Atomic layer deposition: an overview.

Metal Oxides and Oxysalts as Anode Materials for Li Ion Batteries

An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

Semiconductor device, and manufacturing method thereof

Atomic layer deposition (ALD) is gaining attention as a thin film deposition method, uniquely suitable for depositing uniform and conformal films on complex three-dimensional topographies. The deposition of a film of a given material by ALD relies on the successive, separated, and self-terminating gas–solid reactions of typically two gaseous reactants. Hundreds of ALD chemistries have been found for depositing a variety of materials during the past decades, mostly for inorganic materials but lately also for organic and inorganic–organic hybrid compounds. One factor that often dictates the properties of ALD films in actual applications is the crystallinity of the grown film: Is the material amorphous or, if it is crystalline, which phase(s) is (are) present. In this thematic review, we first describe the basics of ALD, summarize the two-reactant ALD processes to grow inorganic materials developed to-date, updating the information of an earlier review on ALD [R. L. Puurunen, J. Appl. Phys. 97, 121301 (2005)], and give an overview of the status of processing ternary compounds by ALD. We then proceed to analyze the published experimental data for information on the crystallinity and phase of inorganic materials deposited by ALD from different reactants at different temperatures. The data are collected for films in their as-deposited state and tabulated for easy reference. Case studies are presented to illustrate the effect of different process parameters on crystallinity for representative materials: aluminium oxide, zirconium oxide, zinc oxide, titanium nitride, zinc zulfide, and ruthenium. Finally, we discuss the general trends in the development of film crystallinity as function of ALD process parameters. The authors hope that this review will help newcomers to ALD to familiarize themselves with the complex world of crystalline ALD films and, at the same time, serve for the expert as a handbook-type reference source on ALD processes and film crystallinity.

Crystallinity of inorganic films grown by atomic layer deposition: Overview and general trends

Platinum-nanoparticle-based catalysts are widely used in many important chemical processes and automobile industries. Downsizing catalyst nanoparticles to single atoms is highly desirable to maximize their use efficiency, however, very challenging. Here we report a practical synthesis for isolated single Pt atoms anchored to graphene nanosheet using the atomic layer deposition (ALD) technique. ALD offers the capability of precise control of catalyst size span from single atom, subnanometer cluster to nanoparticle. The single-atom catalysts exhibit significantly improved catalytic activity (up to 10 times) over that of the state-of-the-art commercial Pt/C catalyst. X-ray absorption fine structure (XAFS) analyses reveal that the low-coordination and partially unoccupied densities of states of 5d orbital of Pt atoms are responsible for the excellent performance. This work is anticipated to form the basis for the exploration of a next generation of highly efficient single-atom catalysts for various applications.

/pdf/single-atom-catalysis-using-pt-graphene-achieved-through-xvargymz49.pdf

Single-atom Catalysis Using Pt/Graphene Achieved through Atomic Layer Deposition

In this paper recent work on the application of in situ spectroscopic ellipsometry (SE) during thin film synthesis by atomic layer deposition (ALD) is reviewed. In particular, the versatility of this all-optical diagnostic is demonstrated by results obtained on Al2O3, HfO2, Er2O3, TiO2, Ta2O5, TiN and TaNx films with thicknesses ranging from 0.1 to 100 nm. By acquiring SE data in between the ALD cycles and by analysing the film thickness and the energy dispersion of the optical constants of the films, the layer-by-layer growth and material properties of the films can be studied in detail. The growth rate per cycle and the ALD saturation curves can be determined directly by monitoring the film thickness as a function of the number of cycles, while also the nucleation behaviour of the films on various substrates and submonolayer surface changes during the ALD half-cycles can be probed. The energy dispersion relation provides information on the optical properties, the crystalline phase and the material composition of the films. For metallic films, electrical properties can be calculated from the Drude absorption yielding insight into the electrical resistivity and electron scattering effects in ultrathin films.

https://iopscience.iop.org/article/10.1088/0022-3727/42/7/073001/pdf

In situ spectroscopic ellipsometry as a versatile tool for studying atomic layer deposition

In this note it is demonstrated that optical emission spectroscopy (OES) is an easy-to-implement and valuable tool to study, optimize, and monitor thin film growth by plasma-assisted atomic layer deposition (ALD). The species in the plasma can be identified through the analysis of the light emitted by the plasma. OES provides therefore information on the reactant species delivered to the surface by the plasma but it also yields unique insight into the surface reaction products and, as a consequence, on the reaction mechanisms of the deposition process. Time-resolved measurements reveal information about the amount of precursor dosing and length of plasma exposure needed to saturate the self-limiting half reactions, which is useful for the optimization of the ALD process. Furthermore, time-resolved OES can also be used as an easy-to-implement process monitoring tool for plasma-assisted ALD processes on production equipment; for example, to monitor reactor wall conditions or to detect process faults in real time.

/pdf/optical-emission-spectroscopy-as-a-tool-for-studying-56jkgbvyx4.pdf

Optical emission spectroscopy as a tool for studying, optimizing, and monitoring plasma-assisted atomic layer deposition processes

For plasma-assisted atomic layer deposition (ALD), reaching conformal deposition in high aspect ratio structures is less straightforward than for thermal ALD due to surface recombination loss of plasma radicals. To obtain a detailed insight into the consequences of this additional radical loss, the physical processes in plasma-assisted ALD affecting conformality were identified and investigated through Monte Carlo simulations. The conformality was dictated by the recombination probability r, the reaction probability s, and the diffusion rate of particles. When recombination losses play a role, the saturation dose depended strongly on the value of r. For the deposition profiles, a minimum at the bottom of trench structures was observed (before reaching saturation), which was more pronounced with larger values of r. In turn, three deposition regimes could be identified, i.e., a reaction-limited regime, a diffusion-limited regime, and a new regime that is recombination-limited. For low values of r, conformal deposition in high aspect ratio structures can still be achieved, as observed for several metal oxides, even for aspect ratios as large as 30. For high surface recombination loss probabilities, as appears to be the case for many metals, achieving a reasonable conformality becomes challenging, especially for aspect ratios >10.

/pdf/conformality-of-plasma-assisted-ald-physical-processes-and-4uaei40ou9.pdf

Conformality of Plasma-Assisted ALD: Physical Processes and Modeling

Nanostructuring is targeted as a solution to achieve the improvements required for implementing Li-ion batteries in a wide range of applications. These applications range in size from electrical vehicles down to microsystems. Atomic layer deposition (ALD) could be an enabling technology for nanostructured Li-ion batteries as it is capable of depositing ultrathin films (1–100 nm) in complex structures with precise growth control. The potential of ALD is reviewed for three battery concepts that can be distinguished, i.e., particle-based electrodes, 3D-structured electrodes, and 3D all-solid-state microbatteries. It is discussed that a large range of materials can be deposited by ALD and recent demonstrations of battery improvements by ALD are used to exemplify its large potential.

/pdf/atomic-layer-deposition-for-nanostructured-li-ion-batteries-2xu6jfwkb8.pdf

Atomic layer deposition for nanostructured Li-ion batteries

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.

/pdf/atomic-layer-etching-what-can-we-learn-from-atomic-layer-1kdyg3ejub.pdf

Hcm Harm Knoops

Papers

In situ spectroscopic ellipsometry as a versatile tool for studying atomic layer deposition

Optical emission spectroscopy as a tool for studying, optimizing, and monitoring plasma-assisted atomic layer deposition processes

Conformality of Plasma-Assisted ALD: Physical Processes and Modeling

Atomic layer deposition for nanostructured Li-ion batteries

Atomic Layer Etching: What Can We Learn from Atomic Layer Deposition?