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Absolute intensities of the vacuum ultraviolet spectra in oxide etch plasma processing discharges

Woodworth, Joseph R.; Riley, Merle E.; Amatucci, Vincent A.; Hamilton, Thomas W.; Aragon, Ben P.

In this paper, the authors report the absolute intensities of ultraviolet light between 4.9 eV and 24 eV ( 250 nm to 50 mn ) striking a silicon wafer in a number of oxide-etch processing discharges. The emphasis is on photons with energies greater than 8.8 eV, which have enough energy to damage SiO{sub 2}. These discharges were in an inductively-driven Gaseous Electronics Conference reference cell which had been modified to more closely resemble commercial etching tools. Comparisons of measurements made through a side port in the cell and through a hole in the wafer indicate that the VUV light in these discharges is strongly trapped. For the pure halocarbon gases examined in these experiments (C{sub 2}F{sub 6}, CHF{sub 3}, C{sub 4}F{sub 8}), the fluxes of VUV photons to the wafer varied from 1 x 10{sup 15} to 3 x 10{sup 15} photons/cm{sup 2} sec or equivalently from 1.5 to 5 mW/cm{sup 2}. These measurements imply that 0.1% to 0.3% of the rf source power to these discharges ends up hitting the wafer as VUV photons for the typical 20 mT, 200 W rf discharges. For typical ashing discharges containing pure oxygen, the VUV intensities are slightly higher--about 8 mW/cm{sup 2} . As argon or hydrogen diluents are added to the fluorocarbon gases, the VUV intensities increase dramatically, with a 10/10/10 mixture of Ar/C{sub 2}F{sub 6}/H{sub 2} yielding VUV fluxes on the wafer 26 mW/cm{sup 2} and pure argon discharges yielding 52 mW/cm{sup 2} . Adding an rf bias to the wafer had only a small effect on the VUV observed through a side-port of the GEC cell.