Interferometer system, method of determining a mode hop of a laser source of an interferometer system, method of determining a position of a movable object, and lithographic apparatus

Abstract

An interferometer system including: an optical system arranged to split a radiation beam from a laser source into a first beam along a first optical path and a second beam along a second optical path, and recombine the first beam and the second beam to a recombined beam, a detector to receive the recombined beam and to provide a detector signal based on the received recombined beam, and a processing unit, wherein a first optical path length of the first optical path and a second optical path length of the second optical path have an optical path length difference, and wherein the processing unit is arranged to determine a mode hop of the laser source on the basis of a phase shift in the detector signal.

1 - 15 . (canceled) 
     
     
         16 . An interferometer system to determine a displacement of an object of interest, the interferometer system comprising:
 an optical system arranged to split a radiation beam from a radiation source into a measurement beam along a first optical path and a reference beam along a second optical path, wherein the optical system is arranged to recombine the measurement beam and the reference beam to a recombined beam,   a detector to receive the recombined beam and to provide a detector signal on the basis of the received recombined beam,   a processing unit to process the detector signal,   an optical input fiber to guide the radiation beam from the radiation source to the optical system, and   an optical output fiber to guide the recombined beam from the optical system to the detector, wherein the optical input fiber and the optical output fiber are different fibers.   
     
     
         17 . The interferometer system of  claim 16 , further comprising a probe head,
 wherein the optical system is arranged in the probe head, and   wherein the optical input fiber and the optical output fiber are connected to the probe head.   
     
     
         18 . The interferometer system of  claim 16 , wherein the optical system is free of optical fibers. 
     
     
         19 . The interferometer system of  claim 16 , wherein the optical system comprises at least one reflective surface at a non-perpendicular angle with an optical path of the radiation beam, the measurement beam, the reference beam and/or the recombined beam reflected on the reflective surface. 
     
     
         20 . The interferometer system of  claim 19 , wherein the at least one reflective surface comprises a semi-transparent mirror arranged to split the radiation beam into the measurement beam and the reference beam. 
     
     
         21 . The interferometer system of  claim 19 , wherein the optical system comprises a first reflective surface arranged at a first non-perpendicular angle with the first optical path of the measurement beam and a second reflective surface arranged at a second non-perpendicular angle with the second optical path of the reference beam. 
     
     
         22 . The interferometer system of  claim 21 , wherein the first non-perpendicular angle and the second non-perpendicular angle are the same. 
     
     
         23 . The interferometer system of  claim 19 , wherein the at least one reflective surface is arranged to reflect the radiation beam, reference beam and/or the measurement beam. 
     
     
         24 . The interferometer system of  claim 19 , wherein the optical system comprises a gradient index lens having a lens body with a main radiation axis, wherein the lens body comprises a fiber side and a radiation side opposite to the fiber side, wherein the optical input fiber and the optical output fiber are arranged at the fiber side of the lens body, wherein at least the measurement beam is emitted and received at the radiation side, and wherein an outer surface of the lens body at the radiation side is arranged at a non-perpendicular angle with the main radiation axis to define the at least one reflective surface at the non-perpendicular angle. 
     
     
         25 . The interferometer system of  claim 19 , wherein the optical system comprises a focus lens to receive the radiation beam from an output end of the optical input fiber and to focus the recombined beam into an input end of the optical output fiber, wherein the output end and the input end are spaced at a distance of:
         d = f * tan       2   α       ,           wherein d is the distance between the output end and the input end, wherein f is a focal length of the focus lens, and wherein α is the angular difference between the non-perpendicular angle and a plane perpendicular with the optical path.   
     
     
         26 . The interferometer system of  claim 25 , wherein the distance between the output end of the optical input fiber and the input end of the optical fiber output fiber is selected to be equal to or larger than a minimum value to prevent that stray radiation of the radiation beam, measurement and/or reference beam is received by the input end of the optical output fiber. 
     
     
         27 . The interferometer system of  claim 16 , wherein the optical system comprises a circulator, having a first fiber port to which the optical input fiber is connected, a second fiber port to which the optical output fiber is connected, and a radiation port which is arranged to emit and receive radiation, wherein the circulator is arranged to guide the radiation beam received from the optical input fiber to the radiation port and to guide the recombined beam received at the radiation port to the optical output fiber. 
     
     
         28 . The interferometer system of  claim 27 , wherein the circulator is arranged in a probe head comprising the optical system. 
     
     
         29 . A lithographic apparatus comprising:
 a mask support constructed to support a patterning device having a pattern;   a substrate support constructed to support a substrate;   a projection system arranged to project the pattern onto the substrate, wherein the mask support, substrate support or projection system comprises an object of interest; and   the interferometer system as claimed in  claim 16  to determine the position of the object of interest.   
     
     
         30 . A lithographic apparatus comprising:
 a mask support constructed to support a patterning device having a pattern;   a substrate support constructed to support a substrate having a marker;   a projection system arranged to project the pattern onto the substrate;   a cooling hood to provide cooling; and   the interferometer system as claimed in  claim 16  to determine a position of the cooling hood.   
     
     
         31 . A method comprising:
 using an optical input fiber to guide a radiation beam from a radiation source to an optical system of an interferometer system, the interferometer system configured to determine a displacement of an object of interest;   splitting, using the optical system, the radiation beam into a measurement beam along a first optical path and a reference beam along a second optical path, wherein the optical system recombines the measurement beam and the reference beam to a recombined beam;   using an optical output fiber to guide the recombined beam from the optical system to a detector, wherein the optical input fiber and the optical output fiber are different fibers;   detecting, by the detector, the recombined beam to provide a detector signal on the basis of the received recombined beam; and   processing the detector signal.   
     
     
         32 . The method of  claim 31 , wherein the optical system comprises at least one reflective surface at a non-perpendicular angle with an optical path of the radiation beam, the measurement beam, the reference beam and/or the recombined beam reflected on the reflective surface. 
     
     
         33 . The method of  claim 31 , wherein the optical system comprises a circulator, having a first fiber port to which the optical input fiber is connected, a second fiber port to which the optical output fiber is connected, and a radiation port which is arranged to emit and receive radiation, and comprising guiding the radiation beam received from the optical input fiber to the radiation port and guiding the recombined beam received at the radiation port to the optical output fiber. 
     
     
         34 . The method of  claim 31 , wherein the optical system is free of optical fibers. 
     
     
         35 . The method of  claim 31 , further comprising:
 patterning a radiation beam using a patterning device supported by a mask support;   projecting, using a projection system, the patterned radiation beam onto a substrate supported by a substrate support, wherein the mask support, substrate support or projection system comprises an object of interest; and   processing the detector signal to determine the position of the object of interest.