Wafer chuck with integrated reference sample

A wafer translation stage for use in an optical metrology tool that permits the location of a reference sample within the stage area utilized for wafer metrology thereby reducing the required translation range comprising:

• a vacuum-chuck for holding and locating a wafer at a measurement position;
• a wafer motion system coupled to the chuck for translating a wafer said wafer motion system including at least two elements selected from the group consisting of linear-translation and rotary stages;
• a holder supporting a reference sample, said holder being located within the body of the vacuum-chuck at a location within the stage area utilized for wafer metrology, said holder being movable between a retracted position where the reference sample is below the vacuum-chuck surface and an extended position where the reference sample is raised to be co-planar with the wafer measurement position, said holder comprising:
• a piston having a support surface for a reference sample located within and free to move within a housing, said housing containing locating surfaces that limit the range of the piston motion and establish the retracted and extended positions;
• a member fixed to the surface of the piston said member forming a hydraulic seal between the piston and housing thereby dividing the housing into upper and lower hydraulic chambers and enabling hydraulic actuation of the piston by differential pressurization of said upper and lower hydraulic chambers;
• and
• a hydro-mechanical actuation mechanism for moving the piston between the extended and retracted position, said actuation mechanism comprising:
• a conduit connecting the upper hydraulic chamber to the surface of the vacuum-chuck;
• a spring arranged to locate the piston in the retracted position in the absence of differential pressurization of the upper and lower hydraulic chambers and locate the piston in the extended position in the presence of differential pressurization of said upper and lower hydraulic chambers;
• a gas manifold that connects the lower hydraulic chamber and vacuum-chuck to both a source of pressurized gas and a vacuum system;
• and
• a check-valve arranged to inhibit differential pressurization of the upper and lower hydraulic chambers during manifold evacuation and enable differential pressurization of the upper and lower hydraulic chambers during manifold pressurization.

A wafer translation stage for use in an optical metrology tool that permits the location of a reference sample within the stage area utilized for wafer metrology thereby reducing the required translation range comprising:

• a vacuum-chuck for holding and locating a wafer at a measurement position;
• a wafer motion system coupled to the chuck for translating a wafer;
• a holder supporting a reference sample, said holder being located within the body of the vacuum-chuck at a location within the stage area utilized for wafer metrology, said holder being movable between a retracted position where the reference sample is below the vacuum-chuck surface and an extended position where the reference sample is raised to be co-planar with the wafer measurement position;
• a source of pressure in selective communication with the holder for biasing the holder into the extended position;
• and
• a spring for urging the holder back to the retracted position.