Overlay measurement apparatus and overlay measurement method

An overlay measurement apparatus comprising:

• a light source configured to direct light to a plurality of overlay targets formed on a wafer;
• a lens unit including:
• an objective lens configured to focus the light on a measurement position of one of the plurality of overlay targets;
• and
• a lens focus actuator configured to adjust a distance between the objective lens and a surface of the wafer at the measurement position;
• a detector configured to acquire a focus image at the measurement position based on a beam reflected from the measurement position;
• a stage on which the wafer is seated;
• and
• a controller configured to:
• control the lens unit, the detector, and the stage to measure a preset collection-purposed overlay target among the plurality of overlay targets, the collection-purposed overlay target being used to generate the correction value;
• collect a target coordinate of the collection-purposed overlay target spaced apart from a center of a field of view (FOV) of the lens unit;
• calculate a correction value based on the target coordinate;
• move the stage under application of the correction value;
• and
• control the lens unit, the detector, and the stage to measure at least one application-purposed overlay target among the plurality of overlay targets, after application of the correction value to movement of the stage,
• wherein the controller includes:
• a stage actuator configured to control the movement of the stage;
• a storage for storing therein an image of the collection-purposed overlay target and an image of the application-purposed overlay target obtained using the detector;
• an offset calculator configured to calculate a distance between the target coordinate of the collection-purposed overlay target and the center of the field of view of the lens unit;
• and
• a correction value calculator configured to calculate the correction value based on the target coordinate,
• wherein the correction value calculator is configured to calculate the correction value using distances between a plurality of the target coordinates repeatedly measured by the detector and the center of the field of view of the lens unit.