Paper PS-WeA3
INVITED TALK: Rare Gas Actinometry Turns Thirty Nine and is Still Finding Applications

Wednesday, October 23, 2019, 3:00 pm, Room B130

Ever since the first paper on rare gas actinometry (as it would later be called), published by Coburn and Chen, this method has been widely used to measure relative and sometimes absolute number densities of atoms and small molecules. The problem originally chosen by Coburn and Chen of measuring F atom densities with Ar as the rare gas turns out to be one of the most reliable applications of this diagnostic method, for an important etchant species that is difficult to detect by other techniques. The precision of F-atom actinometry can be attributed, first, to the (apparent) match between the relative energy dependence for the electron-impact excitation cross section of F 703.7 nm emission, compared with that for Ar 2p₁ emission at 750.4 nm. Second, the large degree of dissociation for even moderate density plasmas with typical feed gases (CF₄/O₂, SF₆, NF₃, etc.), produces high F concentrations, so dissociative excitation of F emission from other F-containing species is usually negligible. This talk will briefly review actinometry as a plasma diagnostic with an emphasis on the issues related to its quantitative application, including cases where it can be used reliably, and others that should be interpreted with caution. Recent experiments that highlight the power of this technique will be discussed, including several studies relying on other work by John Coburn.