O2 thin film atomic layer deposition

The doped/alloyed HfO2 and ZrO2 thin films revolutionized not only the field of ferroelectric physics but also various ranges of device applications. Especially when the two oxides are combined in an 1:1 ratio, the ferroelectric polarization of the material became the most distinctive. Many researchers have investigated various different process conditions such as controlling Hf0.5Zr0.5O2 (HZO) film thickness and modifying different metal electrodes. Here, we explored the effect of additional Ar plasma treatment to the HZO film. The additional Ar plasma was exposed to the plasma-enhanced atomic layer deposition (PEALD) HZO for this study. Then, the sample was compared with a conventional PEALD and thermal ALD HZO films. By understanding the polarization–electric field (P–E), current–electric field (I–E), and electrical breakdown characteristics of the different samples, it was found that the Ar plasma treatment can control the degree of ferroelectric and antiferroelectric phases of HZO film.

Large enhancement of photocatalytic activity in ZnO thin films grown by plasma-enhanced atomic layer deposition

In this work, we present a large, tenfold enhancement in the photocatalytic activity of thin ZnO films grown by plasma-enhanced atomic layer deposition (PE-ALD) at 100 °C, compared to values obtained for thin ZnO films deposited by a conventional thermal ALD method at the same temperature. Thus, we have demonstrated that we can deposit thin ZnO films using the PE-ALD method both at low temperatures and with a high photocatalytic ability. A number of structural (SEM, EDX, HRTEM, GIXRD, XRR, XPS, SIMS) and optical (UV-Vis, PL) experimental techniques have been employed to elucidate a possible physical origin of the observed remarkable difference in the photocatalytic activity of thin ZnO films grown by the PE-ALD method compared to those grown by the thermal ALD method.

Improved Perovskite Solar Cell Performance by High Growth Rate Spatial Atomic Layer Deposited Titanium Oxide Compact Layer

In this study, titanium dioxide (TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) films are prepared using spatial atomic layer deposition (sALD) as an additional compact layer of tin oxide (SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) electronic transport layer-based perovskite solar cells. The experimental results show that the deposition of sALD TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> films on the fluorine-doped tin oxide substrate improves the haze at mid-long wavelengths, compensating the optical loss caused by the absorption of the TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer in short-wavelengths. Compared to conventional cells, the insertion of the sALD TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> compact layer regardless the thickness shows significantly improved open-circuit voltage, indicating the enhanced hole blocking ability as evidenced by the reduced reverse saturation current. In addition, the change in TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thickness is found to have impacts on short-circuit current, fill factor and hysteresis of the devices. The optimal sALD TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thickness of 10 nm leads to the best cell conversion efficiency of 20.1%, approximately improved by 6% compared to that of the conventional cells. Compared to conventional ALD techniques and other methods, the sALD which does not require vacuum system has the pinhole-free, low-cost, very fast and simple processes, demonstrating the great potential of sALD films for applications in perovskite solar cells.

Atmospheric pressure atomic layer deposition of iron oxide nanolayer on the Al2O3/SiO2/Si substrate for mm-tall vertically aligned CNTs growth

Atmospheric pressure atomic layer deposition (AP-ALD) of iron oxide, as a catalyst for water-assisted chemical vapor deposition (WA-CVD) growth of vertically aligned carbon nanotubes (VA-CNTs), was studied. Fe2O3 film was deposited on the porous Al2O3/SiO2/Si substrate using ferrocene and O2 as precursors. The self-liming film growth was obtained at the temperature window of about 180–250 °C with the optimum dosing and purging duration of about 20 min. The rather longer dosing time here compared to the conventional ALD is attributed to the high pressure as well as high porosity of the substrate. Considering the lower deposition rate at the beginning of the growth, it is suggested that the substrate-inhibited growth mode takes place in this work. The grown films have been characterized by SEM, AFM, Raman, and XRR. Raman spectroscopy peaks were consistent with the formation of Fe2O3. SEM images showed that the uniform coating of Fe2O3 follows the Volmer–Weber growth mode. The catalyst thickness-dependent growth of VACNTs revealed that the deposition through 12 cycles at 250 °C provides sufficient thickness, which resulted in the growth of mm-tall VA-CNTs within a relatively short time of WA-CVD. The changes in the catalyst, i.e. surface roughness and particle size, as a function of WA-CVD time were investigated. The time-dependent evolutions were mainly due to the subsurface diffusion and Ostwald ripening that ultimately led to the growth termination of CNTs.

