Abstract: A device manufacturing method includes projecting a patterned beam of radiation onto a substrate, wherein the position of a movable object is determined in a number of degrees of freedom using a number of sensors, the number of sensors being larger than the number of degrees of freedom, wherein the position of the movable object in the number of degrees of freedom is determined using signals of each of the sensors, wherein the signals of the sensors are weighed on the basis of the difference between noise levels of each of the sensors. Accuracy of the position measurement of movable object and/or overlay and focus performance are improved in lithographic apparatus.

Abstract: The invention pertains to a measurement system for measuring displacement of a moveable object relative to a base in at least a first direction of measurement, the moveable object having at least one reference part that is moveable in a plane of movement relative to the base, the actual movements of the reference part being within an area of said plane of movement that is bounded by a closed contour having a shape. The measurement system comprises a sensor head that operatively communicates with a planar element. The sensor head is mounted onto the base and the planar element being mounted onto the reference part of the moveable object or the other way around, wherein the planar element has a shape that is essentially identical to the shape of the closed contour.

Abstract: In an interferometric displacement measuring system, a correction for beamshear is made. The correction may be a polynomial of a variable proportional to the length of the optical path traversed by the measurement beam and the angle of the measurement mirror. The correction compensates for errors caused by non-planarity of the wavefront of the measurement beam.