An apparatus for detecting a mark on a substrate is provided. The mark has a first stripe group and a second stripe group disposed in parallel to each other. The apparatus includes a detection module operative to move over a surface of the substrate. The detection module includes a detection unit for obtaining data from the mark and operative to perform repeated acquisition operations on the first stripe group and the second stripe group of the mark. Each of the acquisition operations acquires data associated with the first stripe group or the second stripe group of the mark. The detection module also includes a positioning unit for aligning the detection unit with the mark.