<title>Pattern Recognition Automatic Fine Alignment</title>

Abstract

As alignment tolerances and the associated overlay characteristics become more important to microlithography, automatic alignment has proven to be necessary for high yields and consistent throughput. This paper describes an Automatic Alignment System designed for, but not limited to, projection printers. In this scheme a vidicon is used to detect the images projected from special targets on the mask and wafer. The video information is procesed by a microcomputer system that performs a pattern recognition algorithm to determine target position and the necessary alignment correction. The system closely resembles operator alignment in concept, yet gives greater accuracy and more consistent performance. Operational principles and actual performance are discussed.