Revolutionizing the Microelectronics Industry One Atomic Layer at a Time

Written by: Vamseedhara Vemuri, Materials Science and Engineering Department, Lehigh University

Source of cover image: Adobe Stock 

If you take a moment and reflect on the capabilities of your current mobile phone, you will quickly realise that it outperforms a personal computer, professional camera and also has better resolution than a television from a decade ago. You can also observe the enhancement in capabilities of other modern consumer electronics.  

The key driver for this innovation is the ability to shrink the dimensions of integrated circuits (IC’s) in electronic devices. An IC is a miniature electronic circuit that comprises a collection of electronic devices like transistors and capacitors fabricated onto a small semiconductor material, typically silicon. Transistors are miniature semiconductor devices that enable the processing and manipulation of electrical signals, which are essential for controlling the operation of electronic devices; whereas capacitors are electronic components that store and release electrical energy. Both transistors and capacitors are crucial components in IC’s.

(Source of figure: https://www.computerhistory.org/siliconengine/)

Like architecture in the cities where the floors are stacked vertically to efficiently use space, the architecture of the transistors has been continuously modified in almost every generation to be able to fit more electrical components in the same area on ICs. New architectures of transistors are usually followed by thinner and smaller components like capacitors and insulators. This process of shrinking devices is called scaling and is usually beneficial to make devices faster and more efficient. 

(Source of figure: https://www.appliedmaterials.com/us/en/blog/blog-posts/new-innovations-needed-to-continue-scaling-advanced-logic.html)

One of the most impressive examples of this trend is Apple’s M1 processor. The M1 processor is the first chip from Apple to be built on a 5-nanometer manufacturing process. It packs 16 billion transistors into a very small space and has 7% more transistors than its predecessors. Hence, the M1 processor has a significant performance advantage over its predecessors and allows Apple to design devices that are thinner and lighter than ever before.

The ability to shrink component dimensions is not just limited to processors. It is also being used in other areas of consumer electronics, such as displays, batteries, and cameras. As this technology continues to develop, we can expect to see even more amazing devices in the years to come. However, achieving precise miniaturization necessitates meticulous techniques capable of depositing materials at the nanometer scale, ensuring utmost precision on complex geometries and architectures. Atomic layer deposition (ALD) is one such technique that can be used to deposit a wide variety of materials on atomic scale (few Angstroms 10^-10 meter) with precise control of thickness, and it has the potential to meet the requirements for scaling challenges.

In the Strandwitz lab in Lehigh University’s Materials Science Department, we use ALD for depositing materials for the above mentioned and various other applications.¹ You can check our website for more details about our research and listen to this podcast episode by our principle investigator, Dr. Nick Strandwitz, to know more about ALD.

What is ALD? 

Atomic layer deposition (ALD) is a process used to create highly uniform surface coatings that are only a few atoms thick (0.1-1 nm). The ALD process consists of two chemical vapor dosing and purging steps, forming one cycle. These steps are self-limiting half cycles, where chemical precursor vapors are used to deposit a single atomic layer of the desired material thickness. This self-limiting reaction ensures that the available surface sites become saturated, preventing additional reactions. Each cycle deposits a single atomic layer onto the substrate and by repeating the cycles, a material with desired thickness can be grown.

(Figure source: www.atomiclimits.com)

Atomic Layer Deposition (ALD) enables the deposition of a diverse range of materials, including metals, metal oxides, sulphides, and nitrides, catering to various applications across different surfaces. The growth process is influenced by crucial parameters such as deposition temperature and reactant exposure times. To facilitate the reaction between chemical precursors and the surface, it is necessary to surpass an energy barrier, which is achieved by elevating the deposition temperature. Consequently, adjusting the deposition temperature in ALD allows for modifying the material thickness deposited after each cycle.

Surfaces with intricate geometries, like pores or deep trenches, pose a challenge as the chemical vapors take longer to diffuse through these features, leading to uneven growth. Hence, such complex surfaces demand a longer exposure time when compared to smoother surfaces, which require less exposure time. Thus, both growth temperature and reactant exposure times significantly impact the ALD growth of materials.

Cross-sectional image of 60 nm thick (greyish white coating on the trenches) conformal germanium antimony telluride (Ge₂Sb₂Te₅) ALD film on 600 nm trenches observed using scanning electron microscope.²

The power of miniaturization continues to drive astonishing advancements in our technology-driven world. Integrated circuits and their components have transformed our devices, making them faster, more efficient, and smaller than ever before. ALD provides a precise and controlled means of depositing materials at the atomic level. As we explore the possibilities of ALD, we unlock new opportunities in electronics, solar energy, and protective coatings. By understanding and optimizing influential parameters like temperature, time, and other factors, we can shape the future of material growth and drive even more remarkable innovations. The journey of miniaturization, combined with ALD, promises a world of limitless possibilities.

References:

(1) Vemuri, V.; King, S. W.; Lanford, W. A.; Gaskins, J. T.; Hopkins, P. E.; Van Derslice, J.; Li, H.; Strandwitz, N. C. Comprehensive Study of the Chemical, Physical, and Structural Evolution of Molecular Layer Deposited Alucone Films during Thermal Processing. Chem. Mater. 2023, 35 (5), 1916–1925.

(2) Pore, V.; Hatanpää, T.; Ritala, M.; Leskela, M. Atomic Layer Deposition of Metal Tellurides and Selenides Using Alkylsilyl Compounds of Tellurium and Selenium. J. Am. Chem. Soc. 2009, 131 (10), 3478–3480.