We report measurements of the breakdown curves for low-pressure rf capacitive discharges in nitrogen, hydrogen, argon, oxygen and ammonia. The electron drift velocity in these gases was deduced, as a function of reduced electric field, from the low-pressure turning points of the breakdown curves. The equation for rf breakdown proposed by Kihara (1952 Rev. Mod. Phys. 24 52) allows the position of both the turning point and the breakdown curve minimum to be calculated from the transport properties of each gas. Therefore we propose a new technique to determine the electron drift velocity from the position of the rf breakdown curve minima. We have determined the drift velocity in the range E/p = 52-1324 V cm −1 Torr −1 for nitrogen, E/p = 33-720 V cm −1 Torr −1 for argon, E/p = 32-713 V cm −1 Torr −1 for ammonia, E/p = 32-550 V cm −1 Torr −1 for hydrogen and E/p = 69-1673 V cm −1 Torr −1 for oxygen.

This paper shows that the rf capacitive discharge in NF 3 and SiH 4 can burn in three possible modes: weak-current α-mode, strong-current γ -mode and dissociative δ -mode. This new dissociative δ-mode is characterized by a high dissociation degree of gas molecules (actually up to 100% in NF 3 and up to 70% in SiH 4 ), higher resistivity and a large discharge current. On increasing rf voltage first we may observe a weak-current α-mode (at low NF 3 pressure the α-mode is absent). At rather high rf voltage when a sufficiently large number of high energy electrons appear in the discharge, an intense dissociation of gas molecules via electron impact begins, and the discharge experiences a transition to the dissociative δ-mode. The dissociation products of NF 3 and SiH 4 molecules possess lower ionization potentials, and they form an easily ionized admixture to the main gas. At higher rf voltages when near-electrode sheaths are broken down, the discharge experiences a transition to the strong-current γ -mode.

This paper demonstrates that the similarity law for the rf gas breakdown has the form U rf = ψ(p • L, L/R, f • L)(where U rf is the rf breakdown voltage, p is the gas pressure, L and R are the length and diameter of the discharge tube, respectively, f is the frequency of the rf electric field). It means that two rf breakdown curves registered for narrow inter-electrode gaps or in geometrically similar tubes and depicted in the U rf (p • L) graph will coincide only when the condition f • L = const is met. This similarity law follows from the rf gas breakdown equation and it is well supported by the results of measurements.

This paper presents the results of an experimental study of rf capacitive discharge in low-pressure SF 6 . The rf discharge in SF 6 is shown to exist not only in weak-current (α-) and strong-current (γ -) modes but also in a dissociative δ-mode. This δ-mode is characterized by a high degree of SF 6 dissociation, high plasma density, electron temperature and active discharge current, and it is intermediate between α-and γ -modes. The δ-mode appears due to a sharp increase in the dissociation rate of SF 6 molecules via electron impact starting after a certain threshold value of rf voltage. At the same time the threshold ionization energy of SF x (x = 1-5) radicals formed is below the ionization potential of SF 6 molecules. The double layer existing in the anode phase of the near-electrode sheath is shown to play an important role in sustaining the α-mode as well as the δ-mode but it is not a cause of the rf discharge transition from α-to δ-mode.

We report measurements of the breakdown curves of a radio-frequency capacitive discharge in low pressure ammonia. The electron drift velocity was determined from the location of turning points in the breakdown curves in the range of E/p = 42–713 V cm−1 Torr−1. We compare our results to values calculated from the published cross-sections in the range E/p = 1–5000 V cm−1 Torr−1 and find good agreement.

This paper reports current-voltage characteristics and pressure-voltage transition curves from the weak-current ␣-mode to the strong-current ␥-mode for rf capacitive discharges in N 2 O at frequencies of 2 MHz, 13.56 MHz, and 27.12 MHz. At 2 MHz the rf discharge is mostly resistive whereas at 13.56 MHz and 27.12 MHz it is mostly capacitive. The weak-current ␣-mode was found to exist only above a certain minimum gas pressure for all frequencies studied. N. Yatsenko ͓Sov. Phys. Tech. Phys. 26, 678 ͑1981͔͒ previously proposed that the ␣ − ␥ transition corresponds to breakdown of the sheaths. However, we show that this is the case only for sufficiently high gas pressures. At lower pressure there is a smooth transition from the weak-current ␣-mode to a strong-current ␥-mode, in which the sheaths produce fast electrons but the sheath has not undergone breakdown.

This paper reports measured and calculated breakdown curves in several gases of rf capacitive discharges excited at 13.56 MHz in chambers of three different geometries: parallel plates surrounded by a dielectric cylinder ͑"symmetric parallel plate"͒, parallel plates surrounded by a grounded metallic cylinder ͑"asymmetric parallel plate"͒, and parallel plates inside a much larger grounded metallic chamber ͑"large chamber"͒. The breakdown curves for the symmetric chamber have a multivalued section at low pressure. For the asymmetric chamber the breakdown curves are shifted to lower pressures and rf voltages, but the multivalued feature is still present. At higher pressures the breakdown voltages are much lower than for the symmetric geometry. For the large chamber geometry the multivalued behavior is not observed. The breakdown curves were also calculated using a numerical model based on fluid equations, giving results that are in satisfactory agreement with the measurements.

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