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

Optical emission (OE) actinometry has been used to measure the absolute densities of Cl, Cl, Cl, and Ar in a high-density inductively coupled (ICP) Cl-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 to Cl increases with rf power, with the dissociated fraction increasing from 78% to 96% at 600 W (10.6 W cm) 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 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 positive ion density from 1.8 × 10 to 1.4 × 10 cm, over the same range. OE spectroscopy is also used to estimate the rate constant for the dissociative excitation of Cl to the Cl (4pDJ′ = 3/2,5/2) excited state with emission at 822.2 nm, yielding ∼10 cms. © 2001 American Institute of Physics.