Surface modification of PS polymer by oxygen-atom treatment from remote plasma: Initial kinetics of functional groups formation

Abstract

Self-limiting surface reactions are promising for atomic layer etching of materials. Classical treatments with plasmas do not allow for self-limiting functionalization but cause the formation of several functional groups and degradation. To avoid this, the polystyrene was oxidized in the plasma afterglow with the O-atom density 7 × 1017 m−3 and dissociation fraction 7%. X-ray Photoelectron Spectroscopy was used to study the formation of various oxygen groups versus the O-atom dose. The surface was saturated with the OH groups already after the dose of 1 × 1019 m−2, indicating a large initial sticking. The functionalization remained almost intact over an order of magnitude larger doses. Measurable quantities of the CO groups appeared simultaneously with the benzene ring's degradation at a dose of 1 × 1020 m−2. The ring degradation was accomplished with a significant increase in the OH concentration what was explained by the formation of a thicker oxygen-rich film. OCO and O(CO)O groups appeared after the dose of 1 × 1021 m−2, i.e., a 100-times larger dose than required for the initial saturation with the OH. The observations are sound with the predictions from the literature obtained through the density functional theory of oxygen adsorption on polystyrene.