Evaluation of Straightness of Two-Axes Stage

Abstract

Two-axes stages (XY stage) are used for precise machining and precise positioning. The XY stage should have the resolution of nanometer in the nanotechonology. In order to determine that the XY stage has enough small resolution, it is necessary to evaluate the positioning accuracy. The shape of stage axes affects measurement result. Therefore, it is necessary to know the shape of the axes. This paper describes the method how to evaluate the straightness of the stage to measure the behavior of the stage. The behavior of the stage is measured by laser interferometer, which measures the displacement. The reflection mirrors are set up on the stage, which reflects the laser. The result of measurement by the laser interferometer includes both of the shape of the reflection mirrors and the shape of the axes. In the case of nanometer positioning, the shape of the reflection mirrors affects measurement result, as the profile error of reflection mirrors are as small as motion error. We theoretically and experimentally inspect whether both errors can be separated from the displacement. In this simulation, the shape of axes and the shape of the reflection mirrors are generated randomly. The shape of axes and the shape of reflection mirrors are estimated by non-linear least-squares method. The estimated shape of axes and shape of reflection mirrors are compared with the ideal shape of them. After simulation, similar method is applied to the actual stage and laser interferometer. The result of simulation and measurement are shown.