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Schematics of experimental apparatus: (a) The plasma reactor and (b) the bottom matcher in which additional impedance control circuit was implemented. Although the apparatus had a dual frequency rf system, the 60 MHz power was not applied so as to make the effect of the harmonics of 13.56 MHz on electron density clear.
Reactance of bottom electrode at harmonic frequencies vs capacitance of IC-unit . Capacitances and correspond to 10 and 90 pF, respectively. The dotted-dashed line denotes . Only reactances and passed through the region of critical reactance, which is expected to be a small positive value close to the line.
(a) Current amplitudes of harmonic and fundamental components at the bottom electrode vs capacitance of IC-unit. The currents and exhibited resonant growth. (b) The electron densities vs capacitance . The center, middle, and edge densities are taken at the radii of 0, 80, and 150 mm, respectively. The center electron density clearly increased when the harmonic currents exhibited resonant growth. On the other hand, the electron densities at the middle and edge changed slightly.
Radial distribution of electron density. The capacitance values of 40, 340, and 1440 correspond to the off-resonance, fourth harmonic resonance, and third harmonic resonance, respectively. The broken lines in Fig. 3 denote those values.
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