Abstract: The 'edge detection' is a known problem in optical linewidth metrology. New illumination capabilities like Real Time Broad Band Confocal Scanning, the combination of conventional transmitted illumination with real time confocal scanning, and near UV transmitted illumination, used for metrology of finite transmissive/reflective masks, require a reevaluation of the traditional edge detection approach. For the masks with finite reflectivities or transmission on both sides of an edge the traditional 50% threshold does not describe at all the true edge location. Edge response function and Edge response width were reviewed for confocal scanning illumination and for typical finite transmissive (binary) masks. The proposed edge detection strategy deals with edge position shift with detection threshold in different illumination conditions and the relationship between the detection threshold and 'best' focal plane selected for measurement. 'Edge roughness', another known problem was reviewed from different prospectives and measurements of the edge roughness were performed at various edge detection thresholds. Mapping of mask feature 'aerial intensity' was used to view the edge roughness, edge slope and to locate edge position. Aerial intensity simulations with SOLID-C simulation tool were in very good agreement with the experimental data.!6
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