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

Abstract

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 positive ion density from 1.8 × 1011 to 1.4 × 1011 cm-3, over the same range. OE spectroscopy is also used to estimate the rate constant for the dissociative excitation of Cl2 to the Cl (4p2D0J′ = 3/2,5/2) excited state with emission at 822.2 nm, yielding ∼10-13 cm3s-1. © 2001 American Institute of Physics.