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Atomic Layer Deposition (ALD) is a thin-film deposition technique in which each chemical reactant gas is injected in a sequential pulse form to suppress the gas-phase reaction and a thin film is formed by surface reactions through the self-limited adsorption process on the substrate surface. Since the thickness of the entire deposited film is controlled through the number of deposition cycles, it is easy to control the thickness in atomic-layer units.

ALD Process

Precursor Adsorption and Purge

A precursor containing the substance to be deposited is adsorbed on the substrate surface. In this process, self-limiting adsorption proceeds with the ligands of the precursor, and the adsorption does not progress any more after a certain amount of molecules are adsorbed. The physical adsorption between the precursors can be easily separated since their binding force is weak. On the other hand, the precursors chemically adsorbed on the substrate are more strongly bound. As a result, in the next purge step, all the precursors physically adsorbed are separated and removed, but the chemically absorbed precursors remain adsorbed. Such a difference between chemical absorption and physical adsorption makes it possible to control the atomic-layer scale.

Reactant Reactions and Purge

When each reactant is supplied to form a desired thin film, the reactant and the precursor adsorbed on the substrate are subjected to a surface chemical reaction to form a film. The physically adsorbed reactants and by-products are removed in the subsequent purging process, and the film grows as much as the atomic layer. Such a process constitutes one cycle, and the deposition rate is usually below a monolayer per cycle due to the size effect of the ligand. Since the ALD utilizes surface reactions and requires alternating injections of materials, it has a disadvantage that the deposition rate is slow. However, since the deposition proceeds through the surface reaction while showing perfect step coverage, it is possible to deposit a high-quality thin film at a relatively low temperature through selection of each appropriate precursor and reactant.

Advantages of ALD

TiO2 nano tube
by Lucida™ D100 ALD

Advantages of ALD

·Very high film quality
·Thickness control in an atomic scale
·No particles and no pinholes
·Low temperature process
·Excellent conformality
  - Ability to follow complex and 3D geometries

·Wide range of materials
  - Oxides, nitrides, sulfides, ...
  - Metals
  - Hybrid organic-inorganic materials
  - Even polymers
·Wide range of materials
·Mass production with batch type ALD

Al2O3 film with conformal
step coverage of 32:1
aspect by
Lucida™ D100 ALD

ALD Technology application field

·Solar cell
·Flexible OLED display
·OLED light
·LED coating
·Optical coating

·Antimicrobial coating
·Secondary battery
·Various nano application technologies

See Technology reports for more information.