Power dissipation in capacitively coupled rf discharges

Abstract

The power dissipation in capacitively coupled rf discharges (Ar, 400 Pa) has been studied by impedance measurements in the 10–50 MHz frequency range. The article focuses on electrodeless discharge configurations in which the field-supplying electrodes are separated from the discharge volume by a dielectric wall, but the study of a classical electroded rf discharge is also included for comparison. The power share between bulk plasma and sheath regions is determined quantitatively using an equivalent circuit model which reflects the discharge structure. It depends strongly on both rf discharge current and frequency. For the electrodeless discharge configurations and equally for the electroded one, the fraction of power dissipated in the sheaths generally increases with increasing current and decreasing frequency. The sheath thickness derived from the impedance measurements decreases with frequency. It is nearly independent of the current for the electrodeless discharge configurations, but decreases with increasing current for the discharge configuration with internal metallic electrodes. A model for the power dissipation in the sheath is based on the current-voltage characteristics of a space-charge-limited ion current. It allows the calculation of the dissipated power Ps for operator set discharge conditions such as rf current, frequency, electrode area, and gas pressure, and predicts that Ps should vary with current I and frequency ω as (I/ω)5/2. The model is in good agreement with the experimental data. The contribution to the power dissipation from further processes besides the ion current in the sheath is also examined.

Amorphous solar cells, the micromorph concept and the role of VHF-GD deposition technique

“…Both these observations are in agreement with experimental and theoretical studies by other groups (Beneking, 1990;Beneking et al, 1992;Surendra and Graves, 1991) and can be considered to constitute a general physical effect prevalent in capacitively-coupled VHF-plasmas. There are two consequences of the thinner plasma sheaths and the lower RF-voltage on the powered electrode: first, the sheath potential and, hence, the ion bombardment on the growing layer is reduced; second, the RF-power is more efficiently coupled-in into the bulk plasma (rather than into the sheath, as is the case at lower plasma excitation frequencies).…”

Alternative designs for nanocrystalline silicon solar cells

“…Most of the voltage gets dropped across the sheaths. to reach the electrode after many cycles thus having a time averaged energy [86]. The higher frequency thus leads to lower ion energy and also thinner sheaths.…”

The effect of electrode heating on the discharge parameters in complex plasma experiments

“…In this case, the impedance of the plasma can be represented by two sheath reactances, X s , in series with the bulk resistance R b [20]. Since the dissipative character of the sheaths is much smaller than the bulk, they are considered to be completely capacitive, and hence their impedance is purely imaginary.…”

“…The results are shown in figure 11. In a capacitively coupled RF discharge in argon at the pressures and powers considered, the bulk resistance can be approximated by R b = ν c /ω 2 p ǫ 0 , with ν c = n gas σv e f e dv e the electron-neutral collision frequency, σ the cross section for elastic electron-neutral collisions [20], which is approximately 3 × 10 −19 m 2 for the electron energies in the discharge [21], and ω p = n e e 2 /m e ǫ 0 the electron plasma oscillation frequency. Hence, R b ≈ 3 × 10 −19 m e n gas 8k B T e /πm e /n e e 2 ≈ 10 −7 (n gas /n e ) √ T e Ohm, where we have assumed a Maxwellian distribution for the electrons.…”