Patent ID: 6832517
Filing Date: 2004-12-21
Classification: G01B,G01C,G01S

Abstract:
A system for monitoring position of a reticle's top surface, the system comprising:a reticle stage having a reticle holding well for holding the reticle in place; a reference plane defining the position of the reticle's top surface when the reticle is properly level in the reticle stage, the reference plane having associated therewith an incidence axis and a reference reflection axis; at least one optical level detector mounted on the reticle stage comprising a set of connecting hardware for adjusting the height of the optical level detector relative to the reticle's top surface wherein the at least one optical level detector is positioned over the reticle holding well, each of the at least one optical level detector comprising: a light source for projecting an incidence beam of light toward the reticle's top surface along the incidence axis, wherein when the reticle's top surface is in same position as the reference plane, the incidence beam of light is reflected by the reticle's top surface into a reflected beam that is coincident with the reference reflection axis; and a reflector for deflecting the reflected beam toward a light detector along the light detector's viewing axis and fully registers with the light detector, causing the light detector to generate a first signal value and when the planar surface's position is deviated from the reference plane, the reflected beam does not fully register with the light detector, causing the light detector to generate a second output signal value; wherein the at least one optical level detector is used to monitor position of the reticle's top surface in relation to the reference plane by monitoring the output signal value of the optical level detector's light detector.