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Unraveling the Mechanism of Maskless Nanopatterning of Black Silicon by CF(4)/H(2) Plasma Reactive-Ion Etching

[Image: see text] The process of deep texturization of the crystalline silicon surface is intimately related to its promising diverse applications, such as bactericidal surfaces for integrated lab-on-chip devices and absorptive optical layers (black silicon—BSi). Surface structuring by a maskless te...

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Autores principales: Ghezzi, Francesco, Pedroni, Matteo, Kovač, Janez, Causa, Federica, Cremona, Anna, Anderle, Mariano, Caniello, Roberto, Pietralunga, Silvia M., Vassallo, Espedito
Formato: Online Artículo Texto
Lenguaje:English
Publicado: American Chemical Society 2022
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9330092/
https://www.ncbi.nlm.nih.gov/pubmed/35910127
http://dx.doi.org/10.1021/acsomega.2c02740
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author Ghezzi, Francesco
Pedroni, Matteo
Kovač, Janez
Causa, Federica
Cremona, Anna
Anderle, Mariano
Caniello, Roberto
Pietralunga, Silvia M.
Vassallo, Espedito
author_facet Ghezzi, Francesco
Pedroni, Matteo
Kovač, Janez
Causa, Federica
Cremona, Anna
Anderle, Mariano
Caniello, Roberto
Pietralunga, Silvia M.
Vassallo, Espedito
author_sort Ghezzi, Francesco
collection PubMed
description [Image: see text] The process of deep texturization of the crystalline silicon surface is intimately related to its promising diverse applications, such as bactericidal surfaces for integrated lab-on-chip devices and absorptive optical layers (black silicon—BSi). Surface structuring by a maskless texturization appeals as a cost-effective approach, which is up-scalable for large-area production. In the case of silicon, it occurs by means of reactive plasma processes (RIE—reactive-ion etching) using fluorocarbon CF(4) and H(2) as reaction gases, leading to self-assembled cylindrical and pyramidal nanopillars. The mechanism of silicon erosion has been widely studied and described as it is for the masked RIE process. However, the onset of the erosion and the reaction kinetics leading to defined maskless patterning have not been unraveled to date. In this work, we specifically tackle this issue by analyzing the results of three different RIE recipes, specifically designed for the purpose. The mechanism of surface self-nanopatterning is revealed by deeply investigating the physical chemistry of the etching process at the nanoscale and the evolution of surface morphology. We monitored the progress in surface patterning and the composition of the etching plasma at different times during the RIE process. We confirm that nanopattering issues from a net erosion, as contributed by chemical etching, physical sputtering, and by the synergistic plasma effect. We propose a qualitative model to explain the onset, the evolution, and the stopping of the process. As the RIE process is started, a high density of surface defects is initially created at the free silicon surface by energetic ion sputtering. Contextually, a polymeric overlayer is synthesized on the Si surface, as thick as 5 nm on average, and self-aggregates into nanoclusters. The latter phenomenon can be explained by considering that the initial creation of surface defects increases the activation energy for surface diffusion of deposited CF and CF(2) species and prevents them from aggregating into a continuous Volmer–Weber polymeric film. The clusterization of the polymer provides the self-masking effect since the beginning, which eventually triggers surface patterning. Once started, the maskless texturing proceeds in analogy with the masked case, that is, by combined chemical etching and ion sputtering, and ceases because of the loss of ion energy. In the case of CF(4)/H(2) RIE processes at 10% of H(2) and by supplying 200 W of RF power for 20 min, nanopillars of 200 nm in height and 100 nm in width were formed. We therefore propose that a precise assessment of surface defect formation and density in dependence on the initial RIE process parameters can be the key to open a full control of outcomes of maskless patterning.
