The scientific and technological interest in atomic layer deposition (ALD) and atomic layer etching (ALE) has been surging in the last decade and the sheer volume of ALD and ALE papers can make it difficult to get a clear overview of what is going on. Luckily, the studies and trends are often summarized and compared in review papers. Our blogpost in 2019 about our latest review on plasma ALD also included a comprehensive overview of ALD review papers. However now we have taken it one step further: we have tabulated the ALD and ALE review papers to date in a ReviewBase that is accessible directly from our blog. Just click the link in the header of this webpage. In this post we highlight some trends and conclusions that can be drawn from the ALD and ALE ReviewBase.
Since our blogpost in 2019, the number of ALD review papers has increased by 50%, which is quite astonishing and underlines the popularity of the method. However in the recent years, ALE has been gaining traction too. In 2015 several ALE review papers appeared, most as part of a focus issue in the ECS Journal of Solid State Science and Technology on Atomic Layer Etching and Cleaning. Furthermore, in the same year the seminal review “Overview of atomic layer etching in the semiconductor industry” by Keren Kanarik appeared in the Journal of Vacuum Science and Technology A.
The aforementioned ReviewBase can be used to browse all the review papers in the field of ALD and ALE. One can sort by author, year, journal and more. The most popular review papers can be identified at a glance. One can spot some interesting trends and fun facts from this ReviewBase: changes in popularity, the rate of growth in citations, emerging topics, and rising stars. We comment on these below.
Before doing that, let’s first briefly describe how we put this ReviewBase together.
Input for ALD & ALE ReviewBase and how you can contribute
To generate the ReviewBase for ALD and ALE we used Web-of-Science. As search terms we simply used “Atomic Layer Deposition” or “Atomic Layer Etching” and as “document type” we choose “review”. We also added some publications manually. Here two aspects are important to consider. First of all, it is sometimes a grey area what is exactly a review paper and what not. Note that not all reviews are listed as such in Web-of-Science. So here we used our own judgement. Secondly, there are certainly some reviews missing in the list. This holds for example for older ones on ALD (think about papers when the method was still known as “Atomic Layer Epitaxy”, see post about history of ALD). We plan to add these and other reviews manually over time. However, very importantly, you can also notify us about missing review papers by leaving a comment or by sending us a message. We are happy to add those after verifying the review nature of the publication.
Top 6 ALD review papers
The number of citations per year of the top 6 most cited ALD review papers is shown in the figure above. We picked the first 6 because these cover general ALD, while more specific applications are covered by papers lower in the list. The graph is not cumulative, instead it shows the increase in citations per year. The top 6 does not appear to have shifted much since our last blogpost about the review papers. The George 2010 paper—“Atomic Layer Deposition: An Overview”—is clearly the most popular still, and the growth of all of the papers except for the Johnson 2013 paper—“A brief review of atomic layer deposition: from fundamentals to applications”—appears to be steady. The paper by Johnson et al. stands out: its citations per year count has increased dramatically, perhaps it is related to its open access nature. While growth may appear to have levelled in recent years, the total amount of review papers and citations keeps increasing, leading to greater-than-linear growth for the collective review papers.
Top 5 ALE review papers
Analogous to the graph of the ALD reviews, the most popular ALE review papers show steady growth as well. We show the first 5, which cover general ALE. The main exception to steady growth is the George 2020 review paper—focusing on general ALE—which obviously has gained traction. Thermal ALE is a relatively new development, essentially catering to an entire new ALE subfield.
Emerging trends in ALD
The top 20 ALD review papers are shown in the table at the end of this blog post. From this table, we can identify a few trends. Because the diversity in ALE papers is not yet broad enough, this analysis is only performed on the ALD review papers.
The success of the top 6 has been explained already, but other trends can be subdivided among several topics. Important to note is that approximately half of all ALD reviews specifically focus on applications of ALD, where the paper of Knez 2007 is a highly-cited example, covering the manufacture of nanostructures using ALD. Other applications of ALD are catalysis in the papers of O’Neil 2015 and Lu 2013, Li-ion batteries by Meng 2012, using ALD to coat porous materials by Detavernier 2011, and energy and environment by Marichy 2012. Approximately half of application-focused ALD reviews cover energy applications, including solar cells, batteries, (photo-/electro-)catalysis, and fuel cells. One explanation for the surge in energy applications may be the push for energy-efficient devices.
A second category for ALD review papers is ALD techniques. Three papers stand out, namely a paper on plasma-enhanced ALD (PEALD) by Profijt 2011, a spatial ALD review paper by Poodt 2012, and area-selective ALD by Mackus 2014. The field of ALD is mature enough to spawn subfields detailing new applications. The three ALD variants show that ALD comes in more and more ‘flavors’.
Materials that have shown up in the review papers are metals and nitrides in the paper of Kim 2003, ZnO in the paper of Tynell 2014, and noble metals in the paper of Hämäläinen 2014. Nearly 1 in 4 of all ALD reviews covers specific materials, such as TiO2, ZnO, and the budding field of 2D materials.
Lastly, Langereis 2011 detailed the use of in-situ ellipsometry to characterize ALD, which is a relatively common method to track the growth per cycle nowadays.
ALD and ALE are both rapidly growing fields. The foundation (of the most popular review papers) is steady, indicating that the insights or explanations therein may still be relevant to new papers. Review papers about more specific applications show that the ALD field is large enough to show diverging applications, ranging from specific materials to the application methods themselves (see also our blog post about applications of ALD). The steady increase in citations indicates that the fields are not slowing down. As more niche applications for ALD and ALE are found, broader adoption is to be expected. New applications are still being found: ALD has been used in food packaging and medicine as well, and if the merits are clear, it will only be a matter of time before a review paper can be read about this.
The steady growth of the fields shows that as the smallest-scale manufacturing processes shrink more and more, the impact of ALD and ALE grows.
|George||Atomic Layer Deposition: An Overview||3717||Chem. Rev.||2010||●|
|Puurunen||Surface chemistry of atomic layer deposition: A case study for the trimethylaluminum/water process||1830||J. Appl. Phys.||2005||●|
|Miikkulainen et al.||Crystallinity of inorganic films grown by atomic layer deposition: Overview and general trends||956||J. Appl. Phys.||2013||▲|
|Leskelä et al.||Atomic Layer Deposition (ALD): from precursors to thin film structures||893||Thin Solid FIlms||2002||★|
|Johnson et al.||A brief review of atomic layer deposition: from fundamentals to applications||849||Mater. Today||2014||▲|
|Leskelä et al.||Atomic layer deposition chemistry: Recent developments and future challenges||814||Angew. Chem.-Int. Edit.||2003||▼|
|Knez et al.||Synthesis and surface engineering of complex nanostructures by atomic layer deposition||563||Adv. Mater.||2007||▼|
|Profijt et al.||Plasma-Assisted Atomic Layer Deposition: Basics, Opportunities, and Challenges||551||J. Vac. Sci. Technol. A||2011||●|
|Kim||Atomic layer deposition of metal and nitride thin films: Current research efforts and applications|
for semiconductor device processing
|480||J. Vac. Sci. Technol. B||2003||▼|
|Kim et al.||Applications of atomic layer deposition to nanofabrication and emerging nanodevices||447||Thin Solid Films||2009||▼|
|O’Neill et al.||Catalyst Design with Atomic Layer Deposition||422||ACS Catal.||2015||●|
|Meng et al.||Emerging Applications of Atomic Layer Deposition for Lithium-Ion Battery Studies||410||Adv. Mater.||2012||▼|
|Marichy et al||Atomic layer deposition of nanostructured materials for energy and environmental applications||409||Adv. Mater.||2012||★|
|Detavernier et al.||Tailoring nanoporous materials by atomic layer deposition||275||Chem. Soc. Rev.||2011||▼|
|Tynell et al.||Atomic layer deposition of ZnO: a review||256||Semicond. Sci. Technol.||2014||▼|
|Langereis et al.||In situ spectroscopic ellipsometry as a versatile tool for studying atomic layer deposition||227||J. Phys. D-Appl. Phys.||2009||▼|
|Hamalainen et al.||Atomic Layer Deposition of Noble Metals and Their Oxides||221||Chem. Mat.||2014||●|
|Mackus et al.||The use of atomic layer deposition in advanced nanopatterning||221||Nanoscale||2014||▲|
|Lu et al.||Synthesis and Stabilization of Supported Metal Catalysts by Atomic Layer Deposition||204||Accounts Chem. Res.||2013||▼|
|Poodt et al.||Spatial atomic layer deposition: A route towards further industrialization of atomic layer|
|194||J. Vac. Sci. Technol. A||2012||▼|
The full ALD and ALE reviews tables can be found here in excel and PDF form.
The ReviewBase has been put together by Joost Maas, Miika Mattinen, Harm Knoops, Bart Macco and Erwin Kessels. They will also take care of the content management and they all contributed to this blog post. The title figure was created with www.wordclouds.com using all the review titles from the ALD ReviewBase.