Plasma-Enhanced Atomic Layer Deposition of Al<inf>2</inf>O<inf>3</inf> on Graphene Using Monolayer hBN as Interfacial Layer

Abstract: The deposition of dielectric materials on graphene is one of the bottlenecks for unlocking the potential of graphene in electronic applications. The plasma enhanced atomic layer deposition of 10 nm thin high quality aluminum oxide (Al2O3) on graphene is demonstrated using a monolayer of hexagonal boron nitride (hBN) as protection layer. Raman spectroscopy is performed to analyze possible structural changes of the graphene lattice caused by the plasma deposition. The results show that a monolayer of hBN in combination with an optimized deposition process can effectively protect graphene from damage, while significant damage is observed without an hBN layer. Electrical characterization of double gated graphene field effect devices confirms that the graphene does not degrade during the plasma deposition of Al2O3. The leakage current densities are consistently below 1 pA µm−2 for electric fields across the insulators of up to 8 MV cm−1, with irreversible breakdown happening above. Such breakdown electric fields are typical for Al2O3 and can be seen as an indicator for high quality dielectric films

ALD, ALE and 2D Materials:atomic scale processing for optoelectronics applications

\u3cp\u3eMany applications are seeing a trend towards miniaturization and utilization of nanoscale effects. In this presentation atomic-scale processing techniques offered by Oxford Instruments will be discussed and possible benefits for optoelectronics applications are highlighted.\u3c/p\u3

Atomic layer deposition : from reaction mechanisms to 3D-integrated micro-batteries

One major difficulty in maintaining the size reduction in electronic devices is the controlled deposition of high-quality thin films with the right film properties. Besides this trend of miniaturization in information processing technology, i.e., the "More-Moore" trend, there has been another trend for non-digital technology which is designated as "More-than-Moore". "More-than-Moore" is the trend towards diversification within electronic devices, in which multiple functionalities are integrated into a single unit of the device. All-solid-state 3D-integrated micro-batteries are a good example of the More-than-Moore approach as they integrate energy storage, which is a traditionally macroscopic non-semiconductor technology, into a chip-size unit using techniques compatible with semiconductor technology. In all-solid-state 3D-integrated microbatteries, the various battery materials have to be deposited as thin films. Furthermore, to achieve a high capacity per footprint area on the chip surface, the thin films have to be deposited in high-aspect-ratio structures etched in the Si substrate. Controlled deposition of high-quality films with the right film properties is therefore also a challenge in this research field. A thin-film deposition technique which typically exhibits a high material quality, a high uniformity, precise growth control, and an excellent conformality is atomic layer deposition (ALD). ALD has the potential to be an enabling technology for a wide range of applications. To be able to develop new ALD processes and materials, detailed understanding of the reaction mechanisms and the ALD process itself are essential. Besides the conventional thermallydriven ALD processes, the usage of energy-enhanced methods is considered, i.e., plasma-assisted and ozone-based processes. Plasma-assisted ALD can for instance facilitate deposition of conductive films. Furthermore, oxygen plasma and ozone gas are well-suited to grow oxide thin films even at low substrate temperatures. The reactive reactants used can, however, recombine at surfaces which could complicate deposition in 3D structures. In this thesis new energy-enhanced ALD processes are developed and further understanding is obtaned on their reaction mechanisms. Also the ability of energy-enhanced ALD processes to conformally coat 3D structures is investigated. Moreover, the application of ALD in energy technologies is further explored by focussing on solid-state 3D-integrated batteries. The use of ALD in Li-ion battery synthesis is relatively unexplored and therefore the potential of ALD for Li-ion batteries is reviewed in this work. Not only the More-than-Moore application of all-solid-state 3D-integrated microbatteries is considered, but also larger-scale Li-ion battery concepts that can benefit from ALD as well. Nanostructuring is targeted as a solution to achieve the improvements required for implementing batteries in a wide range of applications. The potential of ALD is discussed for three battery concepts that can be distinguished, i.e., particle-based electrodes, 3D-structured electrodes, and 3D solid-state micro-batteries. It is discussed that a large range of materials can be deposited by ALD and recent demonstrations of improvements in battery technology by ALD are used to exemplify its large potential. Conformal deposition of conductive materials is needed in a variety of More-than-Moore applications, e.g., for electrodes and current collectors. TiN and TaN deposited by plasma-assisted ALD were demonstrated to serve as Li barrier and anode current collector for micro-batteries and also as Cu diffusion barrier in advanced interconnect technology for 3D-integration. Furthermore, conformal deposition of TiN films by plasma-assisted ALD was demonstrated. For some electrodes, such as the cathode current collector, a highly-chemically-stable conductive material is needed. A plasma-assisted ALD process was developed for the deposition of Pt films with excellent material properties in terms of density and resistivity. By using an additional H2-gas reduction-step, the deposition of Pt at low temperatures with good material properties was achieved, which can be of interest for deposition of Pt on plastics. Furthermore, using longer plasma exposure times, PtO2 could be deposited which is difficult to obtain by ALD. Using mass spectrometry, the reaction mechanism of plasma-assisted ALD of TaNx was investigated. For this process the reaction products released from the surface during the plasma step were found to interact with the plasma. Furthermore, the material properties of TaNx are influenced to a large extent by this interaction. Interaction of ALD reaction products with the plasma is expected to be of general significance for plasma-assisted ALD processes. The reaction products of the thermal ALD process for Pt were quantified using insitu gas-phase infrared spectroscopy and a reaction mechanism was proposed. The film growth was found to be ruled by the surface coverage of dissociatively chemisorbed oxygen with which the precursor molecules interact. The capability of plasma-assisted ALD to deposit in 3D structures was investigated using Monte Carlo simulations. It was found that deposition in 3D structures can be classified in three regimes: i.e., reaction-limited, diffusionlimited, and recombination-limited. For low values of the recombination probability, or, conformal deposition in high-aspect-ratio structures can still be achieved, as also experimentally observed for several metal oxides. For high values of the recombination probability, r, as appears to be the case for many metals, achieving a reasonable conformality becomes challenging, especially for aspect ratios >10. Sufficient conformal deposition was demonstrated for both the TiN and the Pt plasma-assisted ALD processes. For the medium aspect ratios targeted for the Li-ion micro-batteries, plasma-assisted ALD should be able to conformally deposit all materials. Similarly the loss of O3 in 3D structures was investigated where the loss of O3 on several materials was tested. To determine O3 recombination probabilities over a wide range, a method was developed using high-aspect-ratio capillaries at the inlet to a mass spectrometer. O3 typically has higher loss on materials such as MnOx and Co3O4, which can also be considered as battery materials. Several material systems were investigated and a considerable amount of fundamental understanding in ALD was generated. In particular, understanding of energy-enhanced ALD processes and understanding of their ability to coat 3D structures conformally are essential for many new application fields in which these techniques will be required

Ion energy control during plasma-enhanced atomic layer deposition: enabling materials control and selective processing in the third dimension

As we enter an era of atomic scale devices, there is a strict need for precise control over the thickness and properties of materials em-ployed in device fabrication [1,2]. Furthermore, next-generation de-vices consist of various material layers across both planar and three-dimensional (3D) layouts which has led to an additional need for processing materials in a selective manner [3,4]. Plasma-enhanced atomic layer deposition (ALD) is a technique that uses the species generated in a plasma (i.e. radicals, ions) for processing materials at the atomic level. In this article, we demonstrate how implementing ion energy control in plasma ALD enhances the versatility of this atomic scale processing technique by enabling control over a wide range of material properties during deposition. Furthermore, we show how controlling ion energies during plasma ALD on 3D trench-shaped nanostructures provide a novel approach for topographically selective materials processing

Plasma atomic layer deposition

Plasma atomic layer deposition (ALD) is optimized through modulation of the gas residence time during an excited species phase, wherein activated reactant is supplied such as from a plasma. Reduced residence time increases the quality of the deposited layer, such as reducing wet etch rates, increasing index of refraction and/or reducing impurities in the layer. For example, dielectric layers, particularly silicon nitride films, formed from such optimized plasma ALD processes have low levels of impurities remaining from the silicon precursor

Plasma atomic layer deposition

Plasma atomic layer deposition (ALD) is optimized through modulation of the gas residence time during an excited species phase, wherein activated reactant is supplied such as from a plasma. Reduced residence time increases the quality of the deposited layer, such as reducing wet etch rates, increasing index of refraction and/or reducing impurities in the layer. For example, dielectric layers, particularly silicon nitride films, formed from such optimized plasma ALD processes have low levels of impurities remaining from the silicon precursor

Atomic layer etching : what can we learn from atomic layer deposition?

