Atomic Layer Deposition
The ALD reactor enabled the widespread adoption of atomic layer deposition in research and industry. Reactors come in all shapes, sizes and configurations. Learn how the ALD reactor operates and the types of ALD reactors available.
What is an ALD reactor?
The ALD reactor is just that – a tool in which one performs Atomic Layer Deposition. It is a process engineer’s best friend, and a well-functioning reactor is paramount for performing high-quality atomic layer deposition.
An ALD reactor at its core is a series of valves which control the introduction and exhaust of various gases to a substrate to be coated. While there exists numerous types of ALD reactors (see below), they all share some basic components that allow it to perform ALD processes. Some important components include:
- Precursor sources: Chemicals (solid, liquid, or gas) which will participate in the ALD reactions.
- Reaction chamber: Area where substrates are housed and the ALD process occurs. The reaction chamber is often heated to drive reactions, i.e. thermal ALD.
- Vacuum pump: To bring the pressure down inside the system and provide an easy exhaust path for byproducts and excess precursor. Reactions are usually performed at 1-10 mTorr but can also be done at atmosphere.
- Valving: Various types of valves (pneumatic, solenoid, gate) used to control the flow of precursors and isolate parts of the reactor
- Inert gas: Provides entrainment of precursors through the chamber and of byproducts being purged.
- Computer interface: While ALD can be performed manually, it is typically automated. Designated software or other code is used to automatically operate the open and closing of valves, control precursor pulses, and gather data.
Your most basic ALD reactor, known as a flow tube reactor, works by constantly flowing inert gas through the system. Valves open individual precursor sources and dose them into the inert gas stream which carries the reactant to the substrate. After a sufficient dose is reached, the valve cuts off the source and the inert gas shuttles reaction byproducts and excess precursor to the exhaust. After a short purge to ensure the elimination of pesky CVD reactions, the 2nd precursor is introduced in the same fashion. Simple programming automates this process and repeats it over and over until you have a beautiful, conformal ALD coating!
Types of ALD Reactors
ALD reactors come in all types of configurations depending on the substrate to be coated, materials to be deposited, throughput, in situ characterization capabilities, and several other factors. Generally speaking, reactors can be characterized in one way by the type of ALD reactions, thermal or plasma, being performed, and the way in which precursors are introduced to the substrate, temporally or spatially.
Thermal ALD – Both reactions driven only by the use of heat
Plasma ALD – Uses plasma to help activate the surface for one or more reactions
Temporal ALD – Substrate is stationary and precursors are introduced individually
Spatial ALD – Substrate travels through zones of constantly flowing precursor
Below are some examples of Beneq tools that utilize different combinations of reactions and processes, and the best use cases for each! Learn more about what these ALD reactors are used for on our ALD Applications page.
Batch ALD tools, like the Beneq P800, are a great example of a production-scale reactor using thermal ALD in a temporal fashion. Batch reactors allow the user to coat large numbers of samples all at one time. The batch configuration is a great option when you have large or complex shaped parts or want to coat multiple surfaces simultaneously.
The Beneq Transform® 300 has multiple chambers, one being a single-wafer plasma chamber. Plasmas may be used to pre-clean surfaces and provide alternative pathways to deposition, e.g. low-temperature. Temporal, plasma tools are an excellent way to get high-quality films with clean interfaces – perfect for semiconductor manufacturing.
Spatial tools are the high-throughput powerhouses of ALD equipment for industries outside of semiconductors. A thermal, spatial tool works great for ALD on high surface area or porous substrates. Beneq’s Genesis ALD is a roll-to-roll type reactor that allows web-based substrates, like battery electrodes, to be coated at high speeds.
The plasma version of a spatial ALD tool is realized with the Beneq C2R, which utilizes a turntable that rotates substrates through precursor zones. Plasma, spatial tools work best for rapid, single-sided coatings of rigid substrates, as well as simple nanostructured components. Low-temperature optical coatings are a great application for this type of tool.
Other common types of ALD reactors
The most common types of ALD reactors not mentioned above are reactors which are built for powder ALD. These include rotary reactors, fluidized bed reactors, and continuous coating (spatial set up) reactors. Due to the highly unique surface science associated with particles, they can be exceptionally difficult to coat.