Influence of developer and proximity effect on morphology of edge roughness in lithographically graded exposures 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; influence of edge gradient on the morphology of edge roughness; effect of development technique and developer on surface roughness of large area features and also the correlation of surface roughness with edge roughness in poly(methylmethacrylate) PMMA. In this work the influence of developer and proximity effect on morphology of edge roughness in lithographically graded exposures using PMMA resist and atomic force microscopy (AFM) technique is investigated. 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.