Atomic Layer Deposition (Chapter in Kirk-Othmer Encyclopedia of Chemical Technology)
- J. Ruud van Ommen,Aristeidis Goulas,Riikka L. Puurunen
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Atomic layer deposition (ALD) is a gas-phase method to grow layers of solid materials with subnanometer precision. It has been invented independently in the Soviet Union in the 1960s under the name molecular layering, and in the 1970s in Finland under the name atomic layer epitaxy. ALD relies on alternatingly exposing a surface to gaseous reactants—separated by a purge step—that react in a self-terminating manner. This article introduces the fundamentals of the surface chemistry of ideal ALD, including saturating and irreversible reactions, growth per cycle, monolayer concepts relevant to ALD, typical surface reaction mechanisms, saturation-limiting factors, growth modes, area-selective ALD, growth kinetics, and conformality. It also discusses typical deviations from ideal ALD. Over the years, many different ALD process chemistries have been developed. A range of reactor systems is available, depending on the type of substrate and required productivity. ALD is broadly applicable in practice since it couples nanoscale precision with a good scalability and can be used to deposit a large variety of materials. In recent years, the interest in ALD has been growing strongly. The most important sector regarding commercial applications of ALD is currently the semiconductor industry.