Simulation Of Capacitively Coupled Plasma Driven By Frequency And Amplitude Modulation RF Source

Capacitively Coupled Plasma(CCP)is widely used in plasma etching and deposition processes because of its low cost,simple structure,and easy generation of large-area uniform plasma.In order to achieve reliable regulation of plasma parameters,new discharge methods like dual-frequency,VHF,magnetization CCP and electrical asymmetry effect(EAE)have been proposed beyond the earliest single-frequency CCP discharge,which has been widely used in various fields.However,the methods mentioned above all discharge with a fixed frequency power source.So far,there is no research on CCP which is driven by a variable frequency power source.In this paper,a simulation of CCP driven by FM and AM RF sources is carried out with a onedimensional Particle-in-Cell/Monte Carlo collision(PIC/MCC)model.A chirp RF source with a low frequency of 2 MHz,a high frequency of 18 MHz,and a frequency modulation period of 5 μs is applied.The power waveform consists of an up chirp and a down chirp.The research indicates that the CCP driven by a frequency-modulated radio frequency source can maintain a stable glow discharge and form a time-varying plasma with a time-periodic density.The plasma density,electron and ion current,temperature and heating rate,ion flux and energy on the electrodes have fluctuations consistent with the frequency modulation period and are approximately sinusoidal in form.However,the fluctuations are observed to have a certain delay.The electron and ion energy distribution function can also be modulated by the frequency variation of the FM source.A multi-peak structure that varies and shifts with frequency variation is observed in the ion energy distribution function.With the chirp rate reduced,the electron and ion density increases while the electron temperature decreases.The ion flux fluctuation amplitude on the electrode increases with the decrease of the chirp rate,and the retardation decreases,while the ion energy is almost unchanged.In addition,the CCP discharges driven by coupled FM and AM waveforms are also studied.The effects of the coupling phase difference of 0 and π on the discharge and differences with the case without chirp are discussed.The results show that when the phase difference is 0,the plasma density,electron current and electron heating rate increase rapidly during the up-chirp due to the superposition of energy gains,and the peaks are higher than those cases without chirp and the phase difference of π.When the phase difference is π,since the frequency peak and the amplitude peak differ by half the modulation period,the power absorption is reduced,the changes of the above parameters are slowed down,and the peak value is lower than the case of no chirp.Because the mass of ions is much higher than that of electrons,they behave differently under the same phase difference.The peak of the ion temperature appears at the low voltage of the amplitude modulation but not with the phase difference.When the phase difference is π,the gain of the ion is superimposed due to the low frequency and high pressure.The peak is higher than the other two cases.The phase of the ion flux and energy fluctuations on the plate is consistent with the amplitude modulation.In summary,electron kinetics are more affected by frequency modulation components,while ion kinetics are more affected by amplitude modulation components.