Surface chemistry of atomic layer deposition: A case study for the trimethylaluminum/water process
TL;DR: In this paper, the surface chemistry of the trimethylaluminum/water ALD process is reviewed, 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.
Abstract: 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.
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4,756 citations
TL;DR: In this article, a review of the development of high-k gate oxides such as hafnium oxide (HFO) and high-K oxides is presented, with the focus on the work function control in metal gate electrodes.
Abstract: 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
1,520 citations
TL;DR: A practical synthesis method to produce isolated single platinum atoms and clusters using the atomic layer deposition technique and indicates that the partially unoccupied density of states of the platinum atoms' 5d orbitals on the nitrogen-doped graphene are responsible for the excellent performance.
Abstract: Platinum-based catalysts have been considered the most effective electrocatalysts for the hydrogen evolution reaction in water splitting. However, platinum utilization in these electrocatalysts is extremely low, as the active sites are only located on the surface of the catalyst particles. Downsizing catalyst nanoparticles to single atoms is highly desirable to maximize their efficiency by utilizing nearly all platinum atoms. Here we report on a practical synthesis method to produce isolated single platinum atoms and clusters using the atomic layer deposition technique. The single platinum atom catalysts are investigated for the hydrogen evolution reaction, where they exhibit significantly enhanced catalytic activity (up to 37 times) and high stability in comparison with the state-of-the-art commercial platinum/carbon catalysts. The X-ray absorption fine structure and density functional theory analyses indicate that the partially unoccupied density of states of the platinum atoms’ 5d orbitals on the nitrogen-doped graphene are responsible for the excellent performance. Downsizing platinum based nanocatalysts has the twin advantages of lower platinum usage and increased activity per platinum atom. Here, the authors report an atomic layer deposition technique for single platinum atom catalyst fabrication and assess their hydrogen evolution activity.
1,374 citations
TL;DR: Atomic layer deposition (ALD) is a vapor phase technique capable of producing thin films of a variety of materials as discussed by the authors, including metal oxides such as Zn1−xSnxOy, ZrO2, Y2O3, and Pt.
1,280 citations
TL;DR: Puurunen et al. as discussed by the authors summarized the two-reactant ALD processes to grow inorganic materials developed to-date, updating the information of an earlier review on ALD.
Abstract: 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.
1,160 citations
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TL;DR: In this paper, a review of the literature in the area of alternate gate dielectrics is given, based on reported results and fundamental considerations, the pseudobinary materials systems offer large flexibility and show the most promise toward success.
Abstract: Many materials systems are currently under consideration as potential replacements for SiO2 as the gate dielectric material for sub-0.1 μm complementary metal–oxide–semiconductor (CMOS) technology. A systematic consideration of the required properties of gate dielectrics indicates that the key guidelines for selecting an alternative gate dielectric are (a) permittivity, band gap, and band alignment to silicon, (b) thermodynamic stability, (c) film morphology, (d) interface quality, (e) compatibility with the current or expected materials to be used in processing for CMOS devices, (f) process compatibility, and (g) reliability. Many dielectrics appear favorable in some of these areas, but very few materials are promising with respect to all of these guidelines. A review of current work and literature in the area of alternate gate dielectrics is given. Based on reported results and fundamental considerations, the pseudobinary materials systems offer large flexibility and show the most promise toward success...
5,711 citations
Book•
01 Jan 1986
TL;DR: In this paper, the authors present an approach to scale-up of a continuous-flow-reactor with a CSTR design and demonstrate the performance of the CSTRs.
