Time-dependent heating rates of argon plasmas with molecular gases

The replacement of a traditional matching network with a matchless RF pulser enables rapid pulsing and faster electron density rates of rise. Electron densities on the order of 1 x 1011 cm-3 have been achieved in sub 25 microsecond time scales, or equivalently density rates of rise exceeding 4 x 1015 cm-3 s-1, via H-mode heating in a pure argon ICP. Time-resolved electron density measurements show evidence of time-dependent heating rates with the introduction of molecular gases into the argon plasma; this is a possible indication that there are limitations to rapid pulsing for reactive chemistry formation in pulsed RF systems. The sub microsecond time resolution for the density measurements, taken with a microwave hairpin probe, reveals that the initial ionization rate tracks with a pure argon plasma until a breakpoint occurs where the electron density splits. This suggests that the effects of the molecular gas do not immediately contribute to plasma density formation. The hairpin probe data is compared with a 0D kinetic model in order to better determine why the break does not occur instantly. This research will help determine the minimum duty cycle that a plasma needs to be pulsed in order to fully achieve optimal effects of plasma chemistry formation in short duty cycle plasma heating systems.