Abstract: A method of centering a correlation-based overlay includes resizing an overlay target image to a size smaller than an entire image size, defining first and second templates that are symmetrical to each other based on a diagonal in the resized image, and calculating a rough center coordinate by calculating a first correlation value representing a similarity symmetrical with respect to the diagonal between images of the first and second templates; defining first and second templates symmetrical based on a diagonal passing through the rough center coordinates in an original image of the overlay target image, calculating a fine center coordinate of the overlay target image by calculating a second correlation value representing a similarity symmetrical with respect to the diagonal between the images of the first and second templates; and centering an overlay key by moving a stage to a target position based on the fine center coordinates.