High frequency sheath modulation and
higher harmonic generation in a low
pressure very high frequency
capacitively coupled plasma excited by
sawtooth waveform
Sharma, SarveshwarORCID: 0000-0002-0642-0247, Sirse, NishantORCID: 0000-0002-7063-4100 and Turner, Miles M.ORCID: 0000-0001-9713-6198
(2020)
High frequency sheath modulation and
higher harmonic generation in a low
pressure very high frequency
capacitively coupled plasma excited by
sawtooth waveform.
Plasma Sources Science and Technology, 29
(11).
ISSN 0963-0252
A particle-in-cell (PIC) simulation study is performed to investigate the discharge
asymmetry, higher harmonic generations and electron heating mechanism in a low
pressure capacitively coupled plasma (CCP) excited by a saw-tooth like current
waveform for different driving frequencies; 13.56 MHz, 27.12 MHz, and 54.24 MHz.
Two current densities, 50 A/m2 and 100 A/m2 are chosen for a constant gas pressure
of 5 mTorr in argon plasma. At a lower driving frequency, high frequency
modulations on the instantaneous sheath electric field near to the grounded electrode
are observed. These high frequency oscillations create multiple ionization beam like
structures near to the sheath edge that drives the plasma density in the discharge and
responsible for discharge/ionization asymmetry at lower driving frequency.
Conversely, the electrode voltage shows higher harmonics generation at higher
driving frequencies and corresponding electric field transients are observed into the
bulk plasma. At lower driving frequency, the electron heating is maximum near to the
sheath edge followed by electron cooling within plasma bulk, however, alternate
heating and cooling i.e. burst like structures are obtained at higher driving
frequencies. These results suggest that electron heating in these discharges will not be
described accurately by simple analytical models.