Effects of atomic chlorine wall recombination: Comparison of a plasma chemistry model with experiment

Abstract

Results from a plasma chemistry model provide predictions of spatially and temporally averaged plasma properties. Application of the model to chlorine-etch process conditions, typical of a high plasma-density transformer coupled plasma reactor, provides plasma composition dependence on reactor operating parameter such as power and pressure. Model results also show the dependence of species concentrations on the atomic-chlorine recombination rate at reactor walls. Comparison of model predictions to measured composition trends as determined by Langmuir probe, actinometry, and ion-energy analysis reveals a critical wall-recombination probability of about 0.1 for chlorine atoms on a chlorinated anodized-aluminum surface. At or above this critical value, the model reproduces the experimentally observed trends, while employing a recombination probability below this value results in predictions that are inconsistent with the data. The model determines gas-phase and surface-species compositions in plasma-etch reactors through the solution of species, mass, electron-energy, and surface-site conservation equations. The use of well mixed reactor approximations reduces the computational expense of detailed kinetics calculations and allows investigation into the dependence of plasma chemistry on uncertain kinetic parameters. The dominance of surface reaction rates in determining plasma properties is expected to be equally important in more complex two-dimensional inductively coupled plasma models due to the highly diffuse nature of these low-pressure reactors.