Abstract: In a lithographic projection apparatus the positions and/or orientations of reflective optical elements is dynamically controlled. The position of a reflective optical element such as a mirror in an illumination or projection system is first measured using an absolute position sensor mounted on a reference frame and thereafter measured by a relative position sensor also mounted on said reference frame. The position of the element is controlled in accordance with the measured position, e.g. to maintain it stationary in spite of vibrations that might otherwise disturb it. The absolute sensor may be a capacitive or inductive sensor and the relative sensor may be an interferometer.

Abstract: In a lithographic projection apparatus the positions and/or orientations of reflective optical elements is dynamically controlled. The position of a reflective optical element such as a mirror in an illumination or projection system is first measured using an absolute position sensor mounted on a reference frame and thereafter measured by a relative position sensor also mounted on said reference frame. The position of the element is controlled in accordance with the measured position, e.g. to maintain it stationary in spite of vibrations that might otherwise disturb it. The absolute sensor may be a capacitive or inductive sensor and the relative sensor may be an interferometer.

Abstract: In a lithographic projection apparatus, a reflective-type mask is attached to a compliant membrane on a mask table. The backside of the membrane is in turn attached to a plurality of actuators which are operable to deform the membrane. A mask level sensor can be used to detect the level of the mask and the actuators operate to keep the mask at a constant level. Additionally, the actuators may also serve to keep the mask flat and in the correct planar orientation.

Abstract: In a lithographic projection apparatus the positions and/or orientations of reflective optical elements is dynamically controlled. The position of a reflective optical element such as a mirror in an illumination or projection system is first measured using an absolute position sensor mounted on a reference frame and thereafter measured by a relative position sensor also mounted on said reference frame. The position of the element is controlled in accordance with the measured position, e.g. to maintain it stationary in spite of vibrations that might otherwise disturb it. The absolute sensor may be a capacitive or inductive sensor and the relative sensor may be an interferometer.

Abstract: In a lithographic projection apparatus, a reflective-type mask MA is attached to a compliant membrane 110 on a mask table MT. The backside of the membrane is in turn attached to a plurality of actuators 140 which are operable to deform the membrane. A mask level sensor can be used to detect the level of the mask and the actuators operate to keep the mask at a constant level. Additionally, the actuators may also serve to keep the mask flat and in the correct planar orientation. FIG.