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Etch mechanism of an Al₂O₃ hard mask in the Bosch process

  • The etching of high aspect ratio structures in silicon via the Bosch process is essential in modern technologies such as microelectromechanical systems (MEMS) and through‑silicon vias (TSV) fabrication. The process can be very demanding on the mask selectivity due to long etching times, and it has been shown that an Al2O3 hard mask is very suitable in this regard, as it offers significantly higher selectivity compared to the conventional SiO2 or resist masks. In this work, we employ a combination of Scanning Electron Microscopy (SEM), Spectroscopic Ellipsometry (SE) and X-Ray Photoelectron Spectroscopy (XPS) depth profiling to scrutinize the Al2O3 mask etching mechanism and therefore the origin of the extraordinary high selectivity. We demonstrate that by increasing the passivation step time, a thicker fluorocarbon polymer layer is formed on the Al2O3, and Al2O3 is then removed with a minuscule average etch rate of 0.01 nm/min. XPS depth profiling reveals that during Deep Reactive Ion Etching (DRIE) using the Bosch process, an AlFx layer is formed between the polymer and Al2O3. As AlFx is non-volatile, it requires sputtering to be removed. If the polymer layer is thick enough to attenuate the incoming ions such that their energy is not sufficient to lead to desorption of AlFx, such as when using a longer passivation time, the mask is not eroded. By investigating the surface after different amounts of DRIE cycles, we also obtained information about the formation rate of AlFx and the changes in the Al2O3 and polymer thicknesses over the course of a DRIE process. These findings further expand the knowledge of DRIE and can help process engineers to tailor the processes accordingly.

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Metadaten
Author:Martin Drost, Steffen Marschmeyer, Mirko Fraschke, Oksana Fursenko, Florian Bärwolf, Ioan Costina, Mamathamba Kalishettyhalli MahadevaiahORCiD, Marco LiskerORCiD
URN:urn:nbn:de:kobv:526-opus4-15678
DOI (Version of Record):https://doi.org/10.1016/j.mne.2021.100102
ISSN:2590-0072
Parent Title (English):Micro and Nano Engineering
Publisher:Elsevier
Document Type:Article
Language:English
Year of Publication:2022
Publishing Institution:Technische Hochschule Wildau
Release Date:2022/01/10
Tag:Bosch process; aluminum oxide; deep reactive ion etching
Volume:14
Article Number:100102
Source:Drost, M., Marschmeyer, D., Fraschke, M., Fursenko, O., Bärwolf, F., Costina, I., … Lisker, M. (2022). Etch mechanism of an Al2O3 hard mask in the Bosch process. Micro and Nano Engineering, 14, 100102. doi:10.1016/j.mne.2021.100102
Faculties an central facilities:Fachbereich Ingenieur- und Naturwissenschaften
Dewey Decimal Classification:6 Technik, Medizin, angewandte Wissenschaften / 62 Ingenieurwissenschaften / 620 Ingenieurwissenschaften und zugeordnete Tätigkeiten
Licence (German):Creative Commons - CC BY-NC-ND - Namensnennung - Nicht kommerziell - Keine Bearbeitungen 4.0 International
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