Evolution of roughness on photoresist (PR) sidewalls during PR trim etching has been investigated using an integrated two-dimensional plasma equipment-feature evolution model. Results show that the PR trim process reduces PR surface roughness as exposure to energetic ions enhances etching of "rough" protrusions while shadowing of neutral etchants within rough cavities reduces the etch rate there. Large amplitude roughness is found to be relatively easier to remove so the roughness reduction rate decreases as the trim etch process progresses. This is because the disparity between the etch rate of rough protrusions and cavities decreases as roughness is reduced and all regions of the surface start etching laterally at similar rates. Low spatial frequency roughness components are more difficult to remove during PR trimming than high-frequency components because,there is less neutral etchant shadowing within cavities at low frequencies and rough bumps become too broad to effectively remove through physical sputtering. (C) 2003 American Vacuum Society.