Study On The Series Resonance Effect Of Low Pressure Capacitively Coupled Ar Plasma

Low temperature capacitively coupled plasma device has the advantages of simple structure,uniform discharge and stable working state.In recent years,it has been widely used in industry,especially in the field of micro-nano electronic device processing.With the maturity of related technologies and the increasing demand for their processes,there are higher requirements for the operating speed and machine throughput of product production.Up to now,because the plasma is much more complex than the non-ionized gas,many related internal discharge mechanisms have not been fully understood,especially in the electronic heating mechanism.In this paper,emission spectrum,PIC/MCC simulation and global model are used to systematically study the characteristics of low-pressure RF capacitively coupled plasma,which is mainly divided into three parts to study the plasma series resonance effect and matching network.(1)In the first part of the work,the discharge voltage and current waveforms of single-frequency and dual-frequency capacitively coupled plasmas were measured through experiments.The measured voltage waveforms were taken as the input parameters of PIC/MCC simulation for numerical calculation and analysis,and the spatiotemporal distribution of plasma basic physical parameters(electron density,electron temperature,electric field,electron current density and electron heating rate)with RF power was obtained.More importantly,the simulated current density is consistent with the change trend of the discharge current waveform measured in the experiment.Using the Fast Fourier transform,it is found that the current and current density have irregular waveform distortion,and the generated higher harmonics are caused by the plasma series resonance effect.(2)In the second part of the work,the voltage and current waveforms and emission spectra of geometrically symmetric dual-frequency capacitively coupled plasma were measured by experiments.The nonlinear global model was used to calculate the sheath charge,bias voltage and plasma RF current with time under different low-frequency power,considering the dual-frequency coupling effect and not considering the coupling effect.In addition,we also get the change of current amplitude at different frequencies in the matching network.It is found that the higher harmonic in the plasma current is not only caused by the series resonance of the plasma,but also caused by the resonance in the matching network.(3)In the third part of the work,different Π Type matching network(M,MI,MII and MIII external circuits),calculate the electron density and electron temperature according to the emission spectrum method,and measure the voltage of the variable capacitance in the external circuit by connecting the high-voltage probe with the oscilloscope.When the nonlinear relationship between variable capacitors Cm1 and Cm2 is given,the basic physical quantities(current and voltage of each branch,sheath capacitance,plasma inductance,plasma resistance,impedance and efficiency)are calculated through including a nonlinear global model for Π type matching networks.The results show that there are two sources of the most significant third harmonic,most of which are transmitted by the matching network(mainly the resonance effect with the external circuit),and a small part is from the plasma series resonance effect(due to the nonlinear interaction between the sheath and the plasma region in the plasma discharge).MI external circuit can significantly suppress the generation of harmonics.