Absolute intensities of the vacuum ultraviolet spectra in a metal-etch plasma processing discharge

In this article we report absolute intensities of vacuum ultraviolet (VUV) and near ultraviolet emission lines (4.8–18 eV) for discharges used to etch aluminum in a commercial inductively coupled plasma reactor. We report line intensities as functions of wafer type, pressure, gas mixture, and radio frequency excitation level. In a standard aluminum etching mixture containing Cl2 and BCl3 almost all the light emitted at energies exceeding 8.8 eV was due to neutral atomic chlorine. Optical trapping of the VUV radiation in the discharge complicates calculations of VUV fluxes to the wafer. However, we measured total photon fluxes to the wafer at energies above 8.8 eV on the order of 4×1014 photons/cm2 s with a nonreactive wafer and 0.7×1014 photons/cm2 s with a reactive wafer. The majority of the radiation was between 8.9 and 9.3 eV. At these energies, the photons have enough energy to create electron-hole pairs in SiO2 and may penetrate up to a micron into the SiO2 before being absorbed. Relevance of these measurements to VUV photon-induced damage of SiO2 during etching is discussed.