US Patent 12066322 Single grab overlay measurement of tall targets

An overlay metrology system may include an objective lens, illumination optics to illuminate an overlay target including a first grating with a first pitch on a first sample layer and a second grating with a second pitch on a second sample layer, where the first and second sample layers are separated by a layer separation distance greater than a depth of field of the objective lens. The system may further include collection optics with a radially-varying defocus distribution to compensate for the layer separation distance such that the first and second gratings are simultaneously in focus on the detector.