Halation reduction for single-layer DUV resist processing

In order to apply single layer resist processing to 0.25-micrometer patterning, the effect of topography was studied in KrF excimer laser lithography, using a two-dimensional resist profile simulator with vector model. In particular, we simulated resist transmittance dependence on depth of focus (DOF) and halation, by considering a conventional (non- bleaching type) DUV chemically amplified positive resist. Here, we varied the step angle of the topographic substrate (height 0.1 micrometer) and the distance between step and resist pattern. Moreover, we investigated the influence of two optical resist characteristics, photo- bleaching and photo-coloring, from the viewpoint of halation reduction. For a highly reflective substrate such as polysilicon, the optimum transmittance (DOF greater than or equal to 1.0 micrometer) of the non-bleaching type resist with a resist thickness of 0.7 micrometer was determined to be 40 - 50%. In such a non-bleaching type resist, a good profile was obtained when the distance between the step and the resist pattern edge was more than 0.3 micrometers. Moreover, it was found that photo-coloring in the resist film was effective for halation reduction.