Electrical circuit of the planar RF antenna.
Current distributions in the conductive legs for different modes of a 23-leg RF antenna. The symbols indicate the currents in each leg; the lines show the mode structure.
(a) Schematic top view of the planar RF antenna showing the antenna bars (inductance L), the capacitors (C), and the matching network. (b) Schematic end view of the antenna showing the grounded metal baseplate, the metal frame sidewalls, and the antenna embedded in the dielectric with a protective glass cover. A substrate can be placed above the plasma as shown. The whole assembly is placed within the vacuum vessel.
Measured resonance spectrum of the 23-leg planar RF antenna. Figure taken from Ref. 8.
The antenna impedance magnitude (squares) and phase (circles) measured in the neighborhood of the m = 6 mode (a) without plasma; and (b) with a low power plasma (80 W). For comparison, the lines show fitted curves using a parallel resonance equivalent circuit for each case: (a) 13.13 nF in parallel with 10.55 nH and 2.65 m in series; (b) 15.09 nF in parallel with 9.166 nH and 6.68 m in series. The dotted lines show the shift in the resonance frequency from 13.525 MHz (in vacuum) to 13.532 MHz for the low power plasma.
(a) Calculated (red) and measured (black) current amplitudes in the legs of the planar RF antenna for the mode m = 6. (b) Calculated (red and blue dashed-lines) and measured (green and black solid lines) voltage amplitudes at the nodes of the planar RF antenna for the mode m = 6. Figure taken from Ref. 8.
Normalized electron density surface obtained with Langmuir probes at about 4 cm above the antenna and at a power of 1000 W. The Ar flux is 10 sccm and the pressure mbar. A floating metallic substrate is placed 8 cm above the RF antenna. The level-lines in the contour plot are separated by 10%.
Images (a) and (c) present measured electron density profiles at 20 W and 1000 W, respectively, at a distance of 2 cm from the antenna. The Ar flux is 50 sccm and the pressure is mbar. Images (b) and (d) present calculated electric field magnitude profiles in a parallel plane 2 cm above the antenna defined in the first case (b) by its voltages at each node and in the second case (d) by its voltages at each node and its currents in each segment.
Electron density profiles (normalized) along the RF antenna length at 100, 200, and 1000 W at a distance of 4 cm above the antenna. The Ar pressure is mbar, and the flux is 10 sccm. The black line segments indicate the positions of the legs with maximal currents, that is to say, leg number 4, 8, 12, 16, and 20, as in Fig. 6(a).
Maximum electron density measured by 33 GHz interferometer in the Ar plasma for increasing RF power going from 30 W to 2000 W. The Ar pressure is mbar, and the flux is 30 sccm. The transition from capacitive to inductive coupling occurs at around 60 W.
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