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Title: Etching of Si3N4 induced by electron beam plasma from hollow cathode plasma in a downstream reactive environment

Abstract

An etching system based on the interaction of electrons extracted from a direct current (DC) hollow-cathode (HC) Ar plasma and injected towards a Si3N4 covered silicon substrate located in the downstream reactive environment created by an additional remote CF4/O2 plasma source was developed and evaluated. By controlling the properties of the injected beam electrons, this approach allows to deliver energy to a surface functionalized by exposure to reactive species, and initiate surface etching. The energy of the primary beam electrons is controlled by the acceleration voltage relative to the HC discharge. Ar atoms flow from the high-pressure HC discharge into the low pressure downstream reactive environment in the process chamber. For an acceleration voltage greater than the ionization potential of Ar and/or process gas species, the energetic primary beam electrons produce a secondary plasma in the process chamber, and can also cause additional dissociation. We have characterized the properties of the secondary plasma and also surface etching of Si3N4 as a function of process parameters, including acceleration voltage (0-80 V), discharge current of the HC discharge (1-2 A), pressure (3.5-20 mTorr), source to substrate distance (1.5 to 5 cm), and feed gas composition (20% and 80% O2 in CF4/O2). Themore » electron energy probability function (EEPF) measured with a Langmuir probe about 2.5 cm below the extraction ring suggests several major groups of electrons for this situation, including high energy primary beam electrons with an energy that varies as the acceleration voltage is changed and low energy electrons produced by beam electron-induced ionization of the Ar gas in the process chamber. When a remote CF4/O2 plasma is additionally coupled to the process chamber, Si3N4 surfaces can be functionalized, and by varying the energy of the beam electrons, Si3N4 etching can be induced by electron-neutral synergy effect with plasma-surface interaction. For conditions without beam electron injection, the remote plasma etching rate (ER) of Si3N4 depends strongly on the O2 concentration in the CF4/O2 processing gas mixture and can be suppressed for O2-rich process conditions by the formation of a SiONF passivation layer on the Si3N4 surface. The combination of the HC electron beam source with the remote plasma source (HCEB-RP) makes it possible to induce Si3N4 etching for O2-rich remote plasma conditions where remote plasma by itself produces negligible Si3N4 etching. The electron enhanced etching of Si3N4 depends strongly on O2/CF4 mixing ratio reflecting changing arrival rates of O and F species at the surface. Optical emission spectroscopy was used to estimate the ratio of gas phase F and O densities and found to be controlled by the gas mixing ratio and independent of HC EB operating conditions. At this time the detailed sequence of events operative in the etching mechanism is unclear. While the increase of the electron energy is ultimately responsible for initiating surface etching, at present we cannot rule out a role of ions from the simultaneously produced secondary plasma in plasma surface interaction mechanisms.« less

Authors:
ORCiD logo [1];  [2];  [2]; ORCiD logo [3]; ORCiD logo [1]
  1. Univ. of Maryland, College Park, MD (United States)
  2. Carl Zeiss SMS GmbH, Rossdorf (Germany)
  3. Univ. of Michigan, Ann Arbor, MI (United States); RF Plasma Consulting, Brookline, MA (United States)
Publication Date:
Research Org.:
Univ. of Maryland, College Park, MD (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES)
OSTI Identifier:
1779715
Alternate Identifier(s):
OSTI ID: 1632905
Grant/Contract Number:  
SC0001939
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Vacuum Science and Technology B
Additional Journal Information:
Journal Volume: 38; Journal Issue: 3; Journal ID: ISSN 2166-2746
Publisher:
American Vacuum Society / AIP
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; plasma; etching; surface; electron beam

Citation Formats

Li, Chen, Hofmann, Thorsten, Edinger, Klaus, Godyak, Valery, and Oehrlein, Gottlieb S. Etching of Si3N4 induced by electron beam plasma from hollow cathode plasma in a downstream reactive environment. United States: N. p., 2020. Web. doi:10.1116/1.5143538.
Li, Chen, Hofmann, Thorsten, Edinger, Klaus, Godyak, Valery, & Oehrlein, Gottlieb S. Etching of Si3N4 induced by electron beam plasma from hollow cathode plasma in a downstream reactive environment. United States. https://doi.org/10.1116/1.5143538
Li, Chen, Hofmann, Thorsten, Edinger, Klaus, Godyak, Valery, and Oehrlein, Gottlieb S. Thu . "Etching of Si3N4 induced by electron beam plasma from hollow cathode plasma in a downstream reactive environment". United States. https://doi.org/10.1116/1.5143538. https://www.osti.gov/servlets/purl/1779715.
@article{osti_1779715,
title = {Etching of Si3N4 induced by electron beam plasma from hollow cathode plasma in a downstream reactive environment},
author = {Li, Chen and Hofmann, Thorsten and Edinger, Klaus and Godyak, Valery and Oehrlein, Gottlieb S.},
abstractNote = {An etching system based on the interaction of electrons extracted from a direct current (DC) hollow-cathode (HC) Ar plasma and injected towards a Si3N4 covered silicon substrate located in the downstream reactive environment created by an additional remote CF4/O2 plasma source was developed and evaluated. By controlling the properties of the injected beam electrons, this approach allows to deliver energy to a surface functionalized by exposure to reactive species, and initiate surface etching. The energy of the primary beam electrons is controlled by the acceleration voltage relative to the HC discharge. Ar atoms flow from the high-pressure HC discharge into the low pressure downstream reactive environment in the process chamber. For an acceleration voltage greater than the ionization potential of Ar and/or process gas species, the energetic primary beam electrons produce a secondary plasma in the process chamber, and can also cause additional dissociation. We have characterized the properties of the secondary plasma and also surface etching of Si3N4 as a function of process parameters, including acceleration voltage (0-80 V), discharge current of the HC discharge (1-2 A), pressure (3.5-20 mTorr), source to substrate distance (1.5 to 5 cm), and feed gas composition (20% and 80% O2 in CF4/O2). The electron energy probability function (EEPF) measured with a Langmuir probe about 2.5 cm below the extraction ring suggests several major groups of electrons for this situation, including high energy primary beam electrons with an energy that varies as the acceleration voltage is changed and low energy electrons produced by beam electron-induced ionization of the Ar gas in the process chamber. When a remote CF4/O2 plasma is additionally coupled to the process chamber, Si3N4 surfaces can be functionalized, and by varying the energy of the beam electrons, Si3N4 etching can be induced by electron-neutral synergy effect with plasma-surface interaction. For conditions without beam electron injection, the remote plasma etching rate (ER) of Si3N4 depends strongly on the O2 concentration in the CF4/O2 processing gas mixture and can be suppressed for O2-rich process conditions by the formation of a SiONF passivation layer on the Si3N4 surface. The combination of the HC electron beam source with the remote plasma source (HCEB-RP) makes it possible to induce Si3N4 etching for O2-rich remote plasma conditions where remote plasma by itself produces negligible Si3N4 etching. The electron enhanced etching of Si3N4 depends strongly on O2/CF4 mixing ratio reflecting changing arrival rates of O and F species at the surface. Optical emission spectroscopy was used to estimate the ratio of gas phase F and O densities and found to be controlled by the gas mixing ratio and independent of HC EB operating conditions. At this time the detailed sequence of events operative in the etching mechanism is unclear. While the increase of the electron energy is ultimately responsible for initiating surface etching, at present we cannot rule out a role of ions from the simultaneously produced secondary plasma in plasma surface interaction mechanisms.},
doi = {10.1116/1.5143538},
journal = {Journal of Vacuum Science and Technology B},
number = 3,
volume = 38,
place = {United States},
year = {2020},
month = {4}
}

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