Tailored voltage waveforms applied to a capacitively coupled chlorine discharge

Abstract

Tailored voltage waveform, composed of a fundamental frequency and the second harmonic, is applied to a capacitively coupled chlorine discharge operated in the pressure range 1–50 Pa. The electronegativity is very high and the electron power absorption is mainly due to drift-ambipolar (DA) electron power absorption within the electronegative core. For operating pressures of 1 and 10 Pa the creation of a dc self-bias and asymmetric response is demonstrated and applied to control the ion bombardment energy while the ion flux on the electrodes remains fixed. However, the available range in mean ion energy is rather limited and the range is significantly narrower than typically observed for electropositive discharges. For operating pressure of 50 Pa it is not possible to control the ion bombardment energy by the phase angle between the fundamental frequency and the second harmonic. At the low pressure of 1 Pa the power absorption by C l 2 + ions dominate, while power absorption by electrons is smaller. At higher operation pressure DA power absorption by electrons dominates. The electric field within the electronegative core is high and not constant within the plasma bulk and exhibits the waveform of the discharge driving voltage for both the single frequency and dual frequency operation.

Electron power absorption mode transition in capacitively coupled Ar/CF4 discharges: hybrid modeling investigation

“…Besides, by increasing gas pressure, Liu et al and Wen et al [13,33] reported the α to γ mode transition in Ar, whereas, the heating mode transited from the α to a combination of the α and DA mode, and finally into the DA mode in CF 4 [17]. When the ion plasma frequency becomes comparable to or higher than the driving frequency, a transition to the STR mode at high pressures was experimentally observed in CF 4 [34], and the similar conclusion has been obtained in Cl 2 gases [28] by simulation.…”

“…In electropositive gases, such as Ar, He and Ne, the discharge is either in the α mode or/and the γ mode [10,15,24,25]. By contrast, in electronegative plasmas, such as CF 4 , O 2 , SF 6 , SiH 4 , Cl 2 , the discharges may also work in the DA mode or/and the STR mode [26][27][28][29][30][31]. Through a combination of numerical simulation and experimental analysis, Donko et al [32] studied the effect of the gas mixture ratio in Ar/CF 4 discharges, and they confirmed that when the proportion of Ar was relatively high, the discharge changed from the DA to the α mode, or even the γ mode if the secondary electron emission (SEE) coefficient is high enough.…”

Investigation of the dual-frequency bias effect on inductively coupled Cl2 plasmas by hybrid simulation

“…Actually, the coupling effect has also been observed in traditional dual frequency (DF) capacitively coupled plasmas (CCPs) [22][23][24][25][26][27][28][29][30]. Therefore, the electrically asymmetric discharge, which is driven by a fundamental frequency and its second harmonic, has been proposed to ideally realize the separate control of the ion flux and ion energy on the substrate [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48]. Heil et al [31] first revealed that a DC self-bias was generated due to the discharge asymmetry, and it almost changed linearly with the phase shift between the two frequencies, i.e.…”

Electron power absorption in capacitively coupled neon-oxygen plasmas: a comparison of experimental and computational results

“…The spatio-temporal distributions of the electron power absorption and the ionization within the radiofrequency (RF) period determine the operation mode of the discharge. In low-pressure CCPs, several different discharge operation modes can be identified: the α-mode and the γ-mode [6] are typical in electropositive gases, while the driftambipolar (DA) mode [7] and the striation (STR) mode [8][9][10][11][12] can be observed in electronegative gases. In the α-mode, the ionization, caused by energetic electrons accelerated by electric fields during the times of sheath expansion, is concentrated at the bulk side of the expanding sheath edge, while in the γ-mode, the ionization, dominated by secondary electrons (SEs) accelerated by the strong electric field inside the sheaths, is concentrated within the sheath region.…”