A Look at Overlay Error

摘要

A trend toward mix-and-match lithography schemes is running head to head with tighter overlay requirements, calling for greater overlay control, increased analysis and understanding of overlay errors. The main contributors to overlay error are the stage, alignment system and distortion signature. Errors can be broken down into stage motion or wafer alignment errors such as placement and rotation inaccuracies and field errors like errors on the reticle and in camera magnification. These errors are correctable. Pincushion or barrel distortions, third-order field errors, are not correctable but are routinely characterized for a given exposure tool.