Title: Characterizing Fluorocarbon Assisted Atomic Layer Etching of Si Using Cyclic Ar/C₄F₈ and Ar/CHF₃ Plasma

Abstract

With the increasing interest in establishing directional etching methods capable of atomic scale resolution for fabricating highly scaled electronic devices, the need for development and characterization of atomic layer etching (ALE) processes, or generally etch processes with atomic layer precision, is growing. In this work, a flux-controlled cyclic plasma process is used for etching of SiO₂ and Si at the Angstrom-level. This is based on steady-state Ar plasma, with periodic, precise injection of a fluorocarbon (FC) precursor (C₄F₈ and CHF₃), and synchronized, plasma-based Ar+ ion bombardment [D. Metzler et al., J Vac Sci Technol A 32, 020603 (2014), and D. Metzler et al., J Vac Sci Technol A 34, 01B101 (2016)]. For low energy Ar+ ion bombardment conditions, physical sputter rates are minimized, whereas material can be etched when FC reactants are present at the surface. This cyclic approach offers a large parameter space for process optimization. Etch depth per cycle, removal rates, and self-limitation of removal, along with material dependence of these aspects, were examined as a function of FC surface coverage, ion energy, and etch step length using in situ real time ellipsometry. The deposited FC thickness per cycle is found to have a strong impact on etchmore » depth per cycle of SiO₂ and Si, but is limited with regard to control over material etching selectivity. Ion energy over the 20 to 30 eV range strongly impacts material selectivity. The choice of precursor can have a significant impact on the surface chemistry and chemically enhanced etching. CHF₃ has a lower FC deposition yield for both SiO₂ and Si, and also exhibits a strong substrate dependence of FC deposition yield, in contrast to C4F₈. The thickness of deposited FC layers using CHF₃ is found to be greater for Si than for SiO₂. X-ray photoelectron spectroscopy was used to study surface chemistry. When thicker FC films of 11 Å are employed, strong changes of FC film chemistry during a cycle are seen whereas the chemical state of the substrate varies much less. On the other hand, for FC film deposition of 5 Å for each cycle, strong substrate surface chemical changes are seen during an etching cycle. The nature of this cyclic etching with periodic deposition of thin FC films differs significantly from conventional etching with steady-state FC layers since surface conditions change strongly throughout each cycle.« less

Authors:

Metzler, Dominik ^[1]; Li, Chen ^[2]; Engelmann, Sebastian ^[3]; Bruce, Robert L ^[3]; Joseph, Eric A ^[3]; Oehrlein, Gottlieb S ^[1]

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+ Show Author Affiliations

1. Univ. of Maryland, College Park, MD (United States). Inst. for Electronics and Applied Physics, Dept. of Material Science and Engineering
2. Univ. of Maryland, College Park, MD (United States). Inst. for Electronics and Applied Physics, Dept. of Physics
3. IBM, Yorktown Heights, NY (United States). Thomas J. Watson Research Center

Publication Date:

Thu Sep 08 00:00:00 EDT 2016

Research Org.:

Univ. of Maryland, College Park, MD (United States)

Sponsoring Org.:

USDOE; National Science Foundation (NSF)

OSTI Identifier:

1294595

Alternate Identifier(s):

OSTI ID: 1322428

Grant/Contract Number:  

SC0001939; CBET-1134273

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Chemical Physics

Additional Journal Information:

Journal Volume: 146; Journal Issue: 5; Journal ID: ISSN 0021-9606

Publisher:

American Institute of Physics (AIP)

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY