Sub-nanometer accurate fiber-fed heterodyne interferometer

IC-production processes are among the most demanding ones when it comes to high-precision positioning. For most systems performing long-range measurements, sub-micrometer resolutions and displacement accuracies over long strokes are common. Now the semiconductor industry pushes its demands to the extreme with the advent of Extreme Ultraviolet Lithography (EUV). Accelerations and velocities are high in these systems (120 m/s² for the reticle and 30 m/s² for the wafer stage), whereas the required position measurements have to be performed with resolutions and accuracies in the order of sub-nanometers over a measurement range of a few decimeters. Delft University of Technology (TU Delft) has introduced a new heterodyne interferometer concept using spatially separated optical input beams to address this challenge.