Area-Selective Atmospheric-Pressure Spatial ALD of SiO2 Using Interleaved Back-Etch Steps Yielding Selectivity > 10 Nanometer

Area-selective atomic layer deposition (AS-ALD) has great potential in reducing cost by maskless device manufacturing of patterned layers. Still, in this new bottom-up approach the selectivities currently obtained for film growth on patterned growth areas vs. that on the non-growth areas are often very limited. Also the substrate throughput values for conventional low-pressure ALD is too low for industrial acceptance (1,2). In this work we present a process for AS-ALD of SiO2 using intermittent plasma etch-back steps to increase the selectivity above 10 nm film thickness (3). In addition, the deposition process itself is performed in a spatial ALD reactor at atmospheric pressure which allows for achieving high throughput (4). AS-ALD of SiO2 on a substrate with pre-patterned SiO2 and ZnO areas was demonstrated using a chemo-selective inhibitor that chemisorbs preferentially on the non-growth area (ZnO) while allowing the deposition of SiO2 on the growth area (SiO2). In order to maximize the process selectivity, a blanket fluorocarbon plasma etch-back step was interleaved after every 110 ALD cycles. This way, selective SiO2 deposition up to ~ 30 nm film thickness was demonstrated (Fig. 1). Furthermore, X-ray Photoelectron Spectroscopy was carried out to verify the selectivity of the process: no Si was detected (detection limit 0.3 at. %) on the non-growth area, demonstrating the high selectivity of the process. The process presented here combines selective inhibitor chemisorption, plasma-based spatial ALD with high deposition rates and plasma etch-back steps to correct for selectivity loss. This approach is compatible with roll-to-roll and sheet-to-sheet concepts and can therefore enable high-throughput AS-ALD on large-area and flexible substrates. ----------------------------------------------------------------------------------------------------------------------------------------------------------------

Infrared and Optical Emission Spectroscopy Study of the Surface Chemistry in Atmospheric-Pressure Plasma-Enhanced Spatial ALD of Al2O3

In the past decade, atmospheric-pressure spatial atomic layer deposition (AP-SALD) has gained momentum as a fast deposition technique in thin-film manufacturing [1]. The key benefits of conventional ALD, such as superior control of layer thickness, conformality and homogeneity, in addition to the high throughput enabled by the spatial separation of the half-reactions and the more cost-effective processing at atmospheric pressure, make AP-SALD an interesting option for industrial large-area applications. Finally, the use of atmospheric pressure plasmas as co-reactants enables to rapidly deposit high-quality, dense films at relatively low temperatures [2]. Despite its industrial potential, the further advancement of atmospheric-pressure plasma-enhanced spatial ALD processing still lacks a detailed understanding of the underlying plasma physics and chemistry. Here, effective ALD metrology techniques are of prime importance to obtain more detailed insights into the nature of the process with the aim to improve process performance and thus to open up new industrial application fields. However, due to the very nature of the spatial concept, monitoring AP-SALD processes is rather challenging: especially in the case of close-proximity systems the substrate is typically at ~100 μm distances from the gas injection head. In this work, we employed optical emission spectroscopy (OES) and infrared spectroscopy on effluent plasma gases as diagnostics tools to study the basic chemistry of the AP-SALD process of Al2O3 films grown from Al(CH3)3 and Ar-O2 plasma in a rotary lab-scale reactor (see Fig. 1 and ref. 1). We identified the main reaction products and studied their behavior as a function of the exposure time to the precursor to verify the ALD layer-by-layer growth characteristics. The results show that using spatial separation of the ALD half-reactions and atmospheric pressure plasma as the reactant gives rise to a complex underlying chemistry (see Fig. 2). Infrared absorbance spectra show CO, CO2, H2O and CH4 as the main ALD reaction by-products originating from 1) combustion-like reactions of the methylated surface with oxygen plasma radicals and ozone, and 2) a concurrent latent thermal component related to the substrate. Moreover, CH2O and CH3OH are identified as ALD reaction by-products either formed at the surface or in the plasma by electron-induced dissociation. The investigated trends in CO2, CO and CH4 formed as a function of the exposure time confirm a self-limiting ALD behavior. Finally, the OES results corroborate that, as soon as the plasma-enhanced SALD process takes place, emission from OH and CH arises while excited oxygen species are being consumed. -------------------------------------------------------------------------------------------------------------------------------------------------------------------- References P. Poodt, A. Lankhorst, F. Roozeboom, C. Spee, D. Maas and A. Vermeer, ‘High-speed atomic layer deposition of aluminum oxide layers for solar cell passivation’, Adv. Mater., 22, 3564 - 3567 (2010).M.A. Mione, I. Katsouras, Y. Creyghton, W. van Boekel, J. Maas, G. Gelinck, F. Roozeboom, and A. Illiberi, ‘Atmospheric Pressure Plasma Enhanced Spatial ALD of ZrO2 for Low-Temperature, Large-Area Applications’, ECS Journal of Solid State Science and Technology, 6 (12) N243-N249 (2017), and refererences therein. -------------------------------------------------------------------------------------------------------------------------------------------------------------------- Figure 1

