Influence of edge gradient on morphology of edge roughness using PMMA

The edge roughness of lithographically defined resist features is an important aspect of micro fabrication of semiconductor devices. Previous work has demonstrated origin of line edge roughness due to polymer phase separation during the development step; effect of developer composition, type and development method on roughness and also the correlation of surface roughness with edge roughness in poly(methylmethacrylate) PMMA. In this work the influence of edge gradient on the morphology of edge roughness is presented using PMMA resist and atomic force microscopy (AFM) technique. Since for very steep edges, the AFM technique is unable to image the resist roughness close to the substrate due to shadowing by the higher parts of the resist. Features were defined lithographically by controlling the change in dose at the feature edge, allowing the edge roughness and its corresponding morphology for steep features to be determined by extrapolation from AFM measurements of relatively shallow exposure gradients.