Abstract: A method of measuring distortion for an exposure apparatus is disclosed and comprises; aligning a reticle comprising a plurality of measuring patterns over a first wafer, wherein the plurality of measuring patterns are separated by a first pitch in a first direction and a second pitch in a second direction orthogonal to the first direction, forming a plurality of first exposure patterns on the first wafer by performing a first exposure process through the reticle, shifting the reticle by a first distance from a position at which the first exposure process was performed and aligning the reticle over the first wafer, forming a plurality of second exposure patterns on the first wafer by performing a second exposure process through the reticle, aligning the reticle over a second wafer, forming a plurality of third exposure patterns on the second wafer by performing a third exposure process though the reticle, shifting the reticle by a second distance from a position where the third exposure process was performed

Abstract: An auto focus system includes a stage on which a substrate is mounted, light sources that irradiate the substrate with a plurality of focus beams directed towards the substrate at different angles, sensors that detect the focus beams reflected from the substrate, and a controller that determines the relative location of a surface of the substrate according to the locations at which the focus beams are detected by the sensors and positions the substrate accordingly. To this end, the controller performs calculations that are free from the influence of variations in the refractive index of the medium through which the focus beams propagate to the surface of the substrate. Therefore, the autofocus process is carried out with a high degree of precision.

Abstract: Interferometer systems for measuring displacement include a displacement interferometer. This interferometer includes a displacement converter responsive to a measuring beam of light. The displacement converter is configured to transform movement thereof in a direction orthogonal to the measuring beam of light into a change in path length between a reflective surface of the displacement converter and the measuring beam of light. The displacement converter may include a transmission grating and a displacement mirror or a reflecting grating.