The Functional Relation between Alignment Accuracy and Vertical Separation of Alignment Marks

Abstract
The purpose of this study was to determine the functional relation between alignment error (horizontal offset of two alignment marks) and the vertical separation distance of the alignment marks when the alignment is attempted. This relation was studied with four types of alignment marks and two extreme levels of ambient illumination. The vertical separations ranged from 0.050 to 3.2 in. A significant interaction was found between vertical separation distance and alignment mark design: designs which provided vernier cues were found to be the most effective at greater vertical separation distances. The relation between alignment error and vertical separation can be described by a third-order polynomial.

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