Spatial Atomic Layer Deposition System Research Articles

Enhancing Internal and External Stability of Perovskite Solar Cells Through Polystyrene Modification of the Perovskite and Rapid Open‐Air Deposition of ZnO/AlOx Nanolaminate Encapsulation

In this study, the internal and external stabilities of a p–i–n methylammonium lead iodide perovskite solar cell (PSC) are improved. Polystyrene (PS) is introduced into the perovskite layer to form a cross‐linked polymer–perovskite network, which enhances the nucleation and growth of the perovskite grains. Moreover, for the first time, 60 nm thick ZnO/AlOx nanolaminate (NL) thin‐film encapsulation (TFE) is deposited directly on the PSC using an atmospheric‐pressure (AP) spatial atomic layer deposition system operated in AP spatial chemical vapor deposition (AP–SCVD) mode. The rapid nature of AP–SCVD enables encapsulation of the PSCs in open air at 130 °C without damaging the perovskite. The PS additive improves the performance and internal stability of the PSCs by reducing ion migration. Both the PS additive and the ZnO/AlOx NL TFEs improve the external stability under standard test conditions (dark, 65 °C, 85% relative humidity [RH]) by preventing water ingress. The number and thickness of the ZnO/AlOx NL layers are optimized, resulting in a water–vapor transmission rate as low as 5.1 × 10−5 g m−2 day−1 at 65 °C and 85% RH. A 14‐fold increase in PSC lifetime is demonstrated; notably, this is achieved using PS, a commodity‐scale polymer, and AP–SCVD, a scalable, open‐air encapsulation method.

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.

Effect of different oxygen precursors on alumina deposited using a spatial atomic layer deposition system for thin-film encapsulation of perovskite solar cells

An atmospheric-pressure spatial atomic layer deposition system operated in atmospheric-pressure spatial chemical vapor deposition conditions is employed to deposit alumina (AlO x ) thin films using trimethylaluminum and different oxidants, including water (H2O), hydrogen peroxide (H2O2), and ozone (O3). The impact of the oxygen precursor on the structural properties of the films and their moisture-barrier performance is investigated. The O3-AlO x films, followed by H2O2-AlO x , exhibit higher refractive indexes, lower concentrations of OH− groups, and lower water-vapor-transmission rates compared to the films deposited using water (H2O-AlO x ). The AlO x films are then rapidly deposited as thin-film-encapsulation layers on perovskite solar cells at 130 °C without damaging the temperature-sensitive perovskite and organic materials. The stability of the p–i–n formamidinium methylammonium lead iodide solar cells under standard ISOS-D-3 testing conditions (65 °C and 85% relative humidity) is significantly enhanced by the encapsulation layers. Specifically, the O3-AlO x and H2O2-AlO x layers result in a six-fold increase in the time required for the cells to degrade to 80% of their original efficiency compared to un-encapsulated cells.

WS2 and WS2-ZnO Chemiresistive Gas Sensors: The Role of Analyte Charge Asymmetry and Molecular Size.

We investigate the interaction of various analytes (toluene, acetone, ethanol, and water) possessing different structures, bonding, and molecular sizes with a laser-exfoliated WS2 sensing material in a chemiresistive sensor. The sensor showed a clear response to all analytes, which was significantly enhanced by modifying the WS2 surface. This was achieved by creating WS2-ZnO heterojunctions via the deposition of ZnO nanoparticles on the WS2 surface with a high-throughput, atmospheric-pressure spatial atomic layer deposition system. Water and ethanol produced a much higher response compared to acetone and toluene for both the WS2 and WS2-ZnO sensing mediums. We resolved that the charge-asymmetry points in analyte molecules play a key role in determining the sensor response. High charge-asymmetry points correspond to highly polar bonds (HPBs) in a neutral molecule that have a high probability of interaction with the sensing medium. Our results indicate that the polarity of the HPBs primarily dictates the interaction between the analyte and sensing medium and consequently controls the response of the sensor. Moreover, the size of the analyte molecule was found to affect the sensing response; if two molecules have the same HPBs and are exposed to the same sensing medium, the smaller molecule is likely to produce a higher and faster response. Our study provides a comprehensive picture of analyte-sensor interactions that can help in advancing semiconductor gas sensors, including those based on two-dimensional materials.

