Lithographic apparatus and a method to compensate for the effect of disturbances on the projection system of a lithographic apparatus

Abstract

Embodiments of the invention provide a lithographic apparatus including an illumination system configured to condition a radiation beam, a patterning device support constructed to support a patterning device, the patterning device being capable of imparting the radiation beam with a pattern in its cross-section to form a patterned radiation beam, a substrate table constructed to hold a substrate, a projection system configured to project the patterned radiation beam onto a target portion of the substrate, an active air mount to support the projection system, the active air mount including at least one actuator, and a feed-forward device, the feed-forward device being configured to provide on the basis of a set-point signal of a movable object, a feed-forward signal to the at least one actuator, wherein the feed-forward signal is designed to decrease a disturbance effect on the projection system due to movement of the movable object.