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spelling pubmed-93300922022-07-29 Unraveling the Mechanism of Maskless Nanopatterning of Black Silicon by CF(4)/H(2) Plasma Reactive-Ion Etching Ghezzi, Francesco Pedroni, Matteo Kovač, Janez Causa, Federica Cremona, Anna Anderle, Mariano Caniello, Roberto Pietralunga, Silvia M. Vassallo, Espedito ACS Omega [Image: see text] The process of deep texturization of the crystalline silicon surface is intimately related to its promising diverse applications, such as bactericidal surfaces for integrated lab-on-chip devices and absorptive optical layers (black silicon—BSi). Surface structuring by a maskless texturization appeals as a cost-effective approach, which is up-scalable for large-area production. In the case of silicon, it occurs by means of reactive plasma processes (RIE—reactive-ion etching) using fluorocarbon CF(4) and H(2) as reaction gases, leading to self-assembled cylindrical and pyramidal nanopillars. The mechanism of silicon erosion has been widely studied and described as it is for the masked RIE process. However, the onset of the erosion and the reaction kinetics leading to defined maskless patterning have not been unraveled to date. In this work, we specifically tackle this issue by analyzing the results of three different RIE recipes, specifically designed for the purpose. The mechanism of surface self-nanopatterning is revealed by deeply investigating the physical chemistry of the etching process at the nanoscale and the evolution of surface morphology. We monitored the progress in surface patterning and the composition of the etching plasma at different times during the RIE process. We confirm that nanopattering issues from a net erosion, as contributed by chemical etching, physical sputtering, and by the synergistic plasma effect. We propose a qualitative model to explain the onset, the evolution, and the stopping of the process. As the RIE process is started, a high density of surface defects is initially created at the free silicon surface by energetic ion sputtering. Contextually, a polymeric overlayer is synthesized on the Si surface, as thick as 5 nm on average, and self-aggregates into nanoclusters. The latter phenomenon can be explained by considering that the initial creation of surface defects increases the activation energy for surface diffusion of deposited CF and CF(2) species and prevents them from aggregating into a continuous Volmer–Weber polymeric film. The clusterization of the polymer provides the self-masking effect since the beginning, which eventually triggers surface patterning. Once started, the maskless texturing proceeds in analogy with the masked case, that is, by combined chemical etching and ion sputtering, and ceases because of the loss of ion energy. In the case of CF(4)/H(2) RIE processes at 10% of H(2) and by supplying 200 W of RF power for 20 min, nanopillars of 200 nm in height and 100 nm in width were formed. We therefore propose that a precise assessment of surface defect formation and density in dependence on the initial RIE process parameters can be the key to open a full control of outcomes of maskless patterning. American Chemical Society 2022-07-11 /pmc/articles/PMC9330092/ /pubmed/35910127 http://dx.doi.org/10.1021/acsomega.2c02740 Text en © 2022 The Authors. Published by American Chemical Society https://creativecommons.org/licenses/by-nc-nd/4.0/Permits non-commercial access and re-use, provided that author attribution and integrity are maintained; but does not permit creation of adaptations or other derivative works (https://creativecommons.org/licenses/by-nc-nd/4.0/).
spellingShingle Ghezzi, Francesco
Pedroni, Matteo
Kovač, Janez
Causa, Federica
Cremona, Anna
Anderle, Mariano
Caniello, Roberto
Pietralunga, Silvia M.
Vassallo, Espedito
Unraveling the Mechanism of Maskless Nanopatterning of Black Silicon by CF(4)/H(2) Plasma Reactive-Ion Etching
title Unraveling the Mechanism of Maskless Nanopatterning of Black Silicon by CF(4)/H(2) Plasma Reactive-Ion Etching
title_full Unraveling the Mechanism of Maskless Nanopatterning of Black Silicon by CF(4)/H(2) Plasma Reactive-Ion Etching
title_fullStr Unraveling the Mechanism of Maskless Nanopatterning of Black Silicon by CF(4)/H(2) Plasma Reactive-Ion Etching
title_full_unstemmed Unraveling the Mechanism of Maskless Nanopatterning of Black Silicon by CF(4)/H(2) Plasma Reactive-Ion Etching
title_short Unraveling the Mechanism of Maskless Nanopatterning of Black Silicon by CF(4)/H(2) Plasma Reactive-Ion Etching
title_sort unraveling the mechanism of maskless nanopatterning of black silicon by cf(4)/h(2) plasma reactive-ion etching
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9330092/
https://www.ncbi.nlm.nih.gov/pubmed/35910127
http://dx.doi.org/10.1021/acsomega.2c02740
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