Patent ID: 8134257

Claim:
A lithographic 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 to hold a substrate; a projection system configured to project the patterned radiation beam onto a target portion of the substrate; and an actuator constructed and arranged to produce a displacement force between a first and a second part to displace the first and second parts relative to each other, the actuator comprising: a first magnet subassembly, attached to one of the first and second parts, and configured to provide a magnetic field substantially perpendicular to the direction of the displacement force; and an electrically conductive element, attached to the other one of the first and second parts and placed near the first magnet subassembly, and configured to produce the displacement force by interaction of an electric current carried by the electrically conductive element and the magnetic field, the first magnet subassembly comprising at least one set of at least two adjacently placed magnets oriented such that their magnetic polarizations are substantially mutually opposite, and a back mass made of a magnetic flux guiding material and connecting the magnets to guide a magnetic flux there between, wherein the first magnet subassembly comprises a carrier made a non-magnetic-flux-guiding material, the carrier comprising at least one recess in which the at least one set of back mass and magnets is embedded, wherein the carrier is configured to carry at least three sets of a back mass and magnets, each set being placed along a respective bisector of an isosceles triangle, and wherein the carrier is made of a fiber reinforced plastic material and wherein fibers of the fiber reinforced plastic material in each set are arranged substantially along or substantially perpendicular to the respective bisector of the isosceles triangle.