Fast-Charging All-Solid-State 3D Li-Ion Battery with Ultra-Thin Lipon and High-Capacity Electrodes Using Large-Area Atmospheric-Pressure Spatial ALD

The key challenges in next-generation all-solid-state Li-ion battery technology are related to the energy and power densities required, fast charging constraints, battery lifetime, while keeping the cost low by high-volume manufacturing. Currently, EVs are based on Li-ion batteries that often utilize highly flammable and toxic components such as liquid organic electrolyte, thus imposing a potential threat in case of failure. There is high pressure on developing batteries that are safer, smaller, and cheaper. Here, we report on innovative materials and architectural approaches that have the potential to disrupt current Li-ion battery technology, especially by combining high-capacity with high charging/discharging rates. We aimed at improving 3D battery performance by using large area atmospheric pressure spatial atomic layer deposition (sALD) for further tuning the electrode and electrolyte layers at the nanometer-scale. Apart from enabling high charge/discharge rates, 3D electrode architectures pave the way for the use of high-capacity materials without long-term cycling challenges. We will show the potential of the intrinsically safe 3D all-solid-state batteries that can be extended to energy densities required for automotive (850 Wh/l and 375 Wh/kg at cell level). However, novel architectures demand newer processing techniques, especially for conformal layer stacks over 3D structures. In this regard, we will present the results on high-rate 3D Li-ion battery electrodes coated using our patented sALD technology, which enables charging times below 10 minutes. Next, we will discuss the first-ever sALD-based LiPON electrolyte material, deposited at least 10x faster than the current technologies using conventional ALD systems, and exhibiting high Li-ion conductivity > 10-7 S/cm and very low electronic conductivity (< 10-12 S/cm). The LiPON layers are pinhole-free and demonstrated to be cycled without shorts. Such electrolytes are also relevant for the development of protection layers in wet electrolyte-based lithium ion batteries, as well as for enabling thin-film planar and 3D solid-state batteries with ultrathin electrolyte layers (few 10’s of nanometers). Highlighted during the presentation will also be the attribute of the sALD technique to produce conformal and upscalable coatings that can be applied in roll-to-roll processing using metal foils to further enable the innovative and cost-effective 3D battery layers.

Growth behavior and film properties of titanium dioxide by plasma-enhanced atomic layer deposition with discrete feeding method

Titanium dioxide (TiO2) films were deposited by plasma enhanced atomic layer deposition (PE-ALD) system using tetrakis-dimethylamido-titanium (TDMAT) at 250 °C. We applied a new source feeding method, known as Discrete Feeding Method (DFM), to PE-ALD TiO2 process for comparing the deposition rate, the physical and electrical film properties with the films deposited by conventional ALD method. Various analytical studies were carried out to investigate the change of TiO2 thin film characteristics due to DFM application. As a result, the optimal process condition was obtained with high physical properties and productivity while keeping electrical characteristics equivalent to those of the conventional ALD condition.

Toward 3D Thin-Film Batteries: Optimal Current-Collector Design and Scalable Fabrication of TiO2 Thin-Film Electrodes

Three-dimensional (3D) thin-film solid-state batteries are an interesting concept for microstorage, promising high footprint capacity, fast charging, safety, and long lifetime. However, to realize their commercialization, several challenges still need to be overcome. In this work, we focus on two issues: the conformal coating and the high throughput deposition of thin-film layers. First, to facilitate conformal deposition, a design based on 3D micropillars is chosen. Although such a design has been suggested in the past, we calculate for the first time what (footprint) capacities can be expected when using fully optimized pillar geometries while taking practical manufacturability into consideration. Next, spatial atomic layer deposition (S-ALD) is investigated as a scalable and conformal deposition technique. As proof-of-concept, 100 nm Cl-doped am-TiO2 thin-film electrodes are deposited by S-ALD on TiN-coated silicon micropillars. The influence of deposition parameters (i.e., exposure time and temperature) on the conformality and uniformity across the micropillar substrate is investigated. The results are discussed in terms of precursor diffusion and depletion, which is supported by an analytical model developed for our micropillar array. Furthermore, the Li-ion insertion properties of 3D electrodes fabricated by S-ALD and conventional ALD are compared. This research highlights the challenges and promises of 3D microbatteries and guides future S-ALD development to enable conformal and high-throughput thin-film deposition.

