Investigation of pupil-fill factors as process window indicators for dry optical lithography

This work presents two pupil-fill factors as process window indicators for optical projection lithography when resolution enhancement techniques are employed. The formulations of these two pupil-fill factors are based on two different concepts of the correlation between the process window and the diffraction orders captured at the pupil of the imaging lens. One pupil-fill factor considers the amplitude of the diffracted orders. The other pupil-fill factor considers the extent of overlap between the 0th and the 1st diffraction orders at the pupil. This work investigates how accurately the variation of the two pupil-fill factors indicates the influences of source configuration and mask features on the process window. The Chromeless Phase Shift Lithography (CPLTM) technology, in the context of dry optical lithography, is used as a case study. The results suggest that the pupil-fill factor, which considers the amplitude of the diffraction spectrum, is a better process window indicator than the other. (c) 2007 Elsevier Ltd. All rights reserved.