Saturday, February 8, 2020

Consistency and reproducibility in atomic layer deposition

ALD is usually sold as a straight forward thin film deposition technique wit excellent film thickness university and straight forward thickness scaling by the number of ALD cycles applied. Here us a recently published paper in JVSTA from the leading ALD researchers at Argonne National Laboratory discussing the process result variation from processes used reported by the same precursor from equipment in different labs showing a rather significant variation. 

(As shared on LinkeIn, JVSTA Editors pick LINK)

Consistency and reproducibility in atomic layer deposition

Henrik H. S√łnsteby, Angel Yanguas-Gil, and Jeffrey W. Elam
Journal of Vacuum Science & Technology A 38, 020804 (2020); https://doi.org/10.1116/1.5140603

Atomic layer deposition (ALD) is a thin film synthesis technique that can provide exquisite accuracy and precision in film thickness and composition even on complex, large area substrates. Based on self-limiting surface chemistry, ALD can be insensitive to process conditions and reactor designs, allowing an ALD process developed in one lab to be easily reproduced in other labs. In practice, however, ALD is sometimes difficult to reproduce or replicate, and the results can vary substantially between ALD reactors and between labs. This is exemplified by large deviations in reports on the growth of, e.g., Al2O3, FeOx, and TiO2 given the same precursors under similar conditions. Furthermore, the problem of irreproducibility seems to be growing as ALD is adopted by more researchers and integrated into new applications. In this article, the authors highlight some of the major sources of variations and errors and common misconceptions related to ALD. In particular, the authors focus on issues related to precursors, substrates, and deposition tools. The authors illustrate these problems through examples from the literature, and they present results from numerical simulations that describe how nonidealities would manifest in thickness profiles in a typical cross-flow reactor. They also describe how reproducibility in ALD is linked to consistent experimental practice and reporting between labs. The authors’ hope is that by educating newcomers to ALD and advocating for consistent reporting of deposition conditions, they can minimize irreproducibility and enable ALD practitioners to realize the full potential afforded by self-limiting surface chemistry

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