Patent ID: 8582082

Claim:
A lithographic projection apparatus comprising: a support constructed to support a patterning device, the patterning device being capable of imparting a radiation beam with a pattern in its cross-section to form a patterned radiation beam; a substrate table constructed and arranged to hold a substrate; a projection system constructed and arranged to project the patterned radiation beam onto a target portion of the substrate; a level sensor constructed and arranged to perform height measurements of at least part of the substrate to generate height data, for use in positioning a target portion of the substrate with respect to a focal plane of the projection system, wherein the level sensor comprises: a projection part configured to direct radiation onto the substrate, the projection part comprising a radiation source and a projection grid having slits positioned downstream from the radiation source, and a detection part configured to detect reflected radiation from the substrate surface, the detection part comprising a detector and a detection grid having slits positioned in between the substrate and the detector; a first actuator constructed and arranged to move the substrate table at least in a first direction perpendicular to an edge of the substrate having a maximum speed; a second actuator constructed and arranged to move the substrate table at least in a second direction perpendicular to a surface of the substrate having a maximum speed; and a controller constructed and arranged to generate a stroke of relative movement between the substrate and the level sensor, by controlling the first and second actuator, wherein the controller is constructed and arranged to combine first and second actuator movement to effect combined movement at a speed higher than the maximum speed of one actuator, and wherein the level sensor is configured to project and detect level sensor spots that are rotated to align with the stroke of relative movement between the substrate and the level sensor so as to change a width of the level sensor spots to be greater than a width that the level sensor spots would be if the level sensor spots are not aligned with the stroke of relative movement, and wherein the combined movement of the actuators and the increase in the width of the level sensor spots decrease a time to perform the height measurements.