Atomic layer deposition (ALD)

Atomic layer deposition (ALD) is a technique for applying very thin coatings to surfaces. This process belongs to the family of CVD methods. With ALD, the coating is formed by repeated, cyclical reactions on the surface.

This method is primarily used in semiconductor electronics, for example, to create special coatings in certain transistors. However, the technology is also used in other areas – such as the production of small mechanical systems, barrier coatings, or optical coatings. 

In contrast to typical CVD processes, in which the chemical reaction takes place everywhere in the room, the reaction with ALD only takes place directly on the surface. It concerns a step-by-step process: First, a substance is applied to the surface, where it reacts. This substance is then removed, and another substance is applied, which reacts there again. This is repeated until the desired coating thickness is achieved. The chamber is cleaned after each step. Only a very thin film is deposited in each of these cycles. Thanks to ALD, uniform, very thin coatings can be produced on complex surfaces. This is achieved at relatively low temperatures of between 150 °C and 400 °C. Sometimes, special techniques or materials are used to reduce the required temperature even further. 

The primary area of application was (and remains) semiconductor electronics, for example, the production of High-k-Gate coatings in MOSFETs. However, the advantages of ALD technology are also increasingly being utilized in other sectors – including the production of MEMS, barrier coatings, optical coatings, or functional coatings on particles or in capillaries.

Atomic layer deposition offers several advantages over other thin film deposition techniques:

1. Atomic precision: ALD enables the deposition of materials, coating by coating, allowing precise and controlled coating thicknesses to be achieved at the atomic level.
2. Surface conformity: The ALD process ensures excellent coverage, even on structured or highly topographical surfaces, thereby resulting in uniform and homogeneous coatings.
3. Low processing temperature: Many ALD processes can be performed at temperatures lower than other CVD processes, rendering them suitable for temperature-sensitive substrates.
4. Wide choice of materials: ALD can be used on a variety of materials – including metals, oxides, and nitrides, making it versatile for a wide range of applications.
5. High levels of quality and purity: Thanks to the sequential process of ALD, high-purity coatings with minimal defects or impurities are produced.
6. Scalability for industrial applications: Despite its atomic precision, ALD can be efficiently scaled for use in industrial production environments, especially in semiconductor electronics.

Thanks to these properties, ALD has established itself as a key process in many areas of materials science and technology.