Deposition of Copper Nanofilms by Surface-Limited Redox Replacement of Underpotentially Deposited Lead on Polycrystalline Gold

Electrochemical atomic layer deposition (E-ALD) of copper on polycrystalline gold is a promising method to achieve highly reproducible nanofilms. Cu films of more than 30 nm were deposited by the repetitive execution of underpotential deposition (UPD) of lead and a subsequent surface limited redox replacement by Cu. Both steps were carried out in the same solution. The method enables, in contrast to conventional gas phase ALD, the deposition of layers with different height on the same substrate. Deposit growth in this one-pot system was monitored in-situ with an electrochemical quartz crystal microbalance. Film thickness, measured by optical profilometry, was compared to the number of deposition cycles and indicated a highly linear dependency. Obtained layers were characterized by means of atomic force and scanning electron microscopy and showed a slight roughening with almost no increase in the effective surface area. Energy dispersive X-ray measurements confirmed the purity of deposited Cu nanofilms. It was shown, that even with a simple setup, the described method allows the reproducible deposition of Cu on polycrystalline Au.

New Process Concepts Towards Area-Selective Atomic Layer Deposition and Atomic Layer Etching of Zinc Oxide

Area-Selective Atomic Layer Deposition, AS-ALD, can be initiated by local area-activation1,2 or -deactivation.3 We studied the maskless growth of ZnO from diethyl zinc and water. The method is based on the different nucleation delays that arise from precursor adsorption on OH-terminated versus that on H-terminated Si-substrate. TEOS (tetraethyl orthosilicate) and H2O were used to deposit a SiO2 seed layer by EBID (e-beam-induced deposition) in a pattern of 500x500 nm2 dots on H-terminated a-Si:H substrate. After this local activation the substrate was coated with a ZnO film in a conventional ALD reactor using 80 cycles of diethyl zinc and water vapor. In situ spectroscopic ellipsometry (Fig. 1), SEM, cross-sectional TEM and energy dispersive X-ray spectroscopy (EDX) showed good areal selectivity with ZnO growth only occurring on the SiO2 dots. This observation was corroborated by Density functional theory calculations suggesting a kinetically hindered surface reaction between diethyl zinc and H-terminated Si. Atomic Layer Etching, ALE, was also tested on a ZnO case. Current ALE technology is emerging in both thermal, isotropic and plasma-based, anisotropic approaches.4 In this presentation we will demonstrate a plasma-assisted ALE-process driven by radicals, and therefore being isotropic. The ALE-process was tested at temperatures between 150 and 250 °C. We used alternating doses of acetylacetone (Hacac) and O2-plasma intermitted by Ar-purging. The ZnO-layer thickness as measured by spectroscopic ellipsometry decreased linearly with the number of cycles. In a synergy test, we proved that only the alternated dosing of Hacac and O2-plasma caused ZnO etching, whereas Hacac and O2-plasma alone did not (Fig. 2). Preliminary infrared studies suggest that Hacac forms volatile complexes by metal oxide surface chelation (e.g. Zn(acac)2), whereas the O2-plasma step removes non-reactive Hacac fragments to refresh the surface for the next etching cycle.5 TEM- and XPS-inspection indicated no damage of the ZnO surface, good preservation of the ZnO-stoichiometry throughout the etching process, and no distinct contamination. Furthermore, we demonstrated this ALE-process to be selective over SiO2. We believe that this novel plasma-assisted ALE-concept can be extended to several other materials. [1] A. J. M. Mackus et al., Nanoscale, 4, 4477 (2012). [2] R. Chen et al., Adv. Mater., 18, 1086 (2006). [3] A. Mameli et al., Chem. Mater. 29, 921 (2017). [4] D. R. Zywotko, et al., Chem. Mater. 29, 1183 (2017). [5] M. A. George, et al., J. Electrochem. Soc., 143, 3257 (1996). Figure 1

Electrical Properties of Al2O3 Films Grown by the Electron Cyclotron Resonance Plasma-Enhanced Atomic Layer Deposition (ECR-PEALD) and Thermal ALD Methods

Aluminum-oxide(Al2O3) thin films were deposited by electron cyclotron resonance plasma-enhanced atomic layer deposition at room temperature using trimethylaluminum(TMA) as the Al source and O2 plasma as the oxidant. In order to compare our results with those obtained using the conventional thermal ALD method, Al2O3 films were also deposited with TMA and H2O as reactants at 280 oC. The chemical composition and microstructure of the as-deposited Al2O3 films were characterized by X-ray diffraction(XRD), X-ray photo-electric spectroscopy(XPS), atomic force microscopy(AFM) and transmission electron microscopy(TEM). Optical properties of the Al2O3 films were characterized using UV-vis and ellipsometry measurements. Electrical properties were characterized by capacitance-frequency and current-voltage measurements. Using the ECR method, a growth rate of 0.18 nm/cycle was achieved, which is much higher than the growth rate of 0.14 nm/cycle obtained using thermal ALD. Excellent dielectric and insulating properties were demonstrated for both Al2O3 films.