Abstract: Pattern-dependent random deviations in measurement of optimal focus distances can be minimized by separating scan paths into multiple types of scan paths that scan only a respective predetermined image region in semiconductor dies. A substrate including in-process semiconductor dies is coated with a photoresist layer, and is located onto a stage in a lithographic exposure tool. Maps of optimal focus distances are generated by performing optimal focus distance scans that cover a respective subset of image regions having distinct image patterns. The substrate can be leveled with respect to an optics system of the lithographic exposure tool employing a weighted average of multiple maps of optimal focus distances. Once the substrate is leveled on the stage, a lithographic exposure process can be performed with enhanced uniformity in the focus distances across the in-process semiconductor dies.