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

In this article, we report the absolute intensities of ultraviolet light be tween 4.9 and 24 eV (250 to 50 nm) striking a silicon wafer in a number of oxide etch processing discharges. Our emphasis is on photons with energies greater than 8.8 eV,which have enough energy to damage SiO2. These discharg es were in an inductively driven Gaseous Electronics Conference (GEC) refer ence cell which had been modified to more closely resemble commercial etchi ng tools. Comparisons of measurements made through a side port in the cell and through a hole in the wafer indicate that the vacuum ultraviolet (VUV) light in these discharges is strongly trapped. For the pure halocarbon gase s examined in these experiments (C2F6. CHF3, C4F8), the fluxes of VUV photo ns to the wafer varied from 1 to 3x10(15) photons/cm(2)s or equivalently fr om 1.5 to 5 mW/cm(2). These measurements imply that 0.1%-0.3% of the rf sou rce power to these discharges ends up hitting the wafer as VUV photons for our typical 20 mT, 200 W rf discharges. For typical "ashing" discharges con taining pure oxygen, the VUV intensities are slightly higher-about 8 mW/cm( 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/C2F6/H -2 yielding VUV fluxes on the wafer 26 mW/cm(2) and pure argon discharges y ielding 52 mW/cm(2). Adding a rf bias to the wafer had only a small effect on the VUV observed through a side port of the GEC cell. (C) 2001 American Vacuum Society. [DOI: 10.1116/1.1335685].