ROBUST SUBPIXEL ALIGNMENT IN LITHOGRAPHY

Lithographic alignment is the problem of estimating the position of a feature that has previously been etched onto a wafer. Ideally, the alignment algorithm should be accurate without being computationally complex. In this article we describe an algorithm that, for symmetric pulses, achieves the accuracy of correlation at a fraction of the computational expense. The algorithm will automatically adapt to the minimum error condition for an unknown mark. We show that this algorithm is more robust than simple edge detection.