Estimation of the electron-collision initiation rate constant for the plasma polymerization and deposition of ethane using a transport-based model

The plasma polymerization and deposition of ethane in a parallel-plate electrode system was predicted using gas-phase transport equations and published gas-phase kinetic rate constants, with the assumption that the deposition rate was limited by the production of monomer free radicals and their diffusion to the deposition surface. The kinetic rate constant for radical initiation by electron collision with ethane was adjusted to bring the modelpredictionsfor mass deposition into line with experimental measurements reported in the literature for 12 combinations of power, gas fowrate, and pressure. Furthermore, the shapes of the predicted deposition profiles were made to closely match the experimental profiles by introducing an adjustable parameter to account for plasma boundary effects and two coefficients to account for nonradical polymerization (constant for all conditions). The best-fit electron-collision initiation constant was compared with theoretical predictions for oxygen and hydrogen in a manner explainable by bond strengths and vibrational degrees of freedom.