Atomic layer deposition

Atomic Layer Deposition (ALD) is a gas phase chemical process used to create extremely thin coatings. The majority of ALD reactions use two chemicals, typically called precursors. These precursors react with a surface one-at-a-time in a sequential manner. By exposing the precursors to the growth surface repeatedly, a thin film is deposited.^[1]

Additional recommended knowledge

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Introduction

ALD is a self-limiting, sequential surface chemistry that deposits conformal thin-films of materials onto substrates of varying compositions. ALD is similar in chemistry to chemical vapor deposition (CVD), except that the ALD reaction breaks the CVD reaction into two half-reactions, keeping the precursor materials separate during the reaction. ALD film growth is self-limited and based on surface reactions, which makes achieving atomic scale deposition control possible. By keeping the precursors separate throughout the coating process, atomic layer control of film grown can be obtained as fine as ~ 0.1 angstroms per monolayer.

ALD has unique advantages over other thin film deposition techniques, as ALD grown films are conformal, pin-hole free, and chemically bonded to the substrate. With ALD it is possible to deposit coatings perfectly uniform in thickness inside deep trenches, porous media and around particles. The film thickness range is usually 1-500 nm.

ALD can be used to deposit several types of thin films, including various ceramics, from conductors to insulators.

See also

• Atomic layer epitaxy
• Chemical vapor deposition

References