Overlay measurment device

An overlay measurement device for measuring an error between a first overlay mark and a second overlay mark respectively formed on different layers formed on a wafer, comprising:

• a light source;
• a first beam splitter configured to split a beam emitted from the light source into a first beam and a second beam;
• a first color filter configured to adjust a first center wavelength and a first band width of the first beam so that the first center wavelength and the first band width of the first beam become suitable for acquiring an image of the first overlay mark;
• a second color filter configured to adjust a second center wavelength and a second band width of the second beam of the two beams split by the first beam splitter so that the second center wavelength and the second band width of the second beam become suitable for acquiring an image of the second overlay mark;
• a beam combiner configured to combine the first beam and the second beam;
• an objective lens configured to condense a beam combined by the beam combiner at a measurement position on the wafer and collect a beam reflected from the measurement position, wherein the first center wavelength and the first band width of the first beam are suitable for acquiring the image of the first overlay mark in the beam combined by the beam combiner and in the beam reflected from the measurement position and collected by the objective lens, and the second center wavelength and the second band width of the second beam are suitable for acquiring the image of the second overlay mark in the beam combined by the beam combiner and in the beam reflected from the measurement position and collected by the objective lens;
• a second beam splitter configured to split the beam reflected from the measurement position and collected by the objective lens into a third beam having the first center wavelength and the first band width and a fourth beam having the second center wavelength and the second band width;
• a first detector configured to acquire the image of the second overlay mark by detecting the third beam having the first center wavelength and the first band width;
• a second detector configured to acquire the image of the first overlay mark by detecting the fourth beam having the second center wavelength and the second band width;
• a third beam splitter configured to split the beam passed through the beam combiner into two beams;
• and
• a beam detector configured to analyze an optical property of one of the beams split by the third beam splitter,
• wherein the other of the beams split by the third beam splitter is directed toward the objective lens, and the other of the beams is condensed at a measurement position on the wafer by the objective lens.