Atomic layer deposition and how it works.
Atomic Layer Deposition
Atomic layer deposition, ALD, is a thin film technology that enables new and highly competitive products. ALD is also a powerful resource for advanced nanotechnology research. Typical applications of ALD contain a requirement to manufacture very precise nanometer–thick, pinhole–free and totally conformal thin films on any shape and geometry. For today’s businesses, Beneq ALD offers the necessary tools to accelerate growth, by means of new and innovative applications, production equipment you can count on and affordable cost of ownership.
ALD, a chemical vapor deposition (CVD) method, was initially developed for manufacturing nanolaminate insulators (Al2O3/TiO2) and zinc sulfide (ZnS) phosphor films for thin film electroluminescent (TFEL) displays. Large–scale production of these displays started in the mid–1980’s, mainly thanks to ALD. The unique properties of the coatings, together with the high repeatability, were the main factors leading to successful industrial production.
How ALD works
ALD is an enabling technology for new and improved products. It provides coatings and material features which either cannot be achieved cost–efficiently with existing techniques, or they cannot be achieved at all. ALD, as a thin film coating method, offers:
- Precise control of the film thickness, at true nanometer scale
- Pinhole–free films for, e.g., superior barriers and surface passivation
- Conformal coating of batches, large–area substrates and complex 3D objects, including porous bulk materials, as well as powders
- Engineered and new functional materials and structures, such as nanolaminates
- A highly repeatable and scalable process.
Further reading: ALD on Aalto OpenLearning
ALD coating process
ALD is based on surface controlled thin film deposition. During coating, two or more chemical vapors or gaseous precursors react sequentially on the substrate surface, producing a solid thin film (see schematic below). Most ALD coating systems utilize a flow–through traveling wave setup, where an inert carrier gas flows through the system and precursors are injected as very short pulses into this carrier flow. The carrier gas flow takes the precursor pulses as sequential “waves” through the reaction chamber, followed by a pumping line, filtering systems and, eventually, a vacuum pump.
Typical process conditions:
- Pressure range: 0.1–10 mbar (Torr, hPa) or atmospheric
- Temperature: typically, 50 – 500 °C
Process and coating properties
Excellent adhesion: Chemisorption of precursors with the surface provides excellent adhesion.
Saturation: Self–terminating surface reactions enable automatic processing and eliminate the need for over–precise dosing and continuous operator attendance.
Sequential: Digital–like sequential growth provides for excellent accuracy without the need for extensive in situ feedback or operator attendance.
Surface–controlled reactions: Surface reactions enable unconditionally conformal coatings, regardless of if the substrate is dense, porous, tubular, a powder or otherwise complex in shape.
Precise and repeatable: Film growth thickness during a single ALD cycle is process specific, but typically about 1 Å (0.1 nm).
Thin, dense, and smooth: ALD enables depositing layers less than one nanometer in thickness. Coatings as thin as 0.8 nm are currently used in certain industrial applications.
High capacity: The surface–controlled growth feature allows for capacity expansion for both large batches and large surfaces.
Plasma enhanced ALD: ALD coating can also be modified by applying plasma to the deposition cycle, e.g., to enable coating with certain metals and low–temperature oxides and nitrides.
Roll–to–Roll and Continuous ALD: Roll–to–Roll coating opens the door for many new ALD applications in, for example, the flexible electronics industry. Beneq, with the world’s first commercially available research platform for continuous ALD, is at the forefront of this development work.
ALD on particles and powders: Combining conformal coating with particulate substrates creates completely new opportunities to, for example, modify the diffusion properties of battery materials and much more.
The most common materials deposited by ALD include (selection):
Oxides: Al2O3, CaO, CuO, Er2O3, Ga2O3, HfO2, La2O3, MgO, Nb2O5, Sc2O3, SiO2, Ta2O5, TiO2, VXOY, Y2O3, Yb2O3, ZnO, ZrO2, etc.
Nitrides: AlN, GaN, TaNX, TiAlN, TiNX, etc.
Carbides: TaC, TiC, etc.
Metals: Ir, Pd, Pt, Ru, etc.
Sulfides: ZnS, SrS, etc.
Fluorides: CaF2, LaF3, MgF2, SrF2, etc.
Biomaterials: Ca10(PO4)6(OH)2 (hydroxyapatite)
Polymers: PMDA–DAH, PMDA–ODA, etc.
Doping, nanolaminates and mixed structures: ALD enables a vast array of material combinations.
There are many more materials and processes available in ALD today. Beneq ALD specialists are at your service, if you have any inquiries. See R&D Services for more information.