The Rotational Stage is a 2-axle, numeric controlled machine table between the top and bottom of the measuring instruments that moves the wafer in polar coordinate direction.
Its large aperture enables full access to a 300 mm wafer from the bottom side. Instead of a vacuum chuck it is equipped with convertible inlays. They assure that the wafer is hold down from the bottom side with a minimum of masking.
Typical metrology applications for a rotational stage are: fast spiral scans of the wafer to generate full wafer maps of layer thickness, thin-film thickness and total wafer thickness within minutes.