Model polymer etching and surface modification by a time modulated RF plasma jet: Role of atomic oxygen and water vapor

The surface interaction of a well-characterized time modulated radio frequency (RF) plasma jet with polystyrene, poly(methyl methacrylate) and poly(vinyl alcohol) as model polymers is investigated. The RF plasma jet shows fast polymer etching but mild chemical modification with a characteristic carbonate ester and NO formation on the etched surface. By varying the plasma treatment conditions including feed gas composition, environment gaseous composition, and treatment distance, we find that short lived species, especially atomic O for Ar/1% O₂ and 1% air plasma and OH for Ar/1% H₂O plasma, play an essential role for polymer etching. For O₂ containing plasma, we find that atomic O initiates polymer etching and the etching depth mirrors the measured decay of O atoms in the gas phase as the nozzle-surface distance increases. The etching reaction probability of an O atom ranging from 10^-4 to 10^-3 is consistent with low pressure plasma research. We also find that adding O₂ and H₂O simultaneously into Ar feed gas quenches polymer etching compared to adding them separately which suggests the reduction of O and OH density in Ar/O₂/H₂O plasma.