Ultra-precision Wafer Positioning by Six-axis Micro-motion Mechanism

This paper discusses an ultra -precision wafer positioning technique, especially applicable to improve the alignment accuracy of X-ray lithography systems. A unique six axis micromotion mechanism using high resolution piezoelectric actuators has been developed, and its kinematic characteristics and micro-positioning performance have been thoroughly investigated. As to the structure of the mechanism, a wafer chuck is supported by six links comprised of piezoelectric actuator and spherical metal joints at both ends, which enable the chuck to move with respect to six degrees of freedom by expanding and contracting the links. To improve design versatility of position control systems, a software (digital) servo control featuring variable voltage integration has been introduced. The experimental results indicate that this technique is capable of positioning the wafer with a resolution less than 0.01μm.