Lithographic apparatus and method for determining Z position errors/variations and substrate table flatness

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.

1 . A measurement system for measuring the displacement of a moveable object relative to a base along at least a first direction of measurement, said movable object having at least one reference part that is moveable in a plane of movement relative to said base in which the actual movement of said reference part is limited to within an area bounded by a closed contour, said measurement system comprising: 
 a planar element having a shape that is substantially similar to the closed contour shape of said bounded area;    a sensor head configured to operatively cooperate with said planar element to determine displacement of said movable object,    wherein said planar element and said sensor head are arranged so that said sensor head is mounted to said reference part of said moveable object or said planar element is mounted to said base and said sensor head is mounted to said reference part of said moveable object.    
   
   
       2 . A lithographic apparatus, comprising: 
 an illumination system for providing a beam of radiation;    a support structure for supporting a patterning device that imparts said beam radiation with a pattern in its cross-section;    a substrate holder for holding a substrate having a target portion;    a projection system for projecting said patterned beam onto said target portion of said substrate;    a moveable object having at least one reference part that is moveable in a plane of movement relative to a base in which the actual movement of said reference part is limited to within an area bounded by a closed contour; and    a measurement system for measuring displacement of said moveable object relative to a base along at least a first direction of measurement, said measurement system comprising: 
 a planar element having a shape that is substantially similar to the closed contour shape of said bounded area;  
 a sensor head configured to operatively cooperate with said planar element to determine displacement of said movable object, and  
 wherein said planar element and said sensor head are arranged so that said sensor head is mounted to said reference part of said moveable object or said planar element is mounted to said base and said sensor head is mounted to said reference part of said moveable object.  
   
   
   
       3 . The lithographic apparatus of  claim 2 , wherein the first direction of measurement lies within a plane that is at least substantially parallel to the plane of movement.  
   
   
       4 . The lithographic apparatus of  claim 2 , wherein the first direction of measurement is at least substantially perpendicular to the plane of movement.  
   
   
       5 . The lithographic apparatus of  claim 3 , wherein said sensor head is an encoder head and said planar element is a ruler comprising a grating.  
   
   
       6 . The lithographic apparatus of  claim 4 , wherein said sensor head is an interferometer and said planar element is a mirror.  
   
   
       7 . The lithographic apparatus of  claim 4 , wherein said sensor head is capacitive sensor and said planar element is an electrically conductive element.  
   
   
       8 . The lithographic apparatus of  claim 2 , wherein said closed contour is a circle.  
   
   
       9 . The lithographic apparatus of  claim 2 , further including: 
 said moveable object comprising at least two reference parts that are located at known relative positions, and    said measurement system is configured to measure displacement of at least two reference parts relative to said base in a first direction and to measure displacement of at least one reference part relative to said base in a second direction, with said first and second directions being different,    wherein, based on said measurements, translational displacements of said reference parts relative to said base in the first direction and second direction as well as rotational displacement of the reference parts relative to said base around an axis perpendicular to the plane defined by the first and the second direction of measurement, can be determined.    
   
   
       10 . The lithographic apparatus of  claim 2 , wherein said movable object is a reticle stage.  
   
   
       11 . The lithographic apparatus of  claim 2 , wherein said movable object is said substrate holder.  
   
   
       12 . The lithographic apparatus of  claim 11 , wherein said closed contour has substantially the same shape as the substrate shape.  
   
   
       13 . A measurement system for measuring displacement of a moveable object relative to a base along six degrees of freedom, said measurement system comprising: 
 at least three primary measurement units for measuring translational displacement of the moveable object relative to the base in a first direction;    at least two secondary measurement units for measuring translational displacement of said moveable object relative to said base in a second direction differing from the first direction,    at least one tertiary measurement unit for measuring translational displacement of the moveable object relative to the base in a third direction differing from the first direction and from the second direction and extending at an angle relative to a directional plane that is defined by a combination of the first direction and the second direction,    wherein said measurement units are located at known relative positions,    wherein each of said measurement unit comprises a sensor head and a planar element in which said sensor head is configured to transmit a beam to said planar element and said planar element is configured to reflect said beam to said sensor head in order to measure translational displacement of said sensor head relative to said planar element,    wherein said measurement units are combined into at least three measurement assemblies, each of said three measurement assemblies comprising a primary measurement unit and at least one of a secondary measurement unit and a tertiary measurement unit, and    wherein the directions associated with said measurement units of a single measurement assembly together define a measurement plane, each of the planar elements of a single measurement assembly being arranged parallel to said measurement plane.    
   
   
       14 . A lithographic apparatus, comprising: 
 an illumination system for providing a beam of radiation;    a support structure for supporting a patterning device that imparts said beam radiation with a pattern in its cross-section;    a substrate holder for holding a substrate having a target portion;    a projection system for projecting said patterned beam onto said target portion of said substrate;    a moveable object that is moveable relative to a base; and    a measurement system for measuring displacement of said moveable object relative to said base along six degrees of freedom, said measurement system comprising: 
 at least three primary measurement units for measuring translational displacement of the moveable object relative to the base in a first direction;  
 at least two secondary measurement units for measuring translational displacement of said moveable object relative to said base in a second direction differing from the first direction,  
 at least one tertiary measurement unit for measuring translational displacement of the moveable object relative to the base in a third direction differing from the first direction and from the second direction and extending at an angle relative to a directional plane that is defined by a combination of the first direction and the second direction,  
 wherein said measurement units are located at known relative positions,  
 wherein each of said measurement unit comprises a sensor head and a planar element in which said sensor head is configured to transmit a beam to said planar element and said planar element is configured to reflect said beam to said sensor head in order to measure translational displacement of said sensor head relative to said planar element,  
 wherein said measurement units are combined into at least three measurement assemblies, each of said three measurement assemblies comprising a primary measurement unit and at least one of a secondary measurement unit and a tertiary measurement unit, and  
 wherein the directions associated with said measurement units of a single measurement assembly together define a measurement plane, each of the planar elements of a single measurement assembly being arranged parallel to said measurement plane.  
   
   
   
       15 . The lithographic apparatus of  claim 14 , wherein the first direction is substantially perpendicular to the second direction and the third direction is substantially perpendicular to the plane defined by the first direction and the second direction.  
   
   
       16 . The lithographic apparatus of  claim 14 , wherein at least one measurement unit is an encoder unit, the associated sensor head being an encoder head and the associated planar element being a grating.  
   
   
       17 . The lithographic apparatus of  claim 16 , wherein the planar elements of a measurement assembly are combined into a two-dimensional grating.  
   
   
       18 . The lithographic apparatus of  claim 17 , wherein the two-dimensional grating is provided in a checkerboard pattern.  
   
   
       19 . The lithographic apparatus of  claim 15 , wherein the measurement system comprises means for determining at least one of the average pitch between a plurality of lines and transitions of the grating.  
   
   
       20 . The lithographic apparatus of  claim 15 , wherein the measurement system comprises at least one of a map of said plurality of lines and areas of the grating.  
   
   
       21 . The lithographic apparatus of  claim 14 , wherein the displacement of the moveable object in a first translational degree of freedom is significantly larger than displacements of the moveable object in the other translational degrees of freedom, and wherein the direction of measurement associated with the primary measurement units is substantially equal to the direction of the first translational degree of freedom.  
   
   
       22 . The lithