Multi-channel grating interference alignment sensor

摘要

An alignment sensor having a fixed reference grating and a movable wafer grating receiving electromagnetic radiation from a coherent illumination source. The illumination source is split into two beams by a beamsplitter. One beam is directed to a fixed reference grating and the diffracted orders are collected. The other beam from the beamsplitter is directed to a movable wafer grating. The diffracted orders from the movable wafer grating are collected and caused to interfere with the diffracted orders from the fixed reference grating, causing a phase shift indicative of the wafer movement or misalignment with respect to the fixed reference grating. Multiple channels having discrete wavelengths or colors are used to optimize detection and alignment irrespective of wafer processing variables. A polarization fixture on the illumination source and a central polarizing portion on the beamsplitter is used to provide contrast optimization, or alternately a latent image metrology mode. The alignment sensor improves alignment accuracy irrespective of processing variables and provides flexibility improving efficiency in the manufacture of semiconductor devices.