Correction of Critical Dimension Uniformity on a Wafer by Controlling Back-Surface Transmittance Distribution of a Photomask

概要

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We report on a new method for correcting the critical dimension (CD) uniformity on a wafer, using a transmittance-controlled photomask with phase patterns on the back. Theoretical analysis of changes in the illumination-pupil shape with respect to the variation of the size and density of the back-surface 180°-phase contact-hole patterns and experimental results using the transmittance-controlled photomask are presented. It is shown that pattern size on the back of the photomask must be made as small as possible in order to keep the illumination-pupil shape as close as possible to the original one and to achieve as large an illumination intensity drop as possible at the same pattern density. It is demonstrated that the method is very effective for correcting the CD nonuniformity on a wafer that is induced by both CD nonuniformity of the photomask and flare in the exposure tool.
2004-09-15