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:

Li, Chen  ^[1];

• Search DOE PAGES for author "Li, Chen"
• Search DOE PAGES for ORCID "0000-0003-2801-110X"

Hofmann, Thorsten ^[2]; Edinger, Klaus ^[2]; Godyak, Valery  ^[3];

• Search DOE PAGES for author "Godyak, Valery"
• Search DOE PAGES for ORCID "0000-0001-8611-0005"

Oehrlein, Gottlieb S.  ^[1]

• Search DOE PAGES for author "Oehrlein, Gottlieb S."
• Search DOE PAGES for ORCID "0000-0002-6693-4274"

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+ Show Author Affiliations

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:

Thu Apr 09 00:00:00 EDT 2020

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