An X-Y Stage with a Plane Cross Grating Metrology System

Abstract

This paper describes an X-Y stage with a plane cross grating for position feedback. The stage has a current servo motor and a piezoelectric actuator to realize coarse and fine positioning throughout the 50mm x 50mm range of travel. The objective table contacts tightly on a planar wafer to enhance the motion flatness. The horizontal positioning noise is less than 20nm. The stage has a positioning accuracy of 3µm. If a high quality grating and guide is used, it should be useful for 3D surface measurement and ultra-precision machining. The operating principle and the characteristics of the plane cross grating are presented. The internal structure is explained. The comparison result for the stage with a laser interference calibration is presented. The theoretical precision and error sources of the system including grating grid, guide and grating installation error are analyzed. Experiments on factors such as system noise, guide error and motion interference are presented and the results are analyzed.