Experimental investigations of electron heating dynamics and ion energy distributions in capacitive discharges driven by customized voltage waveforms

Journal Article · Mon Dec 14 04:00:00 EST 2015 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.4937403· OSTI ID:22493018

Berger, Birk ^[1]; Brandt, Steven; Franek, James; Schüngel, Edmund; Koepke, Mark; Schulze, Julian ^[1]; Mussenbrock, Thomas ^[2]

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1. Department of Physics, West Virginia University, Morgantown, West Virginia 26506-6315 (United States)
2. Institute for Theoretical Electrical Engineering, Ruhr University Bochum, D-44780 Bochum (Germany)

Capacitively coupled radio frequency plasmas driven by customized voltage waveforms provide enhanced opportunities to control process-relevant energy distributions of different particle species. Here, we present an experimental investigation of the spatio-temporal electron heating dynamics probed by Phase-Resolved Optical Emission Spectroscopy (PROES) in an argon discharge driven by up to three consecutive harmonics of 13.56 MHz with individually adjustable harmonics' amplitudes and phases. PROES and voltage measurements are performed at fixed total voltage amplitudes as a function of the number of driving harmonics, their relative phases, and pressure to study the effects of changing the applied voltage waveform on the heating dynamics in collisionless and collisional regimes. Additionally, the ion energy distribution function (IEDF) is measured at low pressure. In this collisionless regime, the discharge is operated in the α-mode. The velocity of energetic electron beams generated by the expanding sheaths is found to be affected by the number of driving harmonics and their relative phases. This is understood based on the sheath dynamics obtained from a model that determines sheath voltage waveforms. The formation of the measured IEDFs is understood and found to be directly affected by the observed changes in the electron heating dynamics. It is demonstrated that the mean ion energy can be controlled by adjusting the harmonics' phases. In the collisional regime at higher pressures changing the number of harmonics and their phases at fixed voltage is found to induce heating mode transitions from the α- to the γ-mode. Finally, a method to use PROES as a non-invasive diagnostic to monitor and detect changes of the ion flux to the electrodes is developed.

• OSTI ID: 22493018
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 22 Vol. 118; ISSN JAPIAU; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
AMPLITUDES
ARGON
DISTRIBUTION FUNCTIONS
ELECTRIC POTENTIAL
ELECTRON BEAMS
EMISSION SPECTROSCOPY
ENERGY SPECTRA
HARMONICS
MHZ RANGE
PLASMA
PLASMA HEATING
PRESSURE RANGE KILO PA
PRESSURE RANGE MEGA PA 10-100
RADIOWAVE RADIATION
TAIL ELECTRONS
WAVE FORMS