Very high frequency (VHF) driven capacitive discharges are now being increasingly adopted for
plasma-based materials processing due to their high processing rates and lower substrate damage. Past
studies related to complex plasma dynamics and higher harmonics generation in such systems were
limited to constant voltage/current conditions, whereas, industrial systems are mostly driven by
constant power density sources. In the present study, using particle-in-cell (PIC) simulation, we
explore the dynamics of collisionless symmetric capacitive discharges that is operated at constant
power densities. Our focus is on the effect of the driving frequency on the discharge parameters like
the electron density/temperature, the electron energy distribution function (EEDF), the ion energy
distribution function (IEDF), and the generation of higher harmonics in the device. The simulations
are performed for a driving frequency from 27.12-100 MHz in argon plasma at a gas pressure of 1 Pa
and for two values of the power density, namely, 2 kW/m3 and 20 kW/m3. It is observed that the
required discharge voltage for maintaining constant power density decreases and discharge current
increases with an increase in the driving frequency. A transition frequency is observed at both power
densities. The density decreases (electron temperature increases) before the transition frequency and
the trend is reversed after crossing the transition frequency. The EEDF shows an enhancement in the
population of the mid-energy range of electrons as the driving frequency increases up to the transition
frequency thereby changing the shape of EEDF from bi-Maxwellian to nearly Maxwellian, and then
transforms into a nearly bi-Maxwellian at higher driving frequencies. The IEDF at the electrode
surface shows bimodal behaviour at a lower driving frequency, becoming more pronounced at a power density of 20 kW/m3, and then turning into a single energy peak. The corresponding maximum
ion energy is found to decrease with driving frequency.
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Funders:
Board of Research in Nuclear Sciences (BRNS Sanctioned No. 39/14/05/2018-BRNS), Science and Engineering Research Board EMEQ program (SERB Sanctioned No. EEQ/2017/000164), Infosys Foundation Young Investigator grant, National Science Academy (INSA) for their support under the INSA Senior Scientist Fellowship scheme
ID Code:
27104
Deposited On:
09 May 2022 13:41 by
Miles Turner
. Last Modified 09 May 2022 15:38