page_title: Atomic layer deposition
section_title: Introduction
hierarchical_section_title: Atomic layer deposition / Introduction
caption_attribution_description: English: An overview of the materials synthesized by ALD with 1 or more publications describing the process
context_page_description: Atomic layer deposition is a thin-film deposition technique based on the sequential use of a gas phase chemical process; it is a subclass of chemical vapour deposition. The majority of ALD reactions use two chemicals called precursors. These precursors react with the surface of a material one at a time in a sequential, self-limiting, manner. Through the repeated exposure to separate precursors, a thin film is slowly deposited. ALD is a key process in the fabrication of semiconductor devices, and part of the set of tools
  available for the synthesis of nanomaterials.
context_section_description: During atomic layer deposition a film is grown on a substrate by exposing its surface to alternate gaseous species (typically referred to as precursors). In contrast to chemical vapor deposition, the precursors are never present simultaneously in the reactor, but they are inserted as a series of sequential, non-overlapping pulses. In each of these pulses the precursor molecules react with the surface in a self-limiting way, so that the reaction terminates once all the reactive sites on the surface are consumed. Consequently, the maximum amount of material deposited on the surface after a single exposure to all of the precursors (a so-called ALD cycle) is determined by the nature of the precursor-surface interaction. By varying the number of cycles it is possible to grow materials uniformly and with high precision on arbitrarily complex and large substrates.
  ALD is considered one deposition method with great potential for producing very thin, conformal films with control of the thickness and composition of the films possible at the atomic level. A major driving force for the recent interest is the prospective seen for ALD in scaling down microelectronic devices according to Moore's law. ALD is an active field of research, with hundreds of different processes published in the scientific literature, though some of them exhibit behaviors that depart from that of an ideal ALD process. Currently there are several comprehensive review papers that give a summary of the published ALD processes, including the work of Puurunen, Miikkulainen et al., 
  Knoops et al., and Mackus & Schneider et al.. An interactive, community driven database of ALD processes is also available online which generates an up-to-date overview in the form of an annotated periodic table.
  The sister technique of atomic layer deposition, molecular layer deposition (MLD), is employed when organic precursors are wished to be used. By combining the ALD/MLD techniques, it is possible to make highly conformal and pure hybrid films for many applications.
caption: An overview of the materials synthesized by ALD with 1 or more publications describing the process, an up-to-date figure can be obtained online [3] under the Creative Commons license for general use.
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