Chinese
EnglishAtomic Layer Deposition vs. Chemical Vapor Deposition
Thin film deposition is critical to the manufacture of many optoelectronic, solid-state, and medical devices, including consumer electronics, lasers, LED displays, optical filters, microanalytical specimen slides, and medical implants. 1
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Atomic layer deposition (ALD) and chemical vapor deposition (CVD) are widely used deposition techniques. This article explores both methods and compares their uses, advantages, and disadvantages.
ALD vs. CVD: Process Mechanisms
The term “ALD” was first used around 2000. The technique achieves atomic layer controlled and conformal deposition via a continuous self-limiting surface reaction. It involves sequentially introducing chemical reagents to a substrate surface to form a sub-monolayer film. 2
ALD is primarily used for films below 100 nanometers, but can also be used for thicker films up to several micrometers. In this process, two or more precursors react sequentially with a substrate in a chamber at a specific temperature and pressure, depositing the material layer by layer on the substrate surface. 2
The ALD cycle typically consists of four phases: introduction of reactants, purging of excess reactants with an inert gas, addition of counter-reactants, and purging of unused reactants and byproducts. 3
CVD, on the other hand, is a vacuum-based method for manufacturing high-quality, high-performance solid materials. It is widely used in materials processing to form thin layers on heated substrates using vapor phase precursors in a chemical reaction.
The substrate reacts with one or more volatile precursors, which decompose on the surface of the substrate material, thereby depositing a thin film. 4 In simple terms, the gas mixture interacts with the substrate surface, causing some of the gas components to chemically decompose, forming a solid coating on the material surface.
ALD involves sequential pulses of precursors, while CVD involves continuous chemical reactions through the simultaneous introduction of reactants. The sequential process of ALD ensures self-limiting precursor adsorption, distinguishing it from simultaneous reactions in CVD.
Applications and Benefits of ALD and CVD
ALD is ideal for highly consistent ultra-thin films. It is used for nanopatterning in microelectronics, energy storage systems, desalination, catalysis, and medical fields. Industrial applications include gyroscopes, accelerometers, nanomachines, GPS navigation, thin film magnetic heads (TFMH), and passive electrical devices.
ALD is also used to coat porous materials, nanomaterials, and nanoparticles, such as lithium battery cathode materials and desalination membranes. 5 In addition, ALD helps prevent environmental pollution and is used in the fields of water purification and gas separation.
CVD is suitable for thicker films and is mainly used in the semiconductor industry to make materials for solar panels, LEDs, perovskite batteries, and integrated circuits for devices such as mobile phones and TVs. It is also used to prepare single-crystalline metal oxides such as sapphire and ferrite, and to produce specific shapes such as tubes by removing the substrate. 6
Previously, coating lenses and other optical devices with thin films was a challenge due to elasticity issues and difficulties with uneven surfaces. Researchers have made a major breakthrough by using a new ALD method to coat ultra-black coatings on uneven lens surfaces for space exploration microscopes. 7
This upgraded coating is more resilient and efficient than previous versions. This durable ultra-black thin film coating is designed for aerospace-grade magnesium alloys, which is essential for space exploration where weight and durability are critical.
Current coating technologies use brittle materials that cannot withstand harsh environments. This new type of coating is very effective for space exploration and optics, and can also be applied to solar cells and energy storage, significantly improving efficiency.
Main Challenges
Despite the widespread application of these technologies, there are still some challenges that hinder their application.
ALD can produce high-quality films with excellent consistency, but its high precision usually results in a large amount of precursor gas and energy consumption. In the ALD process, about 60% of the precursor dose is wasted, and concerns have been raised about its economic viability due to the low material utilization efficiency of about 50.4%.
CVD, while widely used, requires precise control of temperature, pressure, and chemical reactions, making it more challenging to implement than ALD. The equipment required for CVD is expensive, especially for large-scale production, which affects the overall production efficiency. In addition, the use of CVD to coat large and bulky structures is limited due to the size restrictions of the reaction chamber. 8
There are efforts to make deposition technologies more environmentally friendly. The development of CVD chemistries that use lower energy input for precursor reactions and fewer harmful byproducts is a promising step towards sustainable practices.
Additionally, designing CVD reactors with minimal vacuum volumes and thermal budgets combined with the recycling of process gases can reduce energy consumption and improve atomic efficiency. 9
Future Outlook
With the advancement of miniaturization in recent years, the applications of ALD and CVD processes have become more widespread. As devices become smaller and more complex, the precision and controllability of these deposition processes have become indispensable.
The pursuit of more efficient energy storage solutions has brought ALD into the spotlight, significantly improving the performance and lifetime of energy storage devices. 10
For example, atmospheric pressure ALD is an emerging technology that aims to revolutionize the commercial production of large-area substrates and open new applications for high-porosity and 3D materials. The technology is expected to achieve high substrate throughput and shorten reaction times, thereby improving manufacturing efficiency in various industries.
As researchers continue to prioritize ALD and CVD technologies for renewable energy and efficient energy storage, significant progress will be made to make these methods environmentally friendly and cost-effective.