Demonstration of Resistive Pt Temperature Sensors Directly Printed Using Novel Atomic-Layer 3D Printer

This case study demonstrates resistive Pt temperature sensors fabricated by a novel Atomic Layer 3D-printer, a revolutionary rapid prototyping tool utilizing a combination of atomic layer deposition (ALD), microfluidics and high precision 3D printing [1], first time introduced at AVS ALD 2020 [2], and also discussed in detail in the ECS 2021 G01 symposium [3]. The printed sensors are characterized and compared to a thin film sensor made using conventional (physical vapor deposition, lithography) methods and also to a Pt100 standard.ALD works like a chemical vapor deposition (CVD) but the precursors react with the substrate one at a time, in a sequential, self-limiting manner, offering thickness control on the level of atomic layers. Combining ALD and 3D printing, the Atomic Layer 3D-printer allows for deposition of thin films with controllable thickness in the sub-nm range in a pre-programmed X-Y pattern, with no need for lithography or additional patterning, on a wide variety of substrates.The printer nozzle moves relative to the substrate in a highly controlled manner (in this case ~2 mm/s). The nozzle is a miniature spatial ALD system where the precursor (MeCpPtMe3 in this case) flows out of the center of the nozzle, surrounded by a concentric rings of vacuum and a reactant gas, in this case ozone (O3). The result is an area-selective ALD, where each nozzle pass over the substrate equals to one ALD cycle, with a typical deposition rate of ~0.9 nm/cycle.In this study, resistive Pt temperature sensors were fabricated on the SiO2/Si substrates by printing >2 mm long Pt-wires of different thicknesses (approx. range 10-40 nm thick) using 100-500 ALD cycles at 200, 225 and 250 °C, where the width of the wires (~400 µm) was defined by the used nozzle geometry (Fig. 1 shows the fabrication flow).Morphology studies of the Pt surface by scanning electron microscopy (Fig. 2) revealed that the film growth in the initial stages follows island-like nucleation, eventually becoming progressively denser with increasing number of ALD cycles. The Pt wire deposited using 200 cycles (nozzle passes) consist of interconnected network of Pt grains, while the one made using 400 cycles (~ 30 nm thick) consists of a continuous polycrystalline Pt film. This growth mechanism is typical for this thermal ALD (Pt+O3) process [4].Sensors were annealed at 600 °C in N2 to ensure temperature stability, and equipped with Au contact pads 2 mm apart (made by e-beam PVD through a shadow mask) for electrical characterization. The resistance was measured in the 25-400 °C range (selected characteristics shown in Fig. 3a), as well as in cryogenic temperatures down to 3 K (not shown here).Interestingly, higher temperature sensitivity S (Fig. 3b) was found for samples made by 200 ALD cycles, with a morphology of a network of interconnected Pt grains.The comparison of temperature coefficients of resistivity α (normalized sensitivity, Fig. 3c) clearly shown that the printed ALD Pt demonstrate better temperature sensing characteristics than the conventional 30 nm e-beam PVD Pt thin film, and is comparable also to the Pt100 standard.We will also discuss sensors printed on corrugated surfaces, i.e. black Si and Si gratings.The resistive Pt temperature sensors demonstrated in this study fabricated by a novel Atomic Layer 3D-printer are suitable for rapid printing in small-footprint areas where temperature sensing is required. Targeted, low temperature deposition with no need for lithographic masks or additional patterning paves the way for myriads of applications, e.g. on a chip, or in a battery. The characteristics of these sensors are shown to be comparable to a thin film sensor fabricated using conventional processing, as well as a Pt100 standard, thanks to high film quality delivered by the ALD process.We acknowledge the support of the H2020-EU ATOPLOT project (grant ID: 950785).

