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

Fouling in membrane bioreactors used in wastewater treatment

International Technology Roadmap for Semiconductors 2003の要求清浄度について － シリコンウエハ表面と雰囲気環境に要求される清浄度, 分析方法の現状について －

https://cyberleninka.org/article/n/247805.pdf

A brief review of atomic layer deposition: from fundamentals to applications

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

HfO2 thin films were deposited on Si wafers using an atomic layer deposition technique at temperatures ranging from 200 to 400 °C with HfCl4 as the precursor and H2O as the oxidant. The time-dependent interfacial-layer growth behavior was dependent on the deposition temperature. The interfacial layer grew with increasing deposition time at 200 °C. However, the film thicknesses decreased with increasing deposition time after reaching a certain maximum value at 300 and 400 °C due to the enhanced dissolution of SiOx into the growing films at these temperatures. Post-annealing at 800 °C under a N2 atmosphere resulted in the precipitation of a Si-rich interfacial layer even for the initially interfacial layer free films. This had the effect of reducing the capacitance density of the films.

Chemical interaction between atomic-layer-deposited HfO2 thin films and the Si substrate

The chemical states of the HfO2/Si (100) interface were investigated using transmission electron microscopy and high-resolution x-ray photoelectron spectroscopy. The depth distributions of Hf chemical states showed that the Hf 4f binding energy remains unchanged with the depth and there is no signature of more than one Hf-O state. These facts strongly suggest that the chemical state of the interfacial layer is not Hf-silicate, as previously believed. Instead, the compositions are mainly Si2O3 and SiO2, judging from the deconvolution of Si 2p spectra. The dielectric constant κ=4.8 of the interfacial layer is also consistent with the above conclusions.

Chemical structure of the interface in ultrathin HfO2/Si films

Potential and limitations of alum or zeolite addition to improve the performance of a submerged membrane bioreactor.

Interfacial reactions between HfO2 thin films and a Si substrate during thin-film growth and postannealing under a N2 atmosphere were investigated by high-resolution transmission electron microscopy, Auger electron spectroscopy, and electrical measurements of metal–insulator–semiconductor capacitors. HfO2 thin films were deposited on HF-cleaned Si wafers by a chemical-vapor-deposition technique at a wafer temperature of 200 °C using a carbon-free precursor [Hf(NO3)4]. The film thicknesses ranged from 1.5 to 5.6 nm. During the initial stage of film growth, the Si surface oxidized to form a Si-rich hafnium silicate film. With increasing deposition time, Hf-rich hafnium silicate films grew. Postannealing resulted in a double-layered film structure with upper and interfacial layers having dielectric constants of approximately 9.3 and 5.6, respectively. The results were compared with the results from HfO2 films grown on SiO2-passivated Si wafers.

Interfacial reaction between chemically vapor-deposited HfO2 thin films and a HF-cleaned Si substrate during film growth and postannealing

HfO2 gate dielectric thin-films were deposited on Si wafers using an atomic-layer deposition (ALD) technique with HfCl4 and either H2O or O3 as the precursor and oxidant, respectively. Although the ALD reactions using either H2O or O3 were successfully confirmed at a deposition temperature of 300 °C, the structural and electrical properties of the HfO2 films grown using the two oxidants were quite different. The stronger oxidation power of the O3 compared to H2O increased the oxygen concentration in the HfO2 film and the rate of interfacial SiO2 formation even at the as-deposited state. Because of the larger oxygen concentration, the decrease in the capacitance density of the film grown with O3 after rapid thermal annealing at 750 °C under N2 atmosphere was slightly larger than that of the HfO2 film grown with H2O. Apart from this weakness, all the other electrical properties, including the fixed charge density, the interface trap density, the leakage current density and the hysteresis in the capacitance–...

Moonju Cho

Papers

Chemical interaction between atomic-layer-deposited HfO2 thin films and the Si substrate

Chemical structure of the interface in ultrathin HfO2/Si films

Potential and limitations of alum or zeolite addition to improve the performance of a submerged membrane bioreactor.

Interfacial reaction between chemically vapor-deposited HfO2 thin films and a HF-cleaned Si substrate during film growth and postannealing

Comparison of HfO2 films grown by atomic layer deposition using HfCl4 and H2O or O3 as the oxidant