Patent ID: 6043892
Filing Date: 2000-03-28
Classification: G03F

Abstract:
An apparatus for detecting deviation of a surface from a reference plane, said apparatus comprising:a leveling stage for supporting a surface to be exposed;a plurality of support members supporting said leveling stage so as to allow the stage to be tilted relative to the horizontal;a stage driver, disposed at one side of said leveling stage, which tilts said leveling stage relative to the horizontal;a light source which outputs light directed toward the upper surface of the leveling stage at an acute angle relative to the horizontal so as to irradiate an exposure field of a surface supported on the stage;a detector which receives the light once the light has reflected from the exposure field and determines whether the exposure field is inclined relative to the horizontal;an aperture which alters at least one dimension of the beam of light from said light source before the light is incident on the detector; andmeans for moving the aperture between a first location at which the aperture is disposed out of the path of the beam of light such that no aperture is in the path of the beam of light and a second location at which the aperture is disposed in the path of the beam of light.