| 摘要 |
PURPOSE:To measure a gap during exposure by providing a linear Fresnel zone plate (LFZP) whose focal length is varied continuously on a mask and scanning laser light on it. CONSTITUTION:The continuously variable LFZP 2 whose focal length is varied continuously is provided on a mask 1 and a diffraction grating 4 is provided on a wafer 3 facing the mask 1. Then, a parallel laser beam 5 is scanned on the LFZP 2 and reflected and diffracted light from the grating 4 is detected. At this time, the beam 5 incident on the LFZP 2 is diffracted and converged by the LFZP 2, reflected and diffracted by the grating 4, and returned to the LFZP 2. Then when the focal length of the LFZP 2 on which the beam 5 is incident becomes equal to the gap quantity between the mask 1 and wafer 3, the beam 5 passed through the LFZP 2 is rechanged into a parallel beam and the output of a detector becomes maximum. The gap quantity between the mask 1 and wafer 3 is measured from the incidence position of the beam 5 where the output of the detector becomes maximum. |
