Modeling and in Situ Probing of Surface Reactions in Atomic Layer Deposition (original) (raw)
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Monitoring atomic layer deposition processes in situ and in real-time by spectroscopic ellipsometry
2011
Depositing ultra-thin metallic films with an accurate control of the film properties (like film thickness, surface roughness and electrical properties) both in the initial and in the progressed film growth regime is a critical challenge. Monitoring atomic layer deposition processes by spectroscopic ellipsometry allows film thickness control in the sub-nanometer range. In addition, ellipsometry serves as a powerful technique for process analysis as it covers many relevant issues, like the evaluation of substrate temperatures as well as the quantification of film properties during the entire ALD process (i. e. in all relevant growth regimes).
Atomic Layer Deposition: An Overview
Chemical Reviews, 2010
, and an Alfred P. Sloan Foundation Fellowship (1988). Dr. George's research interests are in the areas of surface chemistry, thin film growth, and nanostructure engineering. He is currently directing a research effort focusing on atomic layer deposition (ALD) and molecular layer deposition (MLD). This research is examining new surface chemistries for ALD and MLD growth, measuring thin film growth rates, and characterizing the properties of thin films. Dr. George served as Chair of the first American Vacuum Society (AVS) Topical Conference on Atomic Layer Deposition (ALD2001) held in Monterey, California. He also teaches a one-day short course on ALD for the AVS. Dr. George is a cofounder of ALD NanoSolutions, Inc., a startup company that is working to commercialize ALD technology.
New development of atomic layer deposition: processes, methods and applications
Science and Technology of Advanced Materials, 2019
Atomic layer deposition (ALD) is an ultra-thin film deposition technique that has found many applications owing to its distinct abilities. They include uniform deposition of conformal films with controllable thickness, even on complex three-dimensional surfaces, and can improve the efficiency of electronic devices. This technology has attracted significant interest both for fundamental understanding how the new functional materials can be synthesized by ALD and for numerous practical applications, particularly in advanced nanopatterning for microelectronics, energy storage systems, desalinations, catalysis and medical fields. This review introduces the progress made in ALD, both for computational and experimental methodologies, and provides an outlook of this emerging technology in comparison with other film deposition methods. It discusses experimental approaches and factors that affect the deposition and presents simulation methods, such as molecular dynamics and computational fluid dynamics, which help determine and predict effective ways to optimize ALD processes, hence enabling the reduction in cost, energy waste and adverse environmental impacts. Specific examples are chosen to illustrate the progress in ALD processes and applications that showed a considerable impact on other technologies.
Journal of the Korean Ceramic Society, 2016
Continued miniaturization and increasingly exact requirements for thin film deposition in the semiconductor industry is driving the search for new effective, efficient, selective precursors and processes. The requirements of defect-free, conformal films, and precise thickness control have focused attention on atomic layer deposition (ALD). ALD precursors so far have been developed through a trial-and-error experimental approach, leveraging the expertise and tribal knowledge of individual research groups. Precursors can show significant variation in performance, depending on specific choice of co-reactant, deposition stage, and processing conditions. The chemical design space for reactive thin film precursors is enormous and there is urgent need for the development of computational approaches to help identify new ligand-metal architectures and functional co-reactants that deliver the required surface activity for next-generation thin-film deposition processes. In this paper we discuss quantum mechanical simulation (e.g. density functional theory, DFT) applied to ALD precursor reactivity and state-of-the-art automated screening approaches to assist experimental efforts leading toward optimized precursors for next-generation ALD processes.
Modeling and simulation of atomic layer deposition at the feature scale
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2002
We present a transient Boltzmann equation based transport and reaction model for atomic layer deposition ͑ALD͒ at the feature scale. The transport model has no adjustable parameters. In this article, we focus on the reaction step and the postreaction purge steps of ALD. The heterogeneous chemistry model consists of reversible adsorption of a reactant on a single site, and irreversible reaction of a second gaseous reactant with the adsorbed reactant. We conduct studies on the effect of the kinetic rate parameter associated with the reaction. We provide results for number densities of gaseous species, fluxes to the surface of the feature, and surface coverage of the adsorbing reactant as functions of time. For reasonable reaction rate parameter values, the time scale for gas transport is much smaller than that for reaction and desorption. For these cases, an analytic expression for the time evolution of the surface coverage of the adsorbing reactant provides a good approximation to the solution obtained from the transport and reaction model. The results show that fractional coverage of the adsorbing reactant reduces significantly in the reaction step due to reaction with the gaseous reactant and desorption. Larger values of the reaction rate parameter lead to larger reductions in the fractional coverage during the reaction step. For smaller values of the reaction rate parameter, the decrease in coverage is dominated by desorption. The surface coverage of the adsorbing reactant also decreases during purge steps, due to desorption.
REM studies of surface dynamics: growth of Ge on Au-deposited Si(111) surfaces
Ultramicroscopy, 1993
Growth of Ge on Si(111)"5 x 2"-Au surfaces was studied by ultra-high-vacuum reflection electron microscopy (UHV-REM) and diffraction (RHEED). Segregation of Au atoms to the topmost surface during Ge deposition was observed resulting in the formation of a ~ x ~/3 structure. The structure retained during the subsequent deposition of Ge was accompanied by a change of lattice constant of the a/3-x v~-structure from that of Si to that of Ge. Step growth of Ge was enhanced by the presence of Au atoms. Formation of 3D islands of Ge was suppressed on Au-deposited surfaces. However, the suppression was not complete.
In situ spectroscopic ellipsometry for atomic layer deposition
2009
The application of in situ spectroscopic ellipsometry during thin film synthesis by atomic layer deposition (ALD) is examined for results obtained on Al 2 O 3 , TaN x , and TiN films with thicknesses ranging from 0.1 to 100 nm. By analyzing the film thickness and the energy dispersion of the optical constants of the films, the layer-by-layer growth and material properties of the ALD films can be studied in detail. The growth rate per cycle and the nucleation behavior of the films can be addressed by monitoring the thickness as a function of the number of cycles. It is shown that from the energy dispersion relation, insight into the conductive properties of metallic films can be derived. Moreover, the shape of the dispersion relation can be used to discriminate between different material compositions.
Nanotechnology Reviews, 2022
The use of computational modelling and simulation methodologies has grown in recent years as researchers try to understand the atomic layer deposition (ALD) process and create new microstructures and nanostructures. This review article explains and simplifies two simulation methodologies, molecular dynamics and the density functional theory (DFT), in solving atomic layer deposition problems computationally. We believe that these simulation methodologies are powerful tools that can be utilised in atomic layer deposition. DFT is used to solve problems in surface science and catalysis (predicting surface energy, adsorption energy, charge transfer, etc.), semiconductors (band structure, defect bands, band gap, etc.), superconductors (electron–phonon coupling, critical transition temperature), and molecular electronics (conductance, current–voltage characteristics). Molecular dynamics (MD) is used to predict the kinetic and thermodynamic properties of a material. Of interest in this arti...