Patent attributes
An interferometric overlay tool may include an interferometer and a controller. The interferometer may include one or more beamsplitters to split illumination including one or more wavelengths into a probe beam along a probe path and a reference beam along a reference path, one or more illumination optics to illuminate a grating-over-grating structure with the probe beam, one or more collection optics to collect a measurement beam from the grating-over-grating structure, one or more beam combiners to combine the measurement beam and the reference beam as an interference beam, and a variable phase delay configured to vary an optical path difference (OPD) in the interferometer. The controller may receive one or more interference signals representative of interferometric phase data associated with a plurality of OPD values and the one or more wavelengths from a detector and determine an overlay error of the grating-over-grating structure based on the interferometric phase data.
