X-ray photoelectron spectroscopy study of polymer surface reactions in F2 and O2 gases and plasmas

Abstract

The surface kinetics of polystyrene, polyparaphenylene, and polyvinylmethylketone films in oxygen and fluorine plasmas was studied in a novel reactor which exposes a sample maintained in high vacuum to the species present in a plasma. These polymers were chosen as they contain the same chemical functional groups found in polymers currently used in the semiconductor industry. The reactor configuration enabled the determination of the surface composition using x-ray photoelectron spectrometry as a function of exposure time to the plasma species. The experimental data indicates that the initial reaction probability depends on the functional groups present in the polymer for both atomic oxygen and molecular fluorine attack. Molecular oxygen did not react with any polymers. Polymers containing aromatic functional groups reacted faster with the gas-phase species than polymers containing carbonyl groups. For the reaction of the polymers with an oxygen plasma, production of surface carbonyl and carboxylic acid groups was favored over the formation of surface alcohol species. For the reaction of the polymers with molecular fluorine, formation of surface CF1 species dominated in aromatic containing polymers. The dependence on the functional group was also evident at long reaction times. The effect was most prevalent for the reaction of molecular fluorine with the polymer samples, where the fluorine to carbon ratio for aromatic polymers was more than twice that of a carbonyl containing polymer. Fluorine plasmas were so reactive with all polymers that the effect of the polymer functional group could not be determined. The reaction of the polymers with a fluorine plasma resulted in the formation of surface CF2 species.