A method for patterning a substrate with reduced defectivity is described. Once a pattern is formed in a layer of radiation-sensitive material using lithographic techniques, the pattern formed on the substrate is post-treated. The post-treating of the pattern in the layer of radiation-sensitive material is performed to reduce a roughness of the pattern. The post-treating includes performing a treatment process on the pattern to alter a solubility of an exposed surface of the pattern, wherein the treatment process involves performing a first chemical treatment of the pattern using a liquid-phase chemical solution containing a first surfactant, or exposing said pattern to second EM radiation different than said first EM radiation. Following the treatment process, the post-treating includes hard baking the pattern, and performing a second chemical treatment of the pattern using a vapor-phase chemical solution to reduce the roughness.