Computational fluid dynamics modeling of spatial atomic layer deposition on microgroove substrates

Spatial atomic layer deposition (ALD) is a promising high-throughput technique capable of producing ultrathin films on large substrates. Compared to flat wafers, deposition on substrates with microstructures has a wider range of applications such as photovoltaic cells, electronics, flexible displays, etc. However, spatial ALD on microstructure substrates is a complex and strong-coupled process of fluid flow, heat and mass transfer, as well as chemical reactions. The fluid dynamics and the precursor distribution in spatial ALD are of great importance to obtain conformal growth with high throughput. In this study, a two-dimensional model coupling computational fluid dynamics with chemical kinetics is established to quantitatively explore the effect of microgroove structures on the fluid dynamics, precursor distribution and film conformality in an atmospheric spatial ALD system. Slip boundary condition is adopted to model the slip flow regime in the micro-gap between the injector and the substrate surface, and dynamic layering method is implemented to simulate an entire ALD cycle with the in-line movement of the substrate. Results show that while the flow field is very smooth with a flat substrate, vortices always exist in the micro-gap with microgroove substrates. Due to the angle differences between the flow direction and the vertical microstructure surface, the inflow and outflow of precursors and purging gas are prevented at the microgroove corners. A relatively lower moving speed of the substrate is beneficial for the saturated film growth and better film conformality. Increasing the carrier gas flow rate can effectively reduce the non-uniformity and non-conformality of the film, but the precursor utilization also decreases. Compared with the nonoptimal conditions, within a moderate range of carrier gas flow rate and substrate speed, the precursor utilization and film conformality have been improved. Focusing on the effect of the micro-scale features of the substrate, this study is a valuable step in extending spatial ALD for ultrathin films on miniature devices.

In-situ spatial and temporal electrical characterization of ZnO thin films deposited by atmospheric pressure chemical vapour deposition on flexible polymer substrates

A technique is presented for collecting data on both the spatial and temporal variations in the electrical properties of a film as it is deposited on a flexible substrate. A flexible printed circuit board substrate with parallel electrodes distributed across its surface was designed. Zinc oxide films were then deposited on the flexible substrate at different temperatures via atmospheric pressure chemical vapour deposition (AP-CVD) using a spatial atomic layer deposition system. AP-CVD is a promising high-throughput thin film deposition technique with applications in flexible electronics. Collecting data on the film properties in-situ allows us to directly observe how deposition conditions affect the evolution of those properties in real-time. The spatial uniformity of the growing film was monitored, and the various stages of film nucleation and growth on the polymer substrate were observed. The measured resistance of the films was observed to be very high until a critical amount of material has been deposited, consistent with Volmer–Weber growth. Furthermore, monitoring the film resistance during post-deposition cooling enabled immediate identification of metallic or semiconducting behaviour within the conductive ZnO films. This technique allows for a more complete understanding of metal chalcogen film growth and properties, and the high volume of data generated will be useful for future implementations of machine-learning directed materials science.

Effect of microgroove structures on the fluid dynamics and film conformality in spatial atomic layer deposition of Al2O3

With the development of semiconductors, efficient ultrathin coatings on large areas is of great significance to the commercial needs for the encapsulation of materials with micro- or nano-structures. Spatial Atomic Layer Deposition (ALD) is an emerging high throughput and economic technique which can deposit nano-scale films on substrates with different topographies. However, the complex fluid dynamics and diffusion kinetics in the spatial ALD system bring great challenge to the investigation and optimization of the film conformality. In this work, a two-dimensional model coupling Computational Fluid Dynamics (CFD) coupled with chemical kinetics details is built to investigate the hydrodynamics and film growth characteristics in spatial ALD system with different substrates. The effects of the microgroove structures and the microgroove heights on the velocity flow fields and the conformality of alumina films are studied, as shown in the Figure. With numerical simulations, our results show that higher aspect ratio of groove structure leads to more vortex flow at the corner of the microstructures. The motion of the substrates exacerbates the formation of vortex, which will definitely cause the precursor intermixing. Besides, the conformality of the alumina film decreases as the aspect ratio of microgroove structures increases. In order to ensure the self-limited ALD reaction and improve the film conformality, process parameters of total gap size, separate gas flow rate, the carrier gas flow rate as well as the motion velocity of the substrate are investigated. It is found that low carrier gas flow rate can not only reduce the chemical vapor deposition (CVD) growth, but also increase precursor utilization. This work is important for the packaging of micro structure devices and is rather instructive to the further design of spatial ALD system. Figure 1

