Series resonance effects of a variable inductor termination on the nonpowered electrode in capacitively coupled plasmas

The effect of LC series resonance on the voltage of a nonpowered electrode in a capacitively coupled plasma is investigated by connecting a variable inductor to the nonpowered electrode. Two distinct LC series resonances are observed while varying the reactance of the variable inductor. The first resonance occurs between an inductor and a vacuum variable capacitor, thereby resulting in the voltage of the nonpowered electrode approaching zero. The reactance between the inductor and the vacuum variable capacitor is minimized at this resonance, thereby enabling the nonpowered electrode voltage to remain close to 0 V even with increased applied RF power. The second resonance is a series resonance between the variable inductor and the nonpowered electrode sheath, leading to a maximization of the nonpowered electrode voltage. The reactance between the variable inductor and the nonpowered electrode sheath is minimized at this resonance. As the applied RF power increases under the second resonance condition, the voltage of the nonpowered electrode increases, thereby resulting in a significant increase in the maximum electron density by approximately 35%. This increase in the electron density at the second resonance can be attributed to enhanced stochastic heating due to the sharp increase in the sheath voltage.