INTERFEROMETRIC PLATE ALIGNMENT

摘要

A photolithographic camera includes a system to monitor the alignment of a substrate supported in the camera. The light beam used to align the substrate is split by a beam splitter and one portion passes along the optical axis to the substrate and the other portion passes along a reference path. The two portions are recombined at a reference plane to establish an interference pattern. A photographic image of the desired interference pattern is also located at the reference plane and any differences between the two patterns produces Moire fringes indicating misalignment of the substrate.