Optical plasma emission spectroscopy of etching plasmas used in Si-based semiconductor processing

Previously published applications of optical emission spectroscopy as a quantitative plasma diagnostic technique are reviewed. By adding traces of rare gases to the plasma, electron temperatures (T-e) and relative electron and ion densities can be determined from electron impact-induced optical emission. Excitation from both the ground state and metastable states of the rare gases must be considered. At higher rare gas partial pressures, UV radiation trapping and optical cascading must also be taken into account. Absolute species concentrations (e.g. Cl-2, Cl, O, and F) can be derived from their optical emissions, combined with T-e measurements determined from rare gas optical emission. Examples are given of neutral and ion species density measurements in chlorine, oxygen, and fluorocarbon-containing low-pressure, high charge-density plasmas. Typical results of T-e measurements are also presented and compared with Langmuir probe measurements.