In-situ observation of nucleation and property evolution in films grown with an atmospheric pressure spatial atomic layer deposition system

Atmospheric pressure—spatial atomic layer deposition (AP-SALD) is a promising open-air deposition technique for high-throughput manufacturing of nanoscale films, yet the nucleation and property evolution in these films has not been studied in detail. In this work, in situ reflectance spectroscopy was implemented in an AP-SALD system to measure the properties of Zinc oxide (ZnO) and Aluminum oxide (Al2O3) films during their deposition. For the first time, this revealed a substrate nucleation period for this technique, where the length of the nucleation time was sensitive to the deposition parameters. The in situ characterization of thickness showed that varying the deposition parameters can achieve a wide range of growth rates (0.1–3 nm/cycle), and the evolution of optical properties throughout film growth was observed. For ZnO, the initial bandgap increased when deposited at lower temperatures and subsequently decreased as the film thickness increased. Similarly, for Al2O3 the refractive index was lower for films deposited at a lower temperature and subsequently increased as the film thickness increased. Notably, where other implementations of reflectance spectroscopy require previous knowledge of the film’s optical properties to fit the spectra to optical dispersion models, the approach developed here utilizes a large range of initial guesses that are inputted into a Levenberg-Marquardt fitting algorithm in parallel to accurately determine both the film thickness and complex refractive index.

Atmospheric Plasma-Enhanced Spatial Chemical Vapor Deposition of SiO2 Using Trivinylmethoxysilane and Oxygen Plasma

SiO2 constitutes one of the most widely used dielectric materials in the microelectronics, packaging, and optical industries. Therefore, the development of new processes to deposit SiO2 at low temperature and in an affordable and scalable way are desirable. In this work, we present a low-temperature, open-air process based on spatial atomic layer deposition (SALD) that yields high purity SiO2 films at temperatures down to room temperature. The films were obtained by operating our SALD system in CVD mode (i.e., allowing precursor crosstalk), using an oxygen plasma in combination with trivinylmethoxysilane (TVMS). TVMS is an appealing precursor since it is highly volatile, is affordable, and does not contain halogen elements, thus being very suitable for application in atmospheric-pressure spatial deposition systems. Conversely, water, oxygen, hydrogen peroxide, or ozone did not show any reactivity with TVMS at temperatures up to 260 °C. Thus, when operating our system in ALD mode, no film could be obtained due to the lack of reactivity of the precursor with OH* surface groups. 3D printing was employed to fabricate custom heads integrating both the precursor injector and the atmospheric plasma generator. Our results show that conformal SiO2 thin films can be deposited by our atmospheric plasma-enhanced spatial chemical vapor deposition (APE-SCVD) approach at low temperatures (RT–180 °C) on different substrates, including silicon wafers, microglass slides, or even polymeric substrates with a high growth rate up to 2–5 nm/min. The deposition rate increased when increasing the power applied to the plasma reactor but decreased when increasing the deposition temperature due to the faster decay of the metastable oxygen radical species. FTIR results showed no differences for films deposited with different plasma powers. Conversely, temperature had an effect on the ratio between the AS1 and the AS2 bands. Even though the deposition of SiO2 was carried out at low temperatures in the open air using a metalorganic precursor, no contamination from SiNx or SiCx was observed by FTIR and XPS measurements. Our results open the door to the low-temperature, fast printing of Si-based devices.

Transient analysis and process optimization of the spatial atomic layer deposition using the dynamic mesh method

Spatial atomic layer deposition (ALD) is acknowledged as a high-throughput thin film preparation technique. Since the films are obtained at a high relative velocity of the substrate, the dynamic flow field distribution is more intricate compared to the traditional ALD. In this paper, by adopting the dynamic mesh method, a mathematical model combing fluid dynamics with chemical kinetics is established. Quantitative analysis is carried out to evaluate how different parameters influence precursor intermixing through this dynamic model. The viscous dragging effect caused by the relative movement of the substrate is also investigated. The good agreement between the mathematical results and the experimental data demonstrates the effectiveness of the dynamic model. To obtain a uniform thin film with a relatively high deposition rate and precursor usage, the motion speed of the substrate is also optimized. This numerical model has momentous guidance to the further process optimization and the spatial ALD system design.

