Integrated plane mirror and differential plane mirror interferometer system

An interferometer system for measuring displacement along at least two directions in an XYZ system of co-ordinates, of an object in a plane substantially parallel to an XY plane, said interferometer system comprising:

• at least one measuring mirror fixedly connected to said object and comprising a plurality of measuring mirror areas;
• at least one reference mirror comprising one or more reference mirror areas;
• a beam generator configured to generate a plurality of radiation beams, said beam generator comprising a beam-splitter block having a beam-splitting surface;
• a plurality of radiation-sensitive detectors configured to convert radiation beams reflected towards said detectors into electric measuring signals;
• wherein said beam-splitting surface of the beam-splitter block is configured to split at least one first beam of said plurality of radiation beams into a first measuring beam and a first reference beam, said first reference beam only being reflected by one or more first reference mirrors located in a fixed position with respect to said beam-splitter block, said first measuring beam being reflected by a first measuring mirror area of said plurality of measuring mirror areas, and
• wherein said beam-splitting surface of the beam-splitter block is configured to split at least one second beam of said plurality of radiation beams into a second measuring beam and a second reference beam, said second measuring beam being reflected by a second measuring mirror area of said plurality of measuring mirror areas, and said second reference beam being reflected by a first reflector that is fixedly positioned with respect to said beam-splitter block and by at least one third mirror area, which is movable with respect to said beam-splitter block, and
• wherein, in use, the second reference beam associated with the at least one second beam exits the first reflector in a direction substantially orthogonal to the direction of the first reference beam associated with the at least one first beam exits the beam-splitter block and away from the beam-splitter block.

A lithographic apparatus comprising:

• an illumination system configured to provide a beam of radiation;
• a pattern support configured to support a patterning device that serves to impart said beam of radiation with a pattern in its cross-section;
• a substrate support configured to hold a substrate;
• a projection system configured to project said patterned beam onto a target portion of the substrate;
• and
• an interferometer system configured to measure displacement of one of the supports, wherein said interferometer system comprises,
• a plane mirror interferometer system;
• a differential plane mirror interferometer system;
• a beam-splitter configured to split a beam associated with said plane mirror interferometer system and a beam associated with said differential plane mirror interferometer system into respective measuring beams and respective reference beams;
• at least one measuring mirror fixedly connected to said one of the supports and comprising a plurality of measuring mirror areas;
• at least one reference mirror comprising one or more reference mirror areas, and
• wherein, in use, a direction of propagation of the reference beam associated with the differential plane mirror interferometer system just before incidence on a reference mirror is in a direction substantially orthogonal to the direction of the reference beam associated with the plane mirror interferometer just before incidence on a reference mirror and away from the beam-splitter.

A lithographic apparatus comprising:

• an illumination system configured to provide a beam of radiation;
• a pattern support configured to support a patterning device that serves to impart said beam of radiation with a pattern in its cross-section;
• a substrate support configured to hold a substrate;
• a projection system configured to project said patterned beam onto a target portion of the substrate;
• and
• an interferometer system configured to measure displacement of one of the supports, wherein said interferometer system comprises,
• at least one measuring mirror fixedly connected to the one of the supports, said at least one measuring mirror comprising a plurality of measuring mirror areas;
• at least one reference mirror comprising one or more reference mirror areas that are configured to prevent beams from passing through said reference mirror;
• a beam generator configured to generate a plurality of beams, said beam generator comprising a beam-splitter block having a beam-splitting surface;
• and
• a plurality of radiation-sensitive detectors configured to convert radiation beams reflected towards said detectors into electric measuring signals,
• wherein said beam-splitting surface of the beam-splitter block is configured to split at least one first beam of said plurality of radiation beams into a first measuring beam and a first reference beam, said first reference beam only being reflected by one or more first reference mirrors located in a fixed position with respect to said beam-splitter block, said first measuring beam being reflected by a first measuring mirror area of said plurality of measuring mirror areas,
• wherein said beam-splitting surface of the beam-splitter block is configured to split at least one second beam of said plurality of radiation beams into a second measuring beam and a second reference beam, said second measuring beam being reflected by a second measuring mirror area of said plurality of measuring mirror areas, and said second reference beam being reflected by a first reflector that is fixedly positioned with respect to said beam-splitter block and by at least one third mirror area, which is movable with respect to said beam-splitter block, and
• wherein, in use, the second reference beam associated with the at least one second beam exits the first reflector in direction substantially orthogonal to the direction the first reference beam associated with the at least one first beam exits the beam-splitter block and away from the beam-splitter block.

A device manufacturing method comprising:

• providing a beam of radiation using an illumination system;
• using a patterning device to impart the beam of radiation with a pattern in its cross-section, the patterning device supported by a pattern support;
• projecting said patterned beam of radiation onto a target portion of a substrate, the substrate held by a substrate support;
• and
• determining a position of one of the supports with an interferometer system, the determining including:
• splitting at least a first beam of a plurality of beams, using a beam-splitting surface of a beam-splitter block, into a first measuring beam and a first reference beam, said first reference beam only being reflected by one or more first reference mirrors located in a fixed position with respect to said beam-splitter block, said first measuring beam being reflected by a first measuring mirror area of a plurality of measuring mirror areas, the plurality of measuring mirror areas part of at least one measuring mirror fixedly connected to the one of the supports, and
• splitting at least a second beam of said plurality of beams, using the beam-splitting surface of said beam-splitter block, into a second measuring beam and a second reference beam, said second measuring beam being reflected by a second measuring mirror area of said plurality of measuring mirror areas, and said second reference beam being reflected by a first reflector that is fixedly positioned with respect to said beam-splitter block and by at least one third mirror area, which is movable with respect to said beam-splitter block, and said second reference beam being reflected in a substantially orthogonal direction with respect to the first reference beam by the first reflector and away from the beam-splitter block, and
• converting beams which are reflected towards detectors into electric measuring signals.