Higher Order Harmonics Are Suppressed in RF Capacitively Coupled Ar Plasmas Using an External Impedance Circuit

Different
$\pi $
-type matching networks (MI, MII, and MIII external circuits) are designed to study the symmetrical geometry discharge characteristic in capacitively coupled Ar plasma [capacitively coupled plasma (CCP)] in radio frequency (RF) (13.56 MHz) by using the global model. The plasma density and electron temperature are calculated by the modified Boltzmann method by optical emission spectra (OES), and the voltage of the variable capacitor in the external circuit is measured by an oscilloscope. The basic physical quantities (current and voltage of each branch, sheath capacitance, plasma inductance, plasma resistance, impedance, and efficiency) are calculated by the global model when the nonlinear relationship between capacitances (
$C_{m1}$
and
$C_{m2}$
) of matching networks is given. The results show that the significant third harmonic has two main sources, and most of them are from the matching network because of the resonance effect with the external circuit. A small part of it comes from the plasma series resonance (PSR) effect, which is due to the nonlinear interaction between the sheath and the bulk in the plasma discharge. The different matching network has a big effect on the CCP discharge. The MI external circuit can significantly suppress different high-order harmonics and minimize the influence of the external circuit on the plasma discharge.