Numerical study on the effectiveness of precursor isolation using N2 as gas barrier in spatial atomic layer deposition

Spatial atomic layer deposition (ALD) is capable to increase film deposition rate dramatically by eliminating the need of traditional pulse/purge steps in ALD process. Numerical simulations offer valuable information on spatial ALD system design and development. In this paper, a numerical study of inline spatial ALD process with a large gap (36 mm) is presented to investigate the effectiveness of precursor isolation using N2 flow as gas barrier in two different geometric designs, namely, top and bottom purge configurations. Bottom purge configuration is shown more effective in preventing precursor intermixing than top design. Higher N2 injecting flow rate and higher relative purging pressure are beneficial to construct an effective gas barrier in spatial ALD system. Evenly assigned precursor dosing pressure is advantageous to further prevent material intermixing. Transient material distributions in the flow field, contour plots of species, velocity field, and material tracelines have confirmed the effective gas barrier built by N2. Precursor intermixing molar fraction is shown as low as 0.0045%, and the intermixing molar concentration is as low as 9.105 × 10−5 mol/m3. The study provides invaluable information in determining geometric and process parameters for system design, and the effectiveness of precursor isolation using N2 as gas barrier in spatial ALD with a large gap is validated.

Performance Improvement of High Efficiency Mono-Crystalline Silicon Solar Cells by Modifying Rear-Side Morphology

In this work, aluminum oxide films with excellent passivation effects were prepared on the rear-side surface of passivated emitter and rear cells (PERCs) using a self-developed spatial atomic layer deposition system. Various rear-side surface morphologies were obtained through different etching treatments. We compared the PERCs with standard etching treatment and further polishing processes on rear-side surfaces. Experimental results show that compared with the unpolished cell, the polished cell attained superior electrical performance, particularly in open-circuit voltage (Voc) and short-circuit current density (Jsc), because of the more effective rear-side surface passivation and reabsorption of long-wavelength light. The improvement in Voc and Jsc raised the conversion efficiency to 19.27%. This study verifies that despite polished cells requiring complex processes, the polishing treatment displays application potential for achieving high efficiency in the solar industry.

Effect of scan speed on moisture barrier properties of aluminum oxide using spatial atomic layer deposition

Atomic layer deposition (ALD) has been shown to produce high-quality thin films with superior moisture barrier performance on polymer substrates. However, the conventional time-sequenced mode is incompatible with industrial needs due to its low deposition rate. One solution to overcome this throughput issue is to use spatial ALD. Recently, various approaches have been reported. The authors also developed a fast spatial ALD system using an industrial 2G (370 × 470 mm2) glass substrate. Using this system, the authors investigated the effect of a scan speed on the moisture barrier properties of aluminum oxide (Al2O3) thin films. While the scan speeds were varied over a wide range of 100–800 mm/s, the water vapor transmission rate increased only slightly, from 1.4 × 10−3 to 3.0 × 10−3 g/m2/day. At a scan speed of 800 mm/s, the deposition rate was 70 Å/min, which was about seven times higher than that of conventional ALD. Moreover, the physical and chemical properties of the thin films slightly worsened with the increase in the scan speed. Based on the above results, Al2O3 thin films prepared using the newly developed high-throughput and scalable spatial ALD system are a promising candidate for thin film encapsulation of large-scale flexible electronic applications.

Spatial atomic layer deposition of ZnO/TiO2 nanolaminates

Spatial atomic layer deposition (S-ALD) is a potential high-throughput manufacturing technique offering fast and large scale ultrathin films deposition. Here, an S-ALD system with modular injectors is introduced for fabricating binary oxides and their nanolaminates. By optimizing the deposition conditions, both ZnO and TiO2 films demonstrate linear growth and desired surface morphology. The as-deposited ZnO film has high carrier mobility, and the TiO2 film shows suitable optical transmittance and band gap. The ZnO/TiO2 nanolaminates are fabricated by alternating substrate movement between each S-ALD modular units of ZnO and TiO2. The grazing incidence x-ray diffraction spectra of nanolaminates demonstrating the signature peaks are weaker for the same thickness nanolaminates with more bilayers, suggesting tuning nanolaminates from crystalline to amorphous. Optical transmittances of ZnO/TiO2 laminates are enhanced with the increase of the bilayers' number in the visible range. Refractive indices of nanolaminates increase with the thickness of each bilayer decreasing, which demonstrates the feasibility of obtaining desired refractive indices by controlling the bilayer number. The electronic properties, including mobility, carrier concentration, and conductivity, are also tunable with different bilayers.

Effects of gap size, temperature and pumping pressure on the fluid dynamics and chemical kinetics of in-line spatial atomic layer deposition of Al2O3

Low throughput is a major limitation for industrial level atomic layer deposition (ALD) applications. Spatial ALD is regarded as a promising solution to this issue. With numerical simulations, this paper studies an in-line spatial ALD reactor by investigating the effects of gap size, temperature, and pumping pressure on the flow and surface chemical deposition processes in Al2O3 ALD. The precursor intermixing is a critical issue in spatial ALD system design, and it is highly dependent on the flow and material distributions. By numerical studies, it’s found that bigger gap, e.g., 2mm, results in less precursor intermixing, but generates slightly lower saturated deposition rate. Wafer temperature is shown as a significant factor in both flow and surface deposition processes. Higher temperature accelerates the diffusive mass transport, which largely contributes to the precursor intermixing. On the other hand, higher temperature increases film deposition rate. Well-maintained pumping pressure is beneficial to decrease the precursor intermixing level, while its effect on the chemical process is shown very weak. It is revealed that the time scale of in-line spatial ALD cycle is in tens of milliseconds, i.e., ∼15ms. Considering that the in-line spatial ALD is a continuous process without purging step, the ALD cycle time is greatly shortened, and the overall throughput is shown as high as ∼4nm/s, compared to several nm/min in traditional ALD.

Spatial atomic layer deposition on flexible porous substrates: ZnO on anodic aluminum oxide films and Al2O3 on Li ion battery electrodes

Spatial atomic layer deposition (S-ALD) was examined on flexible porous substrates utilizing a rotating cylinder reactor to perform the S-ALD. S-ALD was first explored on flexible polyethylene terephthalate polymer substrates to obtain S-ALD growth rates on flat surfaces. ZnO ALD with diethylzinc and ozone as the reactants at 50 °C was the model S-ALD system. ZnO S-ALD was then performed on nanoporous flexible anodic aluminum oxide (AAO) films. ZnO S-ALD in porous substrates depends on the pore diameter, pore aspect ratio, and reactant exposure time that define the gas transport. To evaluate these parameters, the Zn coverage profiles in the pores of the AAO films were measured using energy dispersive spectroscopy (EDS). EDS measurements were conducted for different reaction conditions and AAO pore geometries. Substrate speeds and reactant pulse durations were defined by rotating cylinder rates of 10, 100, and 200 revolutions per minute (RPM). AAO pore diameters of 10, 25, 50, and 100 nm were utilized with a pore length of 25 μm. Uniform Zn coverage profiles were obtained at 10 RPM and pore diameters of 100 nm. The Zn coverage was less uniform at higher RPM values and smaller pore diameters. These results indicate that S-ALD into porous substrates is feasible under certain reaction conditions. S-ALD was then performed on porous Li ion battery electrodes to test S-ALD on a technologically important porous substrate. Li0.20Mn0.54Ni0.13Co0.13O2 electrodes on flexible metal foil were coated with Al2O3 using 2–5 Al2O3 ALD cycles. The Al2O3 ALD was performed in the S-ALD reactor at a rotating cylinder rate of 10 RPM using trimethylaluminum and ozone as the reactants at 50 °C. The capacity of the electrodes was then tested versus number of charge–discharge cycles. These measurements revealed that the Al2O3 S-ALD coating on the electrodes enhanced the capacity stability. This S-ALD process could be extended to roll-to-roll operation for the commercialization of S-ALD for coating Li ion battery electrodes.

Mechanistic modeling study on process optimization and precursor utilization with atmospheric spatial atomic layer deposition

Spatial atomic layer deposition (SALD) is a promising technology with the aim of combining the advantages of excellent uniformity and conformity of temporal atomic layer deposition (ALD), and an industrial scalable and continuous process. In this manuscript, an experimental and numerical combined model of atmospheric SALD system is presented. To establish the connection between the process parameters and the growth efficiency, a quantitative model on reactant isolation, throughput, and precursor utilization is performed based on the separation gas flow rate, carrier gas flow rate, and precursor mass fraction. The simulation results based on this model show an inverse relation between the precursor usage and the carrier gas flow rate. With the constant carrier gas flow, the relationship of precursor usage and precursor mass fraction follows monotonic function. The precursor concentration, regardless of gas velocity, is the determinant factor of the minimal residual time. The narrow gap between precursor injecting heads and the substrate surface in general SALD system leads to a low Péclet number. In this situation, the gas diffusion act as a leading role in the precursor transport in the small gap rather than the convection. Fluid kinetics from the numerical model is independent of the specific structure, which is instructive for the SALD geometry design as well as its process optimization.

Investigation on the passivated Si/Al2O3 interface fabricated by non-vacuum spatial atomic layer deposition system.

Currently, aluminum oxide stacked with silicon nitride (Al2O3/SiNx:H) is a promising rear passivation material for high-efficiency P-type passivated emitter and rear cell (PERC). It has been indicated that atomic layer deposition system (ALD) is much more suitable to prepare high-quality Al2O3 films than plasma-enhanced chemical vapor deposition system and other process techniques. In this study, an ultrafast, non-vacuum spatial ALD with the deposition rate of around 10 nm/min, developed by our group, is hired to deposit Al2O3 films. Upon post-annealing for the Al2O3 films, the unwanted delamination, regarded as blisters, was found by an optical microscope. This may lead to a worse contact within the Si/Al2O3 interface, deteriorating the passivation quality. Thin stoichiometric silicon dioxide films prepared on the Si surface prior to Al2O3 fabrication effectively reduce a considerable amount of blisters. The residual blisters can be further out-gassed when the Al2O3 films are thinned to 8 nm and annealed above 650°C. Eventually, the entire PERC with the improved triple-layer SiO2/Al2O3/SiNx:H stacked passivation film has an obvious gain in open-circuit voltage (Voc) and short-circuit current (Jsc) because of the increased minority carrier lifetime and internal rear-side reflectance, respectively. The electrical performance of the optimized PERC with the Voc of 0.647 V, Jsc of 38.2 mA/cm2, fill factor of 0.776, and the efficiency of 19.18% can be achieved.

Design Considerations for ZnO Transistors Made Using Spatial ALD

We have used spatial atomic layer deposition (SALD) to fabricate a variety of thin film transistors using zinc oxide as the semiconductor and aluminum oxide as the insulator. The conductive electrodes are formed either from aluminum-doped zinc oxide, or from thermally evaporated metals. Spatial ALD can be performed at atmospheric pressure, and can grow coatings very quickly. Deposition occurs without a requirement for valve timing, by moving the substrate relative to the precursors flowing from a coating head. The proximity of the substrate to the coating head is controlled via a gas bearing design – allowing SALD to operate with purge times that are equivalent to the precursor exposure times (sub-second) unlike traditional chamber-based systems. In this talk we will discuss examples of thin film electronics with architectures that are enabled by ALD, with a particular focus on spatial ALD. We use the well known conformality of ALD to build self-aligned, sub-micron channel length, vertical transistors. The vertical transistor electrical performance is impressive compared to amorphous silicon TFTs, for example, yet the alignment tolerances inherent in the fabrication process are large.Our second approach to fabricating devices uses selective area deposition, with inkjet-printed inhibitor, to pattern all the active layers. We build full transistors and circuits using one inhibitor ink, the SALD system, and an oxygen plasma to clean the substrate. Performance of the resulting transistors and circuits match photolithographically patterned ones.