Abstract: 1. Mole Balances. The Rate of Reaction The General Mole Balance Equation Batch Reactors Continuous-Flow Reactors Industrial Reactors Summary CD-ROM Material Questions and Problems Supplementary Reading 2. Conversion and Reactor Sizing. Definition of Conversion Batch Reactor Design Equations Design Equations for Flow Reactors Applications of the Design Equations for Continuous-Flow Reactors Reactors in Series Some Further Definitions Summary CD-ROM Materials Questions and Problems Supplementary Reading 3. Rate Laws and Stoichiometry. Part 1. Rate Laws Basic Definitions The Reaction Order and the Rate Law The Reaction Rate Constant Present Status of Our Approach to Reactor Sizing and Design Part 2. Stoichiometry Batch Systems Flow Systems Summary CD-ROM Material Questions and Problems Supplementary Reading 4. Isothermal Reactor Design. Part 1. Mole Balances in Terms of Conversion Design Structure for Isothermal Reactors Scale-Up of Liquid-Phase Batch Reactor Data to the Design of a CSTR Design of Continuous Stirred Tank Reactors (CSTRs) Tubular Reactors Pressure Drop in Reactors Synthesizing the Design of a Chemical Plant Part 2. Mole Balances Written in Terms of Concentration and Molar Flow Rate Mole Balances on CSTRs, PFRs, PBRs, and Batch Reactors Microreactors Membrane Reactors Unsteady-State Operation of Stirred Reactors The Practical Side Summary ODE Solver Algorithm CD-ROM Material Questions and Problems Some Thoughts on Critiquing What You read Journal Critique Problems Supplementary Reading 5. Collection and Analysis of Rate Data. The Algorithm for Data Analysis Batch Reactor Data Method of Initial Rates Method of Half-Lives Differential Reactors Experimental Planning Evaluation of Laboratory Reactors Summary CD-ROM Material Questions and Problems Journal Critique Problems Supplementary Reading 6. Multiple Reactions. Definitions Parallel Reactions Maximizing the Desired Product in Series Reactions Algorithm for Solution of Complex Reactions Multiple Reactions in a PFR/PBR Multiple Reactions in a CSTR Membrane Reactors to Improve Selectivity in Multiple Reactions Complex Reactions of Ammonia Oxidation Sorting It All Out The Fun Part Summary CD-ROM Material Questions and Problems Journal Critique Problems Supplementary Reading 7. Reaction Mechanisms, Pathways, Bioreactions, and Bioreactors. Active Intermediates and Nonelementary Rate Laws Enzymatic Reaction Fundamentals Inhibition of Enzyme Reactions Bioreactors Physiologically Based Pharmacokinetic (PBPK) Models Summary CD-ROM Material Questions and Problems Journal Critique Problems Supplementary Reading 8. Steady-State Nonisothermal Reactor Design. Rationale The Energy Balance Adiabatic Operation Steady-State Tubular Reactor with Heat Exchange Equilibrium Conversion CSTR with Heat Effects Multiple Steady States Nonisothermal Multiple Chemical Reactions Radial and Axial Variations in a Tubular Reactor The Practical Side Summary CD-ROM Material Questions and Problems Journal Critique Problems Supplementary Reading 9. Unsteady-State Nonisothermal Reactor Design. The Unsteady-State Energy Balance Energy Balance on Batch Reactors Semibatch Reactors with a Heat Exchanger Unsteady Operation of a CSTR Nonisothermal Multiple Reactions Unsteady Operation of Plug-Flow Reactors Summary CD-ROM Material Questions and Problems Supplementary Reading 10. Catalysis and Catalytic Reactors. Catalysts Steps in a Catalytic Reaction Synthesizing a Rate Law, Mechanism, and Rate-Limiting Step Heterogeneous Data Analysis for Reactor Design Reaction Engineering in Microelectronic Fabrication Model Discrimination Catalyst Deactivation Summary ODE Solver Algorithm CD-ROM Material Questions and Problems Journal Critique Problems Supplementary Reading 11. External Diffusion Effects on Heterogeneous Reactions. Diffusion Fundamentals Binary Diffusion External Resistance to Mass Transfer What If ... ? (Parameter Sensitivity) The Shrinking Core Model Summary CD-ROM Material Questions and Problems Supplementary Reading 12. Diffusion and Reaction. Diffusion and Reaction in Spherical Catalyst Pellets Internal Effectiveness Factor Falsified Kinetics Overall Effectiveness Factor Estimation of Diffusion- and Reaction-Limited Regimes Mass Transfer and Reaction in a Packed Bed Determination of Limiting Situations from Reaction Data Multiphase Reactors Fluidized Bed Reactors Chemical Vapor Deposition (CVD) Summary CD-ROM Material Questions and Problems Journal Article Problems Journal Critique Problems Supplementary Reading 13. Distributions of Residence Times for Chemical Reactors. General Characteristics Part 1. Characteristics and Diagnostics Measurement of the RTD Characteristics of the RTD RTD in Ideal Reactors Diagnostics and Troubleshooting Part 2. Predicting Conversion and Exit Concentration Reactor Modeling Using the RTD Zero-Parameter Models Using Software Packages RTD and Multiple Reactions Summary CD-ROM Material Questions and Problems Supplementary Reading 14. Models for Nonideal Reactors. Some Guidelines Tanks-in-Series (T-I-S) Model Dispersion Model Flow, Reaction, and Dispersion Tanks-in-Series Model Versus Dispersion Model Numerical Solutions to Flows with Dispersion and Reaction Two-Parameter Models-Modeling Real Reactors with Combinations of Ideal Reactors Use of Software Packages to Determine the Model Parameters Other Models of Nonideal Reactors Using CSTRs and PFRs Applications to Pharmacokinetic Modeling Summary CD-ROM Material Questions and Problems Supplementary Reading Appendix A: Numerical Techniques. Appendix B: Ideal Gas Constant and Conversion Factors. Appendix C: Thermodynamic Relationships Involving the Equilibrium Constant. Appendix D: Measurement of Slopes on Semilog Paper. Appendix E: Software Packages. Appendix F: Nomenclature. Appendix G: Rate Law Data. Appendix H: Open-Ended Problems. Appendix I: How to Use the CD-ROM. Appendix J: Use of Computational Chemistry Software Packages. Index. About the CD-ROM.
3,843 citations
Book•
01 Jan 1976
TL;DR: The Periodic Table and the Chemistry of the Elements as discussed by the authors are the main sources of information about the transition elements of the periodic table and their relationships with the transition metal complexes with TT-Acceptor (TT-Acid) ligands.
Abstract: FIRST PRINCIPLES Some Preliminaries The Electronic Structure of Atoms Structure and Bonding in Molecules Ionic Solids The Chemistry of Selected Anions Coordination Chemistry Solvents, Solutions, Acids and Bases The Periodic Table and the Chemistry of the Elements THE MAIN GROUP ELEMENTS Hydrogen The Group IA(1) Elements: Lithium, Sodium, Potassium, Rubidium and Cesium The Group IIA(2) Elements: Beryllium, Magnesium, Calcium, Strontium and Barium Boron The Group IIIB(13) Elements: Aluminum, Gallium, Indium and Thallium Carbon The Group IVB(14) Elements: Silicon, Germanium, Tin and Lead Nitrogen The Group VB(15) Elements: Phosphorus, Arsenic, Antimony and Bismuth Oxygen The Group VIB(16) Elements: Sulfur, Selenium, Tellurium and Polonium The Halogens: Fluorine, Chlorine, Bromide and Astatine The Noble Gases Zinc, Cadmium and Mercury THE TRANSITION ELEMENTS Introduction to Transition Elements: Ligand Field Theory The Elements of the First Transition Series The Elements of the Second and Third Transition Series Scandium, Yttrium, Lanthanum and the Lanthanides The Actinide Elements SOME SPECIAL TOPICS Metal Carbonyls and Other Transition Metal Complexes with TT-Acceptor (TT-Acid) Ligands Organometallic Compounds Stoichiometric and Catalytic Reactions of Organometallic Compounds Bio-Inorganic Chemistry Index.
2,102 citations
TL;DR: Aluminas have been used extensively as adsorbenu and active catalysrs and catalyst supponsm the pas as discussed by the authors, and they are used as catalysts for the larter process LS also caralyzed by molybdena-alumina.
Abstract: Aluminas have been used extensively as adsorbenu and active catalysrs and catalyst supponsm the pas. Already in 1197 the aluminadyzed dehydration of ettllnoi was dtscavered by Dutch chermsts: and S;rbatier [3] remewed the use of dumlnas as active cazaiysrs far vanous reacttons UI the second decade of thu century. She that time the applicazions of aluuuas m dycic pmcesses have mcreased tremendously. In tndustrral cualytic pmcesses, alumuus are mostiy used as catalyst suppons [4]. Oxides a d mued oxides ap well as tracuuion mauls and noble meare supported oa alumma. Thuscb. romaa-elumana catalysts are ktng used for the conversion of parafdns to olailnrc hydrocarbons, 10 hydrodealkplation of aromatics. and to a lesser exzm in catalyzic reforming. The larter process LS also caralyzed by molybdena-alumina, a cavlyst system whid is also active for malang toluene and ocher aromatics from satwed hydrocarc bons. It also dyzes the Isomerhation of pm. Great efions are presently be-made to nudy the surface c...
1,665 citations
TL;DR: In this article, the choice of oxides, their structural and metallurgical behaviour, atomic diffusion, their deposition, interface structure and reactions, their electronic structure, bonding, band offsets, mobility degradation, flat band voltage shifts and electronic defects are discussed.
Abstract: The scaling of complementary metal oxide semiconductor (CMOS) transistors has led to the silicon dioxide layer used as a gate dielectric becoming so thin (1.4 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 (κ) or 'high K' gate oxides such as hafnium oxide and hafnium silicate. Little was known about such oxides, and it was soon found that in many respects they have inferior electronic properties to SiO2 ,s uch as a tendency to crystallise and a high concentration of electronic defects. Intensive research is underway to develop these oxides into new high quality electronic materials. This review covers the choice of oxides, their structural and metallurgical behaviour, atomic diffusion, their deposition, interface structure and reactions, their electronic structure, bonding, band offsets, mobility degradation, flat band voltage shifts and electronic defects. The use of high K oxides in capacitors of dynamic random access memories is also covered.
1,500 citations