Validation of Etching Model of Polypropylene Layers Exposed to Argon Plasmas

Thin layers of polypropylene (PP) have been treated by argon low-temperature plasmas in an inductively coupled plasma setup. The etched thickness of PP was monitored in situ by means of single-wavelength ellipsometry. The ellipsometric model of the polymer surface exposed to plasma consists of a UV-modified layer, a dense amorphous carbon layer because of ion bombardment, and an effective medium approximation layer, which accounts for moderate surface roughness. The etching behavior has been compared to a model based on argon ion beam irradiation experiments. In this approach, surface processes are described in terms of etching yields and crosslinking probabilities as a function of incident fluxes and energies of Ar ions and UV photons. The ion beam model fits well with the plasma etching results.