Optical actinometry of Cl2, cl, Cl+, and Ar+ densities in inductively coupled Cl2-Ar plasmas

Optical emission (OE) actinometry has been used to measure the absolute densities of Cl-2, Cl, Cl+, and Ar+ in a high-density inductively coupled (ICP) Cl-2-Ar plasma at 18 mTorr as a function of the 13.56 MHz radio frequency (rf) power and Ar fraction. The fractional dissociation of Cl-2 to Cl increases with rf power, with the dissociated fraction increasing from 78% to 96% at 600 W (10.6 W cm(-2)) as the Ar fraction increases from 1% to 78% due to an increase in electron temperature. Emission from Cl+* and Ar+* originates primarily from electron excitation of Cl+ and Ar+ (and not excitation of Cl and Ar), making actinometric determination of Cl+ and Ar+ densities feasible. For powers exceeding 600 W, the neutral (Cl-2 and Cl) to ion (Cl+ and Ar+) flux ratio is found to be strongly dependent on Ar fraction, decreasing by a factor of similar to3.0 as the latter is increased from 13% to 78%. This dependence can be attributed mostly to the decrease in Cl density and relatively little to the small decrease in the total positive ion density from 1.8x10(11) to 1.4x10(11) cm(-3), over the same range. OE spectroscopy is also used to estimate the rate constant for the dissociative excitation of Cl-2 to the Cl (4p(2)D(0)J(')=3/2,5/2) excited state with emission at 822.2 nm, yielding similar to 10(-13) cm(3) s(-1). (C) 2001 American Institute of Physics.