Control-relevant Identification and Robust Motion Control of a Wafer Stage

Abstract

This chapter illustrates the identification of control-relevant models and the subsequent robust control design applied to a wafer stage. A wafer stage is part of a wafer stepper and used in chip manufacturing processes for accurate positioning of the silicon wafer on which the chips are to be produced. Accurate and fast positioning requires a robust and high-performance multivariable servo controller that enables a fast throughput of silicon wafers. An advanced servo controller is developed by an iterative procedure of control-relevant model identification including model uncertainty bounding, and robust control based on worst-case performance optimisation. Both stability and performance robustness can be monitored, enabling the possibility of guaranteeing performance improvement in a single step of the iteration. This is shown to lead to a successful design and implementation on a wafer stage set-up.