This paper proposes a focusing and leveling technique for optical lithography tools using linear CCD and image
processing method. A double telecentric optical system is designed, which projects an aperture onto the surface of the
wafer at a large incident angle, and then the reflected beam results in a spot image onto a linear CCD. A mathematical
model relating the spot lateral displacement to the change of wafer height is established. Two image processing
algorithms for displacement detection of the spot image measured by the linear CCD are also proposed. A lot of
experiments including the system calibration conducted on a test rig confirm that the proposed technique is feasible and
effective. The repetitive height measurement accuracy of the system is verified to be more than 200 nm within a wide
band measurement range of 1 mm.