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 Cl2, Cl, Cl+, and Ar+ in a high-density inductively coupled (ICP) Cl2–Ar plasma at 18 mTorr as a function of the 13.56 MHz radio frequency (rf) power and Ar fraction. The fractional dissociation of Cl2 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 (Cl2 and Cl) to ion (Cl+ and Ar+) flux ratio is found to be strongly dependent on Ar fraction, decreasing by a factor of ∼3.0 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 pos...

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