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

Electronics obtained through the bottom-up approach of molecular-level control of material composition and structure may lead to devices and fabrication strategies not possible with top-down methods. This review presents a brief summary of bottom-up and hybrid bottom-up/top-down strategies for nanoelectronics with an emphasis on memories based on the crossbar motif. First, we will discuss representative electromechanical and resistance-change memory devices based on carbon nanotube and core-shell nanowire structures, respectively. These device structures show robust switching, promising performance metrics and the potential for terabit-scale density. Second, we will review architectures being developed for circuit-level integration, hybrid crossbar/CMOS circuits and array-based systems, including experimental demonstrations of key concepts such lithography-independent, chemically coded stochastic demultipluxers. Finally, bottom-up fabrication approaches, including the opportunity for assembly of three-dimensional, vertically integrated multifunctional circuits, will be critically discussed.

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Nanoelectronics from the bottom up

The scaling of complementary metal oxide semiconductor transistors has led to the silicon dioxide layer, used as a gate dielectric, being so thin (14?nm) that its leakage current is too large It is necessary to replace the SiO2 with a physically thicker layer of oxides of higher dielectric constant (?) or 'high K' gate oxides such as hafnium oxide and hafnium silicate These oxides had not been extensively studied like SiO2, and they were found to have inferior properties compared with SiO2, such as a tendency to crystallize and a high density of electronic defects Intensive research was needed to develop these oxides as high quality electronic materials This review covers both scientific and technological issues?the choice of oxides, their deposition, their structural and metallurgical behaviour, atomic diffusion, interface structure and reactions, their electronic structure, bonding, band offsets, electronic defects, charge trapping and conduction mechanisms, mobility degradation and flat band voltage shifts The oxygen vacancy is the dominant electron trap It is turning out that the oxides must be implemented in conjunction with metal gate electrodes, the development of which is further behind Issues about work function control in metal gate electrodes are discussed

https://iopscience.iop.org/article/10.1088/0034-4885/69/2/R02/pdf

High dielectric constant gate oxides for metal oxide Si transistors

Oxygen vacancies in transition metal and rare earth oxides: Current state of understanding and remaining challenges

Whenever a compound crystal is cut normal to a randomly chosen direction, there is an overwhelming probability that the resulting surface corresponds to a polar termination and is highly unstable. Indeed, polar oxide surfaces are subject to complex stabilization processes that ultimately determine their physical and chemical properties. However, owing to recent advances in their preparation under controlled conditions and to improvements in the experimental techniques for their characterization, an impressive variety of structures have been investigated in the last few years. Recent progress in the fabrication of oxide nano-objects, which have been largely stimulated by a growing demand for new materials for applications ranging from micro-electronics to heterogeneous catalysis, also offer interesting examples of exotic polar structures. At odds with polar orientations of macroscopic samples, some smaller size polar nano-structures turn out to be perfectly stable. Others are subject to unusual processes of stabilization, which are absent or not effective in their extended counterparts. In this context, a thorough and comprehensive reflexion on the role that polarity plays at oxide surfaces, interfaces and in nano-objects seems timely.This review includes a first section which presents the theoretical concepts at the root of the polar electrostatic instability and its compensation and introduces a rigorous definition of polar terminations that encompasses previous theoretical treatments; a second section devoted to a summary of all experimental and theoretical results obtained since the first review paper by Noguera (2000 J. Phys.: Condens. Matter 12 R367); and finally a discussion section focusing on the relative strength of the stabilization mechanisms, with special emphasis on ternary compound surfaces and on polarity effects in ultra-thin films.

https://iopscience.iop.org/article/10.1088/0034-4885/71/1/016501/pdf

Polarity of oxide surfaces and nanostructures

Preface. 1. Integrated Circuit Technologies: From Conventional CMOS to the nanoscale era (P. M. Zeitzoff, J. A. Hutchby, G. Bersuker, H. R. Huff). 2. Electronics Below 10 nm (K. Likharev). 3. Lithography: Concepts, Challenges, and Prospects (K. Lucas, S. Postnikov, C. Henderson, S. Hector). 4. Experimental Investigations of the Stability of Candidate Materials for High-K Gate Dielectrics in Silicon-Based MOSFETs (S. Stemmer and D. G. Schlom). 5. Defects in wide-gap oxides: Computer modelling and challenges (A. L Shluger, A. Foster, J.L. Gavartin, P.V. Sushko). 6. Tunneling Through Single Molecules (J. Tomfohr, Jun Li, O. Sankey). 7. Practical Quantum Computing (P. M. Lenahan). Subject. Index.

Nano and Giga Challenges in Microelectronics

The atomic structure, stability and electronic properties of zirconium and hafnium nitrides and oxynitrides (MN, M3N4, and M2N2O; M=Zr, Hf) have been studied using first-principles density functional theory calculations. It is found that the orthorhombic Pnam structure of M3N4, which was observed experimentally for zirconium nitride, is more stable for this stoichiometry than the cubic spinel and rock-salt-type structures. The calculated band structures and electronic densities of states demonstrate that both the MN and M3N4 phases of zirconium and hafnium nitrides in the rock-salt-type structure are characterized by metallic properties, while the orthorhombic structure of the M3N4 phase exhibits an insulating behavior in agreement with experimental observations. The formation of nitrogen vacancies in the insulating M3N4 phase converts it into the metallic MN phase. Calculations of Zr2N2O and Hf2N2O in the cubic Bixbyite-type and hexagonal P3–ml crystal structures predict that these materials are insulato...

Anatoli Korkin

Papers

Nano and Giga Challenges in Microelectronics

Structure and electronic properties of zirconium and hafnium nitrides and oxynitrides

First-principle investigation of the hydroxylation of zirconia and hafnia surfaces

Theoretical ab Initio Study of Neutral and Charged B3Hn (n = 3-9) Species. Importance of Aromaticity in Determining the Structural Preferences

Theoretical Prediction of 2,4,6-Trinitro-1,3,5-triazine (TNTA). A New, Powerful, High-Energy Density Material?