69th Annual Gaseous Electronics Conference
Volume 61, Number 9
Monday–Friday, October 10–14, 2016;
Bochum, Germany
Session JW2: Capacitively Coupled Plasmas II
8:30 AM–10:00 AM,
Wednesday, October 12, 2016
Room: 2a
Chair: Shahid Rauf, Applied Materials, Inc
Abstract ID: BAPS.2016.GEC.JW2.1
Abstract: JW2.00001 : Experimental and simulation study of capacitively coupled electronegative discharges
8:30 AM–9:00 AM
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Abstract
Author:
Aranka Derzsi
(Wigner Research Centre for Physics, Budapest, Hungary)
The application of tailored voltage waveforms, generated by using multiple
harmonics of a base frequency, for the excitation of capacitive RF
discharges has been recently introduced as a new method to control the ion
flux and ion energy distribution at the electrodes. In plasma processing of
surfaces complex mixtures of electronegative, reactive gases (e.g.
CF$_{\mathrm{4}}$, O$_{\mathrm{2}})$ are usually required. Therefore, the
question of whether this new approach to control ion properties can be
applied efficiently to such systems is of exceptional importance.
Here the electron heating and ionization dynamics, the possibilities and
limitations of the efficient control of plasma parameters by voltage
waveform tailoring in low-pressure capacitively coupled electronegative
discharges are presented. The focus is on geometrically symmetric
O$_{\mathrm{2}}$ plasmas, which are investigated by PIC/MCC simulations and
experimental methods. O$_{\mathrm{2}}$ discharges driven by impulse-type and
sawtooth-type voltage waveforms composed of a maximum of four consecutive
harmonics are studied. Experimental results on the dc self-bias voltage, as
well as the spatiotemporal distribution of the plasma emission are compared
with simulation data for a wide range of operating conditions (fundamental
driving frequencies of 5 MHz -- 15 MHz, at pressures of 50 mTorr -- 700
mTorr). Transitions between electron power absorption due to sheath
expansion and the drift-ambipolar mode were induced both by changing the
number of harmonics or by changing the gas pressure. A good agreement
between simulation and experiment is found, which shows that the
collision-reaction model for O$_{\mathrm{2}}$ discharges underlying the
simulations describes reasonably the complicated chemistry of oxygen
plasmas. An investigation of the dependence of the discharge characteristics
on the surface destruction coefficient of the
O$_{\mathrm{2}}$(a$^{\mathrm{1}}\Delta_{\mathrm{g}})$ singlet
metastable molecules revealed the crucial role of these species, which
strongly affects the negative ion balance of the plasma.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2016.GEC.JW2.1