Dual servo planar motion stage using magnetic levitation technology

Abstract

Stage is a system that makes a specimen track desired positions in real time. There are many kinds of stage systems and their applications. The stage system for semiconductor process requires highest precision and accordingly highest complexity. The technological improvement of stages was expedited by the advancement of semiconductor industry. According to the roadmap of the semiconductor industry, it is time to develop a magnetic levitation stage with high speed and high precision. The main objective of this thesis is to propose, design and control a novel dual servo magnetic levitation planar motion stage which is fast, highly precision, easy to expand motion range and vacuum compatible. Dual servo mechanism, for the first time, is applied to maglev stage system. The coarse maglev planar motion stage has form of moving coils and stationary magnets. Voice coil motors(VCMs) for a fine stage are designed within limited size of space. The coarse stage and the fine stage are integrated then the dual servo stage is controlled with laser interferometers and capacitive sensors. The coarse stage of the novel dual servo maglev stage has form of a maglev planar motor and the fine stage is driven by VCMs. Conceptual design of the both stages are followed by the design specifications of the planar motor and the VCMs. Electromagnetism, heat transfer and kinetics of the fine stage are utilized to obtain mathematical models explaining the relationship between the design parameters and the design specifications. Based on those models, the design parameters are determined so that the fine coarse stage and the fine stage show optimal performances. Final designs are verified by FEM simulations before realization. Two sets of sensors are equipped to the dual servo stage. Six capacitive sensors are used to measure the relative position of the coarse stage to the fine stage. Three other capacitive sensors and three laser interferometers are used to measure the absolute position of the fine stage. The dual servo stage is controlled in the manner of master and slave. The fine stage, the master axis is controlled to follow main command and the coarse stage, the slave axis, is controlled to follow the fine stage. Each stage is considered as six SISO systems by decoupling using model based kinematics and sensor transformation. Data acquisition boards, power supplies, current amplifiers and a controller embedding simple PID control algorithm are implemented and the performance of the dual servo stage is evaluated. The stage shows maximum speed of 100 mm/s and in-position stability of 10 nm which is highest level of precision ever. The dual servo stage should be improved to be in practical use but this thesis can give a contribution as a ground work for the next generation semiconductor lithography process.