Current trends in semiconductor device manufacturing impose extremely stringent requirements on nanoscale processing techniques, both in terms of accurately controlling material properties and in terms of precisely controlling nanometer dimensions. To take nanostructuring by dry etching to the next level, there is a fast growing interest in so-called atomic layer etching processes, which are considered the etching counterpart of atomic layer deposition processes. In this article, past research efforts are reviewed and the key defining characteristics of atomic layer etching are identified, such as cyclic step-wise processing, self-limiting surface chemistry, and repeated removal of atomic layers (not necessarily a full monolayer) of the material. Subsequently, further parallels are drawn with the more mature and mainstream technology of atomic layer deposition from which lessons and concepts are extracted that can be beneficial for advancing the field of atomic layer etching

Atomic layer deposition of silicon nitride from bis(tertiary-butyl-amino)silane and N2 plasma studied by in situ gas phase and surface infrared spectroscopy

The atomic layer deposition process (ALD) of silicon nitride (SiNx), employing bis(tertiary-butyl-amino)silane (SiH2(NHtBu)2, BTBAS) and N2 plasma, was investigated by means of Fourier transform infrared (FT-IR) spectroscopy. In situ gas phase, film, and surface infrared measurements have been performed during different stages of the ALD process. From gas phase IR measurements it can be concluded that tert-butylamine is the main reaction product released during precursor exposure. Infrared measurements performed on the deposited SiNx films revealed the incorporation of C in the form of CN and SiC, where more C is incorporated at a deposition temperature of 85 °C compared to 155 or 275 °C. Surface IR measurements, employing a four-axes sample manipulator, showed the formation of SiH- and NH-groups on the surface and revealed that most of the H is incorporated during the precursor exposure step. Furthermore, after the N2 plasma step a vibrational mode around 2090 cm–1 was observed. This mode could be attributed to the formation of Si-NCH complexes and are likely to be formed by the so-called redeposition effect. For higher deposition temperatures, these Si-NCH complexes are removed again during the following precursor exposure step. At 85 °C, some of the complexes remain at the surface. Overall, from the gained knowledge about the surface chemistry, a reaction mechanism of the SiNx ALD process has been proposed

Status and prospects of plasma-assisted atomic layer deposition

Processing at the atomic scale is becoming increasingly critical for state-of-the-art electronic devices for computing and data storage, but also for emerging technologies such as related to the internet-of-things, artificial intelligence, and quantum computing. To this end, strong interest in improving nanoscale fabrication techniques such as atomic layer deposition (ALD) has been present. New ALD processes are being sought continuously and particularly plasma-assisted processes are considered an enabler for a wide range of applications because of their enhanced reactivity. This review provides an update on the status and prospects of plasma-assisted ALD with a focus on the developments since the publication of the review by Profijt et al. [J. Vac. Sci. Technol. A 29, 050801 (2011)]. In the past few years, plasma ALD has obtained a prominent position in the field of ALD with (i) a strong application base as demonstrated by the breakthrough in high-volume manufacturing; (ii) a large number of established processes, out of which several are being enabled by the plasma step; and (iii) a wide range of plasma ALD reactor designs, demonstrating many methods by which plasma species can be applied in ALD processes. In addition, new fundamental insights have been obtained, for instance, with respect to plasma damage, on the effect of ions on the material properties and on the so-called redeposition effect. Regarding new and emerging developments, plasma ALD is expected to take a prominent position in the atomic-scale processing toolbox and will contribute to ongoing developments in area-selective deposition, controlled growth of 2D materials, and atomic layer etching.\u3cbr/\u3