Lithography system with differential interferometer module

Abstract

The invention relates to a lithography system comprising an optical column, a moveable target carrier for displacing a target such as a wafer, and a differential interferometer module, wherein the interferometer module is adapted for emitting three reference beams towards a first mirror and three measurement beams towards a second mirror for determining a displacement between said first and second mirror. In a preferred embodiment the same module is adapted for measuring a relative rotation around two perpendicular axes as well. The present invention further relates to an interferometer module and method for measuring such a displacement and rotations.

1 . Differential interferometer module comprising:
 a housing or structure comprising:   three measurement beam openings for emitting three measurement beams and for receiving reflections thereof back into the module; and   three reference beam openings for emitting three reference beams and for receiving reflections thereof back into the module;   a kinematic mount for alignment of the module with respect to a frame;   wherein said three measurement beam openings are arranged non-collinearly and said three reference beam openings are arranged non-collinearly.   
     
     
         2 . Module according to  claim 1 , wherein said three measurement beam openings are arranged in an L-configuration, and wherein said three reference beam openings are arranged in an L-configuration. 
     
     
         3 . Module according to  claim 2 , wherein the L-configuration formed by the three measurement beam openings and the L-configuration formed by the three reference beam openings are positioned in substantially the same orientations. 
     
     
         4 . Module according to  claim 1 , wherein the three measurement beam openings comprise a first, a second and a third measurement beam opening and the three reference beam openings comprise a first, a second, and a third reference beam opening,
 wherein the first measurement beam opening and the second measurement beam opening are arranged along a first line and the first reference beam opening and the second reference beam opening are arranged along a second line, wherein the first line and the second line are parallel, and/or   wherein the second measurement beam opening, the third measurement beam opening, the second reference beam opening and the third reference beam opening are arranged along one line.   
     
     
         5 . Module according to  claim 1 , wherein a first measurement beam and second measurement beam span a third plane, and the second measurement beam and a third measurement beam span a fourth plane, wherein the third plane is at an angle α of substantially 90 degrees with respect to the fourth plane, and
 wherein a first reference beam and a second reference beam span a first plane, and the second reference beam and a third reference beam span a second plane, wherein the second plane is at substantially the same angle α with respect to the first plane. 
 
     
     
         6 . Module according to  claim 1 , wherein the three measurement beams are substantially parallel to each other and/or the three reference beams are substantially parallel to each other. 
     
     
         7 . Module according to  claim 1 , wherein each of said three measurement beams is substantially parallel to its associated incident reference beam. 
     
     
         8 . Module according to  claim 1 , wherein said kinematic mount has a fixed spatial relationship with the measurement beam openings and with the reference beam openings. 
     
     
         9 . Module according to  claim 1 , wherein said kinematic mount has a specified spatial relationship with the measurement beams and the reference beams. 
     
     
         10 . Module according to  claim 1 , further comprising a beam source comprising an optical fiber, the optical fiber being connected to a laser emitter arranged outside of the module. 
     
     
         11 . Module according to  claim 1 , arranged for providing one or more electrical signals representing a combined beam, the combined beam formed by a reflected measurement beam combined with a reflected reference beam, the module comprising beam intensity detectors adapted for converting an intensity of a combined beam to an electrical signal, wherein said electrical signal is not amplified within the module. 
     
     
         12 . Module according to  claim 1 , comprising beam receivers for receiving combined beams formed by a reflected measurement beam combined with a reflected reference beam, wherein the beam receivers comprise fiber ends of optical fibers leading out of the module, whereby one or more signals provided by the interferometer module comprises an optical signal received by a beam receiver. 
     
     
         13 . System comprising:
 a vacuum chamber;   a frame arranged within the vacuum chamber;   a differential interferometer module according to  claim 1  mounted on said frame via said kinematic mounts.   
     
     
         14 . System according to  claim 13 , further comprising a beam source comprising a laser emitter arranged outside the vacuum chamber and connected to an optical fiber extending from said laser emitter through a wall of the vacuum chamber and into the differential interferometer module. 
     
     
         15 . System according to  claim 13 , comprising a second differential interferometer module according to  claim 1  mounted on said frame via its kinematic mounts, said second differential interferometer module arranged such that its measurement beams and reference beams are directed in a direction substantially perpendicular to the measurement beams and reference beams of said differential interferometer module. 
     
     
         16 . System according to  claim 15 , further comprising a beam source comprising a laser emitter arranged outside the vacuum chamber,
 wherein the first differential interferometer module is connected to the beam source via an optical fiber extending from said laser emitter through a wall of the vacuum chamber and into the differential interferometer module, and   wherein the second differential interferometer module is connected to the beam source via a second optical fiber.   
     
     
         17 . A lithography system comprising:
 a frame to which an optical column having an optical axis is mounted, the optical column adapted for projecting a plurality of exposure beamlets onto a target;   a carrier for holding the target and for moving the target relative to the optical column;   a differential interferometer module, mounted to the frame by means of a kinematic mount;   a beam source for supplying a beam of coherent light to said differential interferometer module;   wherein the carrier comprises a first mirror, comprising a substantially planar surface at substantially the same level or height within the system as the target or exposure surface thereof, and   wherein the optical column comprises a second mirror, which comprises a substantially planar surface close to the projection end of the optical column,   wherein the differential interferometer module is arranged to emit measurement beams onto the first mirror and reference beams onto the second mirror and for receiving reflections of the measurement beams and of the reference beams for measuring a relative movement between the first mirror and the second mirror.   
     
     
         18 . Lithography system according to  claim 17 , wherein said beam source comprises a laser unit which is coupled into the interferometer module via an optical fiber. 
     
     
         19 . Lithography system according to  claim 17 , further comprising:
 an additional first mirror comprising a substantially planar surface at substantially the same level or height within the system as the target or exposure surface thereof, the additional first mirror arranged in a plane substantially perpendicular to the first mirror;   an additional a second mirror, which comprises a substantially planar surface close to the projection end of the optical column, the additional second mirror arranged in a plane substantially perpendicular to the second mirror;   a second differential interferometer module, arranged to emit measurement beams onto the additional first mirror and reference beams onto the additional second mirror,   wherein the second differential interferometer module is arranged such that the measurement beams and reference beams emitted by the second differential interferometer module are directed in a direction substantially perpendicular to the measurement beams and reference beams of said differential interferometer module.   
     
     
         20 . Lithography system according to  claim 17 , wherein the measurement beams comprise three measurement beams, and the reference beams comprise three reference beams, and a relative movement between the first mirror and second mirror is measured by evaluating interference between a measurement beam and its associated reference beam. 
     
     
         21 . Lithography system according to  claim 17 , further comprising a vacuum housing, the differential interferometer, the frame and the carrier being arranged within the vacuum housing;
 wherein the beam source comprises a laser unit arranged outside the vacuum chamber and an optical fiber from the laser unit passing through a wall of said vacuum chamber through a vacuum feed-through.   
     
     
         22 . Lithography system according to  claim 17 , wherein signals representative of interference between measurement beams and associated reference beams are transported from the differential interferometer module out of the vacuum chamber via signal wires which pass through a second vacuum feed-through. 
     
     
         23 . Lithography system according to  claim 17 , further comprises a signal processing module and a stage control unit for controlling movement of the carrier, the signal processing module adapted for providing a position and/or displacement signal to the stage control unit.