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Very high frequency (VHF) driven capacitive discharges are now beingincreasingly adopted for plasma-based materials processing due to their highprocessing rates and lower substrate damage. Past studies related to complexplasma dynamics and higher harmonics generation in such systems were limited toconstant voltage/current conditions, whereas, industrial systems are mostlydriven by constant power density sources. In the present study, usingparticle-in-cell (PIC) simulation, we explore the dynamics of collisionlesssymmetric capacitive discharges that is operated at constant power densities.Our focus is on the effect of the driving frequency on the discharge parameterslike the electron density/temperature, the electron energy distributionfunction (EEDF), the ion energy distribution function (IEDF), and thegeneration of higher harmonics in the device. The simulations are performed fora driving frequency from 27.12-100 MHz in argon plasma at a gas pressure of 1Pa and for two values of the power density, namely, 2 kW/m3 and 20 kW/m3. It isobserved that the required discharge voltage for maintaining constant powerdensity decreases and discharge current increases with an increase in thedriving frequency. A transition frequency is observed at both power densities.The density decreases (electron temperature increases) before the transitionfrequency and the trend is reversed after crossing the transition frequency.The EEDF shows an enhancement in the population of the mid-energy range ofelectrons as the driving frequency increases up to the transition frequencythereby changing the shape of EEDF from bi-Maxwellian to nearly Maxwellian, andthen transforms into a nearly bi-Maxwellian at higher driving frequencies.

Driving frequency effect on discharge parameters and higher harmonic generation in capacitive discharges at constant power densities