Equilibrium and relaxation of particulate charge in fluorocarbon plasmas

Charging of micron-size particulates, often appearing in fluorocarbon plasm a etching experiments, is considered. It is shown that in inductively coupl ed and microwave slot-excited plasmas of C4F8 and Ar gas mixtures, the equi librium particle charge and charge relaxation processes are controlled by a combination of microscopic electron, atomic (Ar+ and F+), and molecular io n (CF3+, CF2+, and CF+) currents. The impact of molecular ion currents on t he particulate charging and charge relaxation processes is analyzed. It is revealed that in low-power (<0.5 kW) microwave slot-excited plasmas, the im pact of the combined molecular ion current to the total positive microscopi c current on the particle can be as high as 40%. The particulate charge rel axation rate in fluorocarbon plasmas appears to exceed 10(8) s(-1), which i s almost one order of magnitude higher than that from purely argon plasmas. This can be attributed to the impact of positive currents of fluorocarbon molecular ions, as well as to the electron density fluctuations with partic le charge, associated with electron capture and release by the particulates . (C) 2001 American Institute of Physics.