Robust design of a novel three-axis fine stage for precision positioning in lithography

The precision positioning system for semiconductor lithography requires a robust structural design to obtain enough control bandwidth and an efficient actuator with fast access time. In this article, a three-axis stage is proposed as a fine stage of a dual stage for the precision positioning. Its actuators are voice coil motors (VCMs) whose coil windings are mounted on the coarse stage and its magnets are on the fine stage. Between the fine and coarse stages, there is no mechanical connection but only magnetic coupling. The eight pairs of magnets and four coil windings are arrayed symmetrically. The three-axis stage's dynamic characteristics are improved by enhancing the actuating force and modifying its own structure using finite-element analysis in order to meet its requirements of high bandwidth and large forces. The actuating force is strengthened by modifying each VCM's magnetic circuit. The structure is designed to be robust by using design of experiment (DOE) as well. The modified stage is verified to have enough dynamic characteristics through experiments.