Slope and amplitude asymmetry effects on low frequency capacitively coupled carbon tetrafluoride plasmas

Abstract

We report investigations of capacitively coupled carbon tetrafluoride (CF4) plasmas excited with tailored voltage waveforms containing up to five harmonics of a base frequency of 5.5 MHz. The impact of both the slope asymmetry, and the amplitude asymmetry, of these waveforms on the discharge is examined by combining experiments with particle-in-cell simulations. For all conditions studied herein, the discharge is shown to operate in the drift-ambipolar mode, where a comparatively large electric field in the plasma bulk (outside the sheaths) is the main mechanism for electron power absorption leading to ionization. We show that both types of waveform asymmetries strongly influence the ion energy at the electrodes, with the particularity of having the highest ion flux on the electrode where the lowest ion energy is observed. Even at the comparatively high pressure (600 mTorr) and low fundamental frequency of 5.5 MHz used here, tailoring the voltage waveforms is shown to efficiently create an asymmetry of both the ion energy and the ion flux in geometrically symmetric reactors

Controlling plasma properties under differing degrees of electronegativity using odd harmonic dual frequency excitation

“…Since the original study many investigations have demonstrated this effect through both simulation and experiment and extended it to the use of more than two frequencies to increase the amplitude asymmetry of the waveform [28][29][30][31][32][33][34][35][36][37][38][39][40][41]. It has also been demonstrated that an electrical asymmetry can be generated using sawtooth-like waveforms where the rise and fall times of the voltage waveform differ [41][42][43][44][45][46][47][48]. In this case, the dc self-bias is generated as a result of a so-called slope asymmetry as opposed to the previously discussed amplitude asymmetry.…”

High frequency sheath modulation and higher harmonic generation in a low pressure very high frequency capacitively coupled plasma excited by sawtooth waveform

“…Such waveforms are known as "Tailored Waveform" that are produced by incorporating higher harmonics in the sinusoidal waveform. The asymmetry produced by tailored waveforms is broadly classified into two categories: 1) amplitude asymmetry [60] and 2) temporal asymmetry [52][53]61]. In amplitude asymmetry, waveforms with varying minimum and maximum voltage/current excursions are used.…”

Capacitively coupled hydrogen plasmas sustained by tailored voltage waveforms: vibrational kinetics and negative ions control

“…The simulated Ion Flux Distribution Functions (IFDFs) were shown to be in good agreement with those measured experimentally with a Quadrupole Mass Spectrometer (QMS) coupled with an ion energy analyser. Also, the predictions of this hybrid model were compared to phase resolved optical emission spectroscopy (PROES) measurements [17,18], giving again a good agreement.…”