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In most PIC/MCC simulations of radio frequency capacitively coupled plasmas(CCPs) several simplifications are made: (i) fast neutrals are not traced, (ii)heavy particle induced excitation and ionization are neglected, (iii) secondaryelectron emission from boundary surfaces due to neutral particle impact is nottaken into account, and (iv) the secondary electron emission coefficient isassumed to be constant, i.e. independent of the incident particle energy andthe surface conditions. Here we question the validity of these simplificationsunder conditions typical for plasma processing applications. We study theeffects of including fast neutrals and using realistic energy-dependentsecondary electron emission coefficients for ions and fast neutrals insimulations of CCPs operated in argon at 13.56 MHz and at neutral gas pressuresbetween 3 Pa and 100 Pa. We find a strong increase of the plasma density andthe ion flux to the electrodes under most conditions, if these processes areincluded realistically in the simulation. The sheath widths are found to besignificantly smaller and the simulation is found to diverge at high pressuresfor high voltage amplitudes in qualitative agreement with experimentalfindings. By switching individual processes on and off in the simulation weidentify their individual effects on the ionization dynamics and plasmaparameters. We conclude that fast neutrals and energy-dependent secondaryelectron emission coefficients must be included in simulations of CCPs in orderto yield realistic results.

Effects of fast atoms and energy-dependent secondary electron emission yields in PIC/MCC simulations of capacitively coupled plasmas