Low-Energy Plasma Source for Clean Vacuum Environments: EUV Lithography and Optical Mirrors Cleaning

Plasma cleaning of extreme ultra-violet (EUV) optics for the semiconductor industry requires atomic-level precision. Low-energy ions and neutrals can be highly beneficial for this purpose. However, ion energies in many industrial capacitively or inductively coupled plasmas may be too high for atomic...

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Bibliographic Details
Published in:IEEE transactions on plasma science 2021-10, Vol.49 (10), p.3132-3141
Main Authors: van Veldhoven, Jacqueline, Stodolna, Aneta S., Storm, Arnold, van den Brink, Jeroen, Geerits, Niels, Vlaar, Jasper, Dekker, Michael, Ushakov, Andrey
Format: Article
Language:English
Subjects:
Accelerated tests
Clean energy
Cleaning
Contamination
Electrodes
Electron beams
Energy
gas discharge devices
Gas ionization
Inductively coupled plasma
Ion impact
Ionization
Ions
Lithography
low-temperature plasmas
Mirrors
nuclear and plasma sciences
Optics
Plasma
plasma applications
plasma devices
plasma materials processing
plasma properties
Plasmas
Plasmas (physics)
Radio frequency
Ultraviolet sources
X ray photoelectron spectroscopy
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Summary:Plasma cleaning of extreme ultra-violet (EUV) optics for the semiconductor industry requires atomic-level precision. Low-energy ions and neutrals can be highly beneficial for this purpose. However, ion energies in many industrial capacitively or inductively coupled plasmas may be too high for atomic precision processing so that ions can cause sputtering and re-deposition of materials and produce vacuum system contamination. We discuss two sources that create low-energy ions: a capacitively coupled (CCP) plasma source operating at several tens of MHz and an electron beam gas ionization source. The goal here is to minimize the contamination by limiting the ion impact energy to a few tens of electron-volts. Ion energy and flux measurements on a grounded surface are characterized with a compact retarding field ion spectrometer. Plasma-induced contamination is quantified using X-ray photo-electron spectroscopy (XPS). Low ion energy plasma sources introducing little surface contamination may be interesting for cleaning and accelerated testing in EUV lithography (EUVL)-related research and for cleaning of front-end optical mirrors in fusion reactor diagnostics.
ISSN:0093-3813
1939-9375
DOI:10.1109/TPS.2021.3110423