Atomic layer deposition (ALD) is a technique capable of producing ultrathin conformal films with atomic level control over thickness. A major drawback of ALD is its low deposition rate, making ALD less attractive for applications that require high throughput processing. An approach to overcome this drawback is spatial ALD, i.e., an ALD mode where the half-reactions are separated spatially instead of through the use of purge steps. This allows for high deposition rate and high throughput ALD without compromising the typical ALD assets. This paper gives a perspective of past and current developments in spatial ALD. The technology is discussed and the main players are identified. Furthermore, this overview highlights current as well as new applications for spatial ALD, with a focus on photovoltaics and flexible electronics.
Al2O3 thin films deposited at rates as high as 1.2 nm s−1 using spatially separated atomic layer deposition show excellent solar cell surface passivation properties, i.e., recombination velocities of <2 cm s−1. This disruptive ALD concept opens the way for cost‐effective manufacturing with high industrial throughput numbers.
Zinc oxide thin films have been deposited at high growth rates (up to ~1 nm/s) by spatial atomic layer deposition technique at atmospheric pressure. Water has been used as oxidant for diethylzinc (DEZ) at deposition temperatures between 75 and 250 °C. The electrical, structural (crystallinity and morphology), and optical properties of the films have been analyzed by using Hall, four-point probe, X-ray diffraction, scanning electron microscopy, spectrophotometry, and photoluminescence, respectively. All the films have c-axis (100) preferential orientation, good crystalline quality and high transparency (∼ 85%) in the visible range. By varying the DEZ partial pressure, the electrical properties of ZnO can be controlled, ranging from heavily n-type conductive (with 4 mOhm.cm resistivity for 250 nm thickness) to insulating. Combining the high deposition rates with a precise control of functional properties (i.e., conductivity and transparency) of the films, the industrially scalable spatial ALD technique can become a disruptive manufacturing method for the ZnO-based industry.
Atmospheric pressure spatial atomic layer deposition (AP-SALD) has recently emerged as an appealing technique for rapidly producing high quality oxides. Here, we focus on the use of AP-SALD to deposit functional ZnO thin films, particularly on the reactors used, the film properties, and the dopants that have been studied. We highlight how these films are advantageous for the performance of solar cells, organometal halide perovskite light emitting diodes, and thin-film transistors. Future AP-SALD technology will enable the commercial processing of thin films over large areas on a sheet-to-sheet and roll-to-roll basis, with new reactor designs emerging for flexible plastic and paper electronics.
Spatial atomic layer deposition can be used as a high-throughput manufacturing technique in functional thin film deposition for applications such as flexible electronics. This; however, requires low-temperature processing and handling of flexible substrates. The authors investigate the process conditions under which low-temperature spatial atomic layer deposition of alumina from trimethyl aluminum and water is possible. The water partial pressure is the critical parameter in this case. Finally, our approach to roll-to-roll spatial atomic layer deposition is discussed.
Atomic layer deposition (ALD) is renowned for its step coverage in porous substrates. Several emerging applications require a combination of this high step coverage with high throughput ALD, like spatial ALD. Often, high throughput ALD is performed at atmospheric pressure, and therefore, the effect of reactor pressure on the saturation dose is investigated. ALD inside porous substrates is governed by three key parameters: the reaction probability, the pore aspect ratio, and the precursor diffusion coefficient, of which the latter one contains the reactor pressure dependency. The effect of these parameters on the saturation dose is validated using Monte Carlo modeling, where the reactor pressure dependency is included through the mean free path. A reaction-limited and a diffusion-limited regime can be identified, and it is shown that for many realistic experimental conditions, even at low reactor pressures, the saturation dose is in the diffusion-limited regime. An expression for the pressure dependent saturation dose in the diffusion-limited regime is derived. For small pore diameters, the saturation dose is pressure independent, but for larger pores, higher saturation doses are required for atmospheric reactor pressures than for low reactor pressures. However, as high reactor pressures enable much higher precursor partial pressures than low reactor pressures, the resulting saturation times can be much shorter at atmospheric pressure than low pressure. Often, high surface area porous substrates will lead to supply limited conditions, and increased saturation times have to be taken into account. These results show that the atmospheric pressure ALD can be used for high throughput ALD inside porous substrates, as long as high precursor partial pressures and molar flows can be applied. This is experimentally demonstrated by a near 100% step coverage obtained by atmospheric spatial ALD of alumina in high aspect ratio pores.
Document VersionPublisher's PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. This article explores the history of atomic layer deposition (ALD) and its relationship with the American Vacuum Society (AVS). The authors describe the origin and history of ALD science in the 1960s and 1970s. They also report on how the science and technology of ALD progressed through the 1990s and 2000s and continues today. This article focuses on how ALD developed within the AVS and continues to evolve through interactions made possible by the AVS, in particular, the annual International AVS ALD Conference. This conference benefits students, academics, researchers, and industry practitioners alike who seek to understand the fundamentals of self-limiting, alternating binary surface reactions, and how they can be applied to form functional (and sometimes profitable) thin film materials. The flexible structure of the AVS allowed the AVS to quickly organize the ALD community and create a primary conference home. Many new research areas have grown out of the original concepts of "Atomic Layer Epitaxy" and "Molecular Layering," and some of them are described in this article. The people and research in the ALD field continue to evolve, and the AVS ALD Conference is a primary example of how the AVS can help a field expand and flourish.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.