Ion energy distributions and optical emission spectra in NF3-based process chamber cleaning plasmas

To minimize ion bombardment induced damage in NF3-based chamber cleaning plasmas, we have studied the effects of diluent gases and reactor pressure on ion energy distribution functions in NF3 plasmas. We have utilized plasma ion mass spectrometry, ion energy analysis, and optical emission spectroscopy in 25 mol % NF3 plasmas with argon, helium, and oxygen diluents. We have also compared the NF3-based plasma measurements to those of 50 mol % C2F6/O-2 plasmas. We have demonstrated that diluting with helium and operating at higher pressures will reduce ion energies in NF3 plasmas while maintaining superior chamber cleaning performance. In addition, we have correlated the intensity ratio of specific argon emission lines to average ion energies at the grounded electrode. This correlation provides a practical diagnostics tool for further optimization work. (C) 2001 American Vacuum Society.