US Patent 7301623 Transferring, buffering and measuring a substrate in a metrology system

A chuck that clamps a substrate to the top surface using, e.g., a vacuum, electrostatic force, or other appropriate means, includes a plurality of lift pins that can raise the substrate off the top surface of the chuck. The chuck may be used with a metrology device that measures the substrate using a first type of measurement, e.g., film thickness measurement, while the substrate is held flat, and measures the substrate using a second type of measurement, e.g., radius of curvature measurement, while the substrate is supported on the lift pins. The thickness and radius of curvature measurements may then be used to determine the stress on the substrate. The lift pins may include an aperture through which a vacuum is applied through the top surface of the lift pins to the bottom of the substrate to securely hold the substrate while moving.