Absolute cross sections for fluorine 3p→3s line emissions following single electron impact on NF3, CF4, and SF6

Abstract

We studied the dissociation of the fluorine-containing molecules NF3, CF4, and SF6 by controlled electron impact in a crossed electron beam–gas beam apparatus. Absolute emission cross sections and appearance potentials were determined for the most intense 3p→3s atomic fluorine lines in the visible range of the optical spectrum between 6200 and 7800 Å. These lines are emitted by atomic fluorine fragments that are formed in the various excited states associated with the 1s22s22p43p electron configuration. The energy dependence for all cross sections indicated that optically allowed, electric dipole excitation of the parent molecule plays the leading role. For a particular line the absolute emission cross sections were found to decrease from NF3 to CF4 to SF6. The measured onset potentials indicated that in all cases total fragmentation of the molecule is a dominant process. NF3, CF4, and SF6 are the main constituents of etchant gas plasmas that are widely used in various areas of semiconductor processing. An attempt is made to relate our single collision results to results obtained in optical studies of rf processing plasmas.