SMART DISC − application in an ASML wafer stepper

High-precision machines typically suffer from small, but annoying, badly damped vibrations. In case such a vibration problem can not be solved passively, a solution may be found in active vibration con-trol. In this respect, research at the Drebbel Institute is aimed at the development of a device called SMART DISC (SD). It is envisioned as an active structural element, consisting of a piezoelectric position actuator co-located with a piezoelectric force sensor, and control and amplifier electronics. As an industrial, three-dimensional test set-up for evaluation of the performance of SD’s, the lens support of an ASML wafer stepper has been chosen. By inserting SD’s in the lens support, and applying Integral Force Feedback control, the relative tilt of the lens relative to the main plate has been reduced by more than a factor 3. The absolute acceleration level of the top of the lens at its dominant resonance frequency has been successfully reduced to less than 10 % of the original level