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Characterizing fluorocarbon assisted atomic layer etching of Si using cyclic Ar/C4F8 and Ar/CHF3 plasma
Dominik Metzler1, Chen Li2, Sebastian Engelmann3
1Department of Material Science and Engineering, and Institute for Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742, USA.
The Journal of Chemical Physics
|February 10, 2017
Summary
This study introduces a cyclic plasma process for atomic layer etching of silicon dioxide and silicon, optimizing material removal rates and selectivity through precise control of fluorocarbon precursors and ion bombardment.
Area of Science:
- Materials Science and Engineering
- Plasma Physics
- Surface Chemistry
Background:
- Fabricating highly scaled electronic devices requires directional etching with atomic scale resolution.
- Atomic layer etching (ALE) processes are crucial for achieving atomic layer precision in etching.
Purpose of the Study:
- To develop and characterize an Angstrom-level etching process for SiO2 and Si using a flux-controlled cyclic plasma method.
- To investigate the impact of process parameters on etch depth, removal rates, and selectivity.
Main Methods:
- Utilized a flux-controlled cyclic plasma process with steady-state Ar plasma, periodic fluorocarbon (FC) precursor injection (C4F8, CHF3), and synchronized Ar+ ion bombardment.
- Employed in situ real-time ellipsometry to examine etch depth per cycle, removal rates, and self-limitation.
- Used X-ray photoelectron spectroscopy (XPS) to analyze surface chemistry.
Main Results:
- The deposited FC thickness per cycle significantly impacts etch depth for SiO2 and Si, but has limited control over selectivity.
- Ion energy in the 20-30 eV range strongly influences material selectivity.
- CHF3 precursor shows lower FC deposition yield and greater substrate dependence compared to C4F8, with thicker FC layers on Si than SiO2.
Conclusions:
- The cyclic etching approach offers a large parameter space for process optimization, differing significantly from conventional steady-state etching.
- Precise control over FC deposition and ion energy is key to achieving desired etch characteristics.
- Surface chemistry dynamics within each cycle are crucial and depend on FC film thickness.
