Note: a list of ALD review papers is available at the end.
Atomic layer deposition or ALD is amazingly popular these days and this is also reflected by the large number of review articles that have appeared over the recent years. The latter will be illustrated by an overview at the end of this blog, but first I want to draw the attention to a new review article from our side that has just been published online. Its title is “Status and prospects of plasma-assisted atomic layer deposition” and the authors are Harm Knoops, Tahsin Faraz, Karsten Arts and Erwin Kessels. It has been published in Journal of Vacuum Science and Technology A, open access, as part of the special issue on Atomic layer deposition. It forms basically an update of the review article “Plasma-Assisted Atomic Layer Deposition: Basics, Opportunities, and Challenges” by Harald Profijt, Stephen Potts, Richard van de Sanden and Erwin Kessels that appeared in the same Journal of Vacuum Science and Technology A in 2011. The new review article gives an update what has happened in the field of plasma-assisted ALD (or plasma-enhanced ALD) in the last 8 years. And many things have happened! In short, the new review discusses the breakthrough of plasma-assisted ALD in manufacturing, the large number of processes and reactor designs now available, open fundamental research questions and the place of plasma-assisted ALD in the atomic-scale processing toolbox. Some selected highlights are discussed below.
Self-aligned double patterning (SADP) has become really indispensable in the toolbox for making small features and with it plasma ALD has entered the high-volume manufacturing stage already quite some years ago. A key requirement for SADP is conformal deposition of the spacer material (typically SiO2) to have accurate sidewall thicknesses which are needed for accurate reproduction of the desired pattern. Thermal ALD of SiO2 is challenging and generally requires high temperatures, while plasma ALD of SiO2 is a relatively facile and quick process. Interestingly, the use of ALD for self-aligned patterning has become the biggest of all the individual ALD markets and has resulted in a recurring upward adjustment of the predicted market size of ALD equipment for the future; here the main process used is plasma ALD of SiO2. Besides the use of plasma ALD for SADP, its use for self-aligned quadruple patterning (SAQP) has been demonstrated and with its importance for the (sub-)10 nm node it is clear that the use of plasma ALD for high-volume manufacturing stretches beyond plasma ALD of SiO2 for SADP.
Actual and forecasted ALD semiconductor equipment market size over the years. The adjustment of the most recent predictions to higher values is related to the emergence of applications such as self-aligned patterning employing plasma ALD (courtesy of Dr. I. Raaijmakers (ASM), data sources Gartner and ASM).
Besides large strides that have been made in plasma processing, there are also subjects in which deeper insights and successes have been obtained, but which remain challenging both from a scientific and technological vantage point. Plasma ALD is typically performed with a wide range of different plasma species present near the surface. But the variety of species present makes it very complex to predict what happens in the ALD process and what needs to be done to optimize or improve the process. Measuring and observing the plasma is key in understanding the processes taking place and knowing which species are present. An advantage of plasmas is that the light emitted by them gives direct information. Looking at the type of emission and the location of emission can be very instructive in understanding and postulation of hypotheses.
A range of plasmas as observed through a window on the side of a homebuilt inductively-coupled plasma system at the Eindhoven University of Technology. The color and brightness of the light even by eye give an indication of the species present. The chamber pressure was 0.016 mbar and the plasma power was 100 W.
By studying plasma emission and measuring various other plasma parameters and released species, a much better picture of the relevant processes has been obtained. These relate for instance to the role of energetic ions and background species and are discussed in separate sections, namely: plasma-surface interaction, ALD of metals and compounds that easily oxidize, plasma ALD on sensitive surfaces, conformal deposition, and low-temperature deposition. Together the main processes can be illustrated as below to give a general overview.
Schematic to illustrate species and processes important in plasma ALD. Plasma species generated from the feedstock gas interact with the surface, lead to film deposition, and affect film composition, structure, and defect levels. Reaction products formed on substrate and wall surfaces can dissociate in the plasma, redeposit and get incorporated in the film being prepared. Reactor aspects such as the gases used, background species, and pumping speed all have to be considered in possible processes during plasma ALD.
Besides discussions on what has been done and what are scientific and technological challenges, the review also discusses new and emerging developments. Based on our expectation and observations these are centered on the following topics: Area-selective ALD, 2D transition metal dichalcogenides, Molecular Layer Deposition, Plasma ALD and etching, and Scale up to large areas.
We are not the only ones trying to make sense of the field of ALD and subfields within and there have been many ALD related review papers. To illustrate this we used Web of Science to search for ALD related review papers. We found that the search terms TITLE: (“atomic layer deposition”) combined with DOCUMENT TYPES: (Review) gave the most representative list although we are sure there might be ones missing or certain ones on there that don’t fully fit our expectation of what an ALD review would be.
For those without access to Web of Science the list of reviews can be downloaded below:
- Excel file – Review articles sorted by publication year
- PDF file – Review articles sorted by publication year (for easy printing)
From this list we have selected the top 20 most cited ALD review articles below and I am sure that many of you recognize iconic papers in there that you have read. We are of course also happy that our previous plasma ALD review is in there as well. If we furthermore make a list of ALD review articles published in 2018 and 2019 (to date) as shown in the table at the end, we already notice that there are quite some papers so far. The number of review articles found is 9 for 2018 and already 8 for 2019!
Top 20 most cited ALD review articles returned by Web of Science on 15th of March 2019 sorted by number of citations. Search terms used were TITLE: (“atomic layer deposition”) combined with DOCUMENT TYPES: (Review).
|Author||Review article||Citations||Journal||Year published|
|George||Atomic Layer Deposition: An Overview||2403||Chem. Rev.||2010|
|Puurunen||Surface chemistry of atomic layer deposition: A case study for the trimethylaluminum/water process||1376||J. Appl. Phys.||2005|
|Leskela et al.||Atomic layer deposition chemistry: Recent developments and future challenges||640||Angew. Chem.-Int. Edit.||2003|
|Miikkulainen et al.||Crystallinity of inorganic films grown by atomic layer deposition: Overview and general trends||584||J. Appl. Phys.||2013|
|Knez et al.||Synthesis and surface engineering of complex nanostructures by atomic layer deposition||563||Adv. Mater.||2007|
|Kim||Atomic layer deposition of metal and nitride thin films: Current research efforts and applications
for semiconductor device processing
|395||J. Vac. Sci. Technol. B||2003|
|Kim et al.||Applications of atomic layer deposition to nanofabrication and emerging nanodevices||337||Thin Solid Films||2009|
|Profijt et al.||Plasma-Assisted Atomic Layer Deposition: Basics, Opportunities, and Challenges||331||J. Vac. Sci. Technol. A||2011|
|Johnson et al.||A brief review of atomic layer deposition: from fundamentals to applications||330||Mater. Today||2014|
|Meng et al.||Emerging Applications of Atomic Layer Deposition for Lithium-Ion Battery Studies||273||Adv. Mater.||2012|
|O’Neill et al.||Catalyst Design with Atomic Layer Deposition||192||ACS Catal.||2015|
|Detavernier et al.||Tailoring nanoporous materials by atomic layer deposition||181||Chem. Soc. Rev.||2011|
|Langereis et al.||In situ spectroscopic ellipsometry as a versatile tool for studying atomic layer deposition||147||J. Phys. D-Appl. Phys.||2009|
|Tynell et al.||Atomic layer deposition of ZnO: a review||130||Semicond. Sci. Technol.||2014|
|Poodt et al.||Spatial atomic layer deposition: A route towards further industrialization of atomic layer
|129||J. Vac. Sci. Technol. A||2012|
|Lu et al.||Synthesis and Stabilization of Supported Metal Catalysts by Atomic Layer Deposition||116||Accounts Chem. Res.||2013|
|Hamalainen et al.||Atomic Layer Deposition of Noble Metals and Their Oxides||112||Chem. Mat.||2014|
|Wang et al.||Controllable fabrication of nanostructured materials for photoelectrochemical water splitting via atomic
|111||Chem. Soc. Rev.||2014|
|Bakke et al.||Nanoengineering and interfacial engineering of photovoltaics by atomic layer deposition||109||Nanoscale||2011|
|Mackus et al.||The use of atomic layer deposition in advanced nanopatterning||97||Nanoscale||2014|
List of ALD review articles published in 2018 and 2019 (to date) returned by Web of Science on 15th of March 2019 (with our paper added at the end). Search terms used were TITLE: (“atomic layer deposition”) combined with DOCUMENT TYPES: (Review).
|Author||Review article||Journal||Year published|
|Cao et al.||Review Article: Catalysts design and synthesis via selective atomic layer deposition||J. Vac. Sci. Technol. A||2018|
|Weber et al.||Atomic Layer Deposition for Membranes: Basics, Challenges, and Opportunities||Chem. Mat.||2018|
|Onn et al.||Atomic Layer Deposition on Porous Materials: Problems with Conventional Approaches to Catalyst and Fuel Cell Electrode Preparation||Inorganics||2018|
|Yang et al.||Atomic layer deposition for membrane interface engineering||Nanoscale||2018|
|Adhikari et al.||Progress in Powder Coating Technology Using Atomic Layer Deposition||Adv. Mater. Interfaces||2018|
|Mantymaki et al.||Metal Fluorides as Lithium-Ion Battery Materials: An Atomic Layer Deposition Perspective||Coatings||2018|
|Hengwei et al.||Atomic Layer Deposition: A Gas Phase Route to Bottom-up Precise Synthesis of Heterogeneous Catalyst||Acta Phys.-Chim. Sin.||2018|
|Sheng et al.||Review Article: Atomic layer deposition for oxide semiconductor thin film transistors: Advances in research and development||J. Vac. Sci. Technol. A||2018|
|Zhang et al.||Interface Tailoring of Heterogeneous Catalysts by Atomic Layer Deposition||ACS Catal.||2018|
|Seo et al.||Atomic layer deposition for efficient and stable perovskite solar cells||Chem. Commun.||2019|
|Mackus et al.||Synthesis of Doped, Ternary, and Quaternary Materials by Atomic Layer Deposition: A Review||Chem. Mat.||2019|
|Prakash et al.||Emerging applications of atomic layer deposition for the rational design of novel nanostructures for surface-enhanced Raman scattering||J. Mater. Chem. C||2019|
|Weimer||Particle atomic layer deposition||J. Nanopart. Res.||2019|
|Hao et al.||Atomic layer deposition of stable 2D materials||2D Mater.||2019|
|Lee et al.||Review of Organic/Inorganic Thin Film Encapsulation by Atomic Layer Deposition for a Flexible OLED Display||JOM||2019|
|Subramanian et al.||Review of Recent Advances in Applications of Vapor-Phase Material Infiltration Based on Atomic Layer Deposition||JOM||2019|
|Knoops et al.||Status and prospects of plasma-assisted atomic layer deposition||J. Vac. Sci. Technol. A||2019|