Line Width Variation due to Global Topography

To obtain the spun-on resist surface profile around a topographical feature, the analytical solution of an equation derived from mass continuity and the Navier-Stokes equation using the lubrication approximation was used. The final resist thickness profile was obtained by applying our previous experimental result of resist thickness reduction due to the soft bake process. We found that the difference in resist thickness could induce severe critical dimension variation. Since the resist height differences between above and far from the feature could be greater than the focus margin, a 180 nm line and space pattern could not be obtained for the entire area within the process latitude. To overcome this problem, we applied mask bias and an edge phase-shift mask. As a result, the desired line and space pattern was obtained for the entire global topographical area.