Disturbance force observer for a wafer positioning system for immersion lithography

Abstract

In immersion lithography, the wafer on the chuck is immersed by the immersion hood. Interaction of the chuck with the immersion hood leads to a position disturbance on the wafer. Three disturbance observers are designed with the aim for immersion hood disturbance compensation: An inverse rigid-body plant based observer, a Kalman observer and an H infinity observer. First a model of the wafer positioning system with immersion hood is built. Then the observers are designed using this model. After that, the observers are analyzed using Bode plots and a gutter disturbance simulation. Finally, the observers are tested for applicability on a wafer scanner. Theoretically, the Kalman and H-infinity observers can estimate a 1 degree of freedom immersion hood disturbance force on a full model of the wafer positioning system. The inverse rigid-body plant based observer can estimate a multiple degree of freedom disturbance force on a rigid body model of the wafer positioning system. Experiments showed that a multiple degree of freedom disturbance estimation is needed for accurate compensation and that online compensation is required due to varying gutter disturbance. Future work must be focused on stable, online high bandwidth compensation using a multiple degree of freedom disturbance observer.

Date of Award	31 Dec 2013
Original language	English
Supervisor	Hans Butler (Supervisor 1) & Wilbert Simons (External coach)