Harmonic suppression and uniformity improvement of plasma density in capacitively coupled plasma

Abstract

A method for improving plasma uniformity in capacitively coupled plasma (CCP) is developed. Plasma contains harmonics due to the nonlinear characteristics of the sheath. Because high-frequency harmonic components in the plasma have short wavelengths, high-frequency harmonics components have a bad influence on plasma uniformity. This is because the electromagnetic standing wave effect (SWE) is severe at high frequencies. To improve plasma uniformity, a CCP using a parallel capacitor that is connected to the powered electrode is developed. By adjusting the capacitance of the parallel capacitor, a parallel resonance between the parallel capacitor and the reactor, which is net inductive, is generated. As the parallel loop approaches the parallel resonance, the currents of other harmonic frequency components in the plasma are greatly reduced. Therefore, the waveform of the plasma bulk current also becomes sinusoidal, and the amplitude of the plasma current becomes almost constant, regardless of the radial position at the parallel resonance condition. Moreover, the voltage applied across the plasma is greatly increased. Consequently, plasma uniformity and the voltage applied to the plasma along the electrode are significantly improved under the parallel resonance condition due to a greatly reduced SWE.