Multivariable feedback control design for high-precision wafer stage motion

Abstract Conventional PID-like SISO controllers are still the most common in industry, but with performance requirements becoming tighter there is a growing need for advanced controllers. For the positioning devices in IC-manufacturing, plant interaction is a major performance-limiting factor. MIMO control can be invoked to attack this problem. A practically feasible procedure is presented to design MIMO feedback controllers for electromechanical positioning devices, using H ∞ /μ techniques. Weighting filters are proposed to straightforwardly and effectively impose performance and uncertainty specifications. Experiments show that MIMO control can considerably improve upon the performance with multiloop SISO control. Some problems are highlighted that are important for industrial practice, but that lack a workable solution.

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