Polymer diffusion as a probe of damage in ion or plasma etching

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Abstract
Dry etching of polystyrene (PS) with oxygen, using ion beams or plasmas is found to affect the diffusioncharacteristics of molten PS. Four different techniques, reactive ion beametching (RIBE), reactive ion etching (RIE), and plasma etching in barrel and downstream reactors are used. Polymer molecules lying near the surface of an etched sample are found to have been immobilized, and thus unable to diffuse. The quantity of material affected in this manner is found to increase with polymer molecular weight, and to be greater in samples etched by RIBE and RIE than in the pure plasma methods. Etching is also found to reduce the permeability of the sample surface to diffusion by unetched polymers. The permeability is found to decrease with the penetrant polymer’s molecular weight, and to decrease more drastically in RIBE and RIE treated samples than the plasmatreated samples. Surface wrinkling of RIBE samples upon annealing above the glass transition temperature is also seen. The results are found to yield a consistent picture of polymer damage during dry etching consisting of crosslinking and chain scission. These experiments demonstrate the utility of polymerdiffusion in the characterization of topological damage to polymer molecules.