Polymer aggregates in a photoresist layer may be dissolved or reduced in dimension by treatment with supercritical carbon dioxide. The supercritical carbon dioxide may be used before and/or after development of the photoresist. The SCCO₂ treatment causes swelling of the photoresist and may allow polymer aggregates in the photoresist to be dissolved. Controlled release of the carbon dioxide de-swells the photoresist, resulting in reduced line edge roughness of openings in the photoresist and reduced resistance of metal lines formed in the openings.