Atomic layer deposition: an overview.

The surface and materials science of tin oxide

Atomic layer deposition(ALD), a chemical vapor deposition technique based on sequential self-terminating gas–solid reactions, has for about four decades been applied for manufacturing conformal inorganic material layers with thickness down to the nanometer range. Despite the numerous successful applications of material growth by ALD, many physicochemical processes that control ALD growth are not yet sufficiently understood. To increase understanding of ALD processes, overviews are needed not only of the existing ALD processes and their applications, but also of the knowledge of the surface chemistry of specific ALD processes. This work aims to start the overviews on specific ALD processes by reviewing the experimental information available on the surface chemistry of the trimethylaluminum/water process. This process is generally known as a rather ideal ALD process, and plenty of information is available on its surface chemistry. This in-depth summary of the surface chemistry of one representative ALD process aims also to provide a view on the current status of understanding the surface chemistry of ALD, in general. The review starts by describing the basic characteristics of ALD, discussing the history of ALD—including the question who made the first ALD experiments—and giving an overview of the two-reactant ALD processes investigated to date. Second, the basic concepts related to the surface chemistry of ALD are described from a generic viewpoint applicable to all ALD processes based on compound reactants. This description includes physicochemical requirements for self-terminating reactions,reaction kinetics, typical chemisorption mechanisms, factors causing saturation, reasons for growth of less than a monolayer per cycle, effect of the temperature and number of cycles on the growth per cycle (GPC), and the growth mode. A comparison is made of three models available for estimating the sterically allowed value of GPC in ALD. Third, the experimental information on the surface chemistry in the trimethylaluminum/water ALD process are reviewed using the concepts developed in the second part of this review. The results are reviewed critically, with an aim to combine the information obtained in different types of investigations, such as growth experiments on flat substrates and reaction chemistry investigation on high-surface-area materials. Although the surface chemistry of the trimethylaluminum/water ALD process is rather well understood, systematic investigations of the reaction kinetics and the growth mode on different substrates are still missing. The last part of the review is devoted to discussing issues which may hamper surface chemistry investigations of ALD, such as problematic historical assumptions, nonstandard terminology, and the effect of experimental conditions on the surface chemistry of ALD. I hope that this review can help the newcomer get acquainted with the exciting and challenging field of surface chemistry of ALD and can serve as a useful guide for the specialist towards the fifth decade of ALD research.

Surface chemistry of atomic layer deposition: A case study for the trimethylaluminum/water process

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

Synthesis of nanocrystals with exposed high-energy facets is a well-known challenge in many fields of science and technology. The higher reactivity of these facets simultaneously makes them desirable catalysts for sluggish chemical reactions and leads to their small populations in an equilibrated crystal. Using anatase TiO2 as an example, we demonstrate a facile approach for creating high-surface-area stable nanosheets comprising nearly 100% exposed (001) facets. Our approach relies on spontaneous assembly of the nanosheets into three-dimensional hierarchical spheres, which stabilizes them from collapse. We show that the high surface density of exposed TiO2 (001) facets leads to fast lithium insertion/deinsertion processes in batteries that mimic features seen in high-power electrochemical capacitors.

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Constructing Hierarchical Spheres from Large Ultrathin Anatase TiO2 Nanosheets with Nearly 100% Exposed (001) Facets for Fast Reversible Lithium Storage

A nanostructured three-dimensional (3D) microbattery has been produced and cycled in a Li-ion battery. It consists of a current collector of aluminum nanorods, a uniform layer of 17 nm TiO2 covering the nanorods made using ALD, an electrolyte and metallic lithium counter electrode. The battery is electrochemically cycled more than 50 times. The increase in total capacity is 10 times when using a 3D architechture compared to a 2D system for the same footprint area.

Self-supported three-dimensional nanoelectrodes for microbattery applications.

Polycrystalline monoclinic HfO2 films were atomic layer deposited on Si(100) substrates by a nonhydrous carbon-free process of HfI4 and O2. The oxygen to hafnium ratio corresponded to the stoichiometric dioxide within the limits of accuracy of ion beam analysis. A 1.5–2.0 nm thick SiO2 interface layer formed between the HfO2 films and Si substrates. Hysteresis of the capacitance–voltage curves was observed in Al/HfO2/p-Si(100) structures with oxide grown in the substrate temperature range of 570–755 °C. The hysteresis ceased with an increase in O2 pressure. The effective permittivity of the dielectric layers varied between 12 and 16. The breakdown voltages were found to be lower in the case of higher oxygen doses and higher HfO2 deposition temperatures.

Properties of hafnium oxide films grown by atomic layer deposition from hafnium tetraiodide and oxygen

Atomic layer growth of epitaxial TiO2 thin films from TiCl4 and H2O on α-Al2O3 substrates

TiO2 thin films have been grown on amorphous soda lime glass and polycrystalline silicon substrates from TiI4 and H2O2 by atomic layer deposition (ALD) in the temperature range 250–490 °C The film growth rate and refractive index increased linearly with growth temperature up to 300 °C Between 300 °C and 400 °C, the film growth rate tended to stabilize Above 400 °C, there was a further rapid increase in the growth rate, together with a corresponding increase in the thickness profile The refractive index reached 270–275 in the films grown above 300 °C The films contained low amounts of residual hydrogen and were virtually iodine-free When deposited below 300 °C and above 325 °C, the films contained weakly crystallized, but still distinct, anatase and rutile phases, respectively Reflective high-energy electron diffraction (RHEED) studies revealed that the uppermost layers of the films grown on silicon at 275 °C, 325 °C, and 425 °C contained anatase phase, regardless of deposition temperature In the temperature range 300–325 °C, a transition region was established where either the films became less ordered, or they contained rather strongly ordered, but unstable, suboxide phases The suboxide phase, when present, was transformed into a mixture of anatase and rutile when stored in air at room temperature

Anders Hårsta

Papers

Self-supported three-dimensional nanoelectrodes for microbattery applications.

Properties of hafnium oxide films grown by atomic layer deposition from hafnium tetraiodide and oxygen

Atomic layer growth of epitaxial TiO2 thin films from TiCl4 and H2O on α-Al2O3 substrates

Atomic Layer Deposition of Titanium Oxide from TiI4 and H2O2

Atomic layer deposition of zirconium oxide from zirconium tetraiodide, water and hydrogen peroxide