Multivariable feedback relevant system identification of a wafer stepper system

This paper discusses the approximate and feedback relevant parametric ident ification of a positioning mechanism present in a wafer stepper. The positi oning mechanism in a wafer stepper is used in chip manufacturing processes for accurate positioning of the silicon wafer on which the chips are to be produced, The accurate positioning requires a robust and high-performance f eedback controller that enables a fast throughput of silicon wafers. A cont rol relevant set of multivariable finite dimensional linear time invariant discrete-time models is formulated and estimated on the basis of closed-loo p experiments. The set of models is shown to be suitable for model-based ro bust control design of the positioning mechanism; this is illustrated by a successful design and implementation of a robust controller.