Beam steering system and spatial filtering applied to interference lithography

Abstract

Production of metrologically accurate interference patterns with subnanometer fidelity requires precise control of beam position and angle. We consider the beam stability requirements for the cases of interference by plane and spherical waves. Interferometers using beamsplitter cubes and diffraction gratings are among the analyzed topologies. The limitations of spatial filtering to remove angular variations are also discussed. We present a beam steering system that uses position sensing detectors, tip-tilt actuators, and digital control to lock the beam position and angle at the interference lithography system. We describe the prototype’s performance and limitations of this approach. This beam steering system allows us to locate the laser far (∼10 m) from the sensor assembly, thereby reducing the thermal and mechanical disturbances at the lithography station and allowing sharing of the laser between different lithography tools.