ALD – Atomic Layer Deposition
What is Atomic Layer Deposition (ALD)?
Atomic layer deposition (ALD) is a thin film deposition method using a stepwise application of a chemical process in the gas phase. The method is based on chemical vapour deposition. Most ALD reactions utilize two chemicals called precursors (or „reactants“). These precursors react with the surface of a substrate-material one at a time in a step by step, self-limiting process. By repeating exposure to separate precursors, a thin film will slowly grow. The main application of ALD is in micro-and nanoelectronics int terms of step coverage and thickness uniformity. Further, strongly growing applications are in the fields of photovoltaic, energy storage, and catalyst.
ALD Cycle, based on Cremers et al., 2019
What are typical applications for ALD?
- High-k materials, for instance HfO2 and other oxides
The excellent thickness control of ALD is perfect for this application.
- Ideal for structures with High Aspect Ratio, (>100:1)
- Nanolaminates / Superlattices
- As passivation layer in PV Cells, development of PV cells
- Multilayer systems, for instance materials based on perovskite
- Particle coating
- Coating of porous materials.
Advantages of ALD:
- Layer thickness of a few Nanometer with thickness control <1nm.
- Best uniformity on large area substrates
- Precise control of Stoichiometry
What is Thermal ALD:
Thermal ALD is a deposition process at relatively high temperatures ranging from 150oC to 450oC. It provides high control of thickness, independently of substrate geometry and reactor design.
What is Plasma ALD or PEALD (Plasma Enhanced Atomic Layer Deposition):
Plasma activates the precursors‘ reactivity, allowing the deposition temperature to be lowered without affecting the quality of the film. More precursors can be used, allowing more materials to be deposited and thus more materials to be coated.
Why Atomic Layer Deposition:
The inherent strength of ALD technology is its ability to utilize most of the substances available in the periodic table, as shown below.
Furthermore, conformality and the ability to adapt to various substrates, shapes, and high aspect ratio structures producing uniform, pinhole-free single material and nano-laminate coatings, has created broad interest in many fields.
Arradiance process and equipment technologies were forged in the most challenging ALD Nanofilm environment: electrically functional nanofilms on substrates possessing both high surface areas (>9m2) and high aspect ratios (>>100:1).