| 摘要 |
PURPOSE:To eliminate the gap amount setting up process before detecting the positional slip of a mask and a wafer by a method wherein laser beams in a plurality of wavelengths are simultaneously used while the diffraction light intensity conforming to the fluctuation in gap amount is made contact. CONSTITUTION:A mask 1 and a wafer 2 are arranged in parallel with each other and then a linear Fresnel zone plate LFZP 3 is provided on the mask 1 while a diffraction gratings 4 are provided on the wafer 2. Next, laser beams in a plurality of wavelengths are decomposed into respective components of the wavelengths by dichronic mirrors 16a-16c to equalize the wavelength intensity through ND filters 17a-17c. These laser beams focussed by the other dichronic mirrors 18a-18c irradiate the LFZp 3 to detect the reflected diffraction light from the diffraction gratings 4. Through these procedures, the diffraction light intensity can be made constant extending over wide range by simultaneously using the laser beams in multiple wavelengths. |
