a distance measurement method includes imaging a first light source emitting a first wavelength , on a region of a substrate with a dispersive confocal lens ; imaging a second light source emitting a second wavelength with the dispersive confocal lens on the region of the substrate ; measuring intensity of light reflection emitted from the first light source ; measuring intensity of light reflection emitted from the second light source ; and generating a first response function wherein the first response function represents reflected light intensity emitted from the first light source as a function of the distance .