A method of measuring the motion of a stage has been developed based on a Thru The Lens optics system. Images of the target, which has line space patterns written on a Si wafer, are detected through the lens by a linear image sensor, which is synchronized with the output of the position sensor of the scanning stage. The displacement from the ideal orbit is measured by an image analysis method. This method has a fixed measuring point in contrast with the moving measuring point of a laser interferometer system, and the method is optimum for laser processing systems and LSI wafer inspection systems. Its accuracy was evaluated to be 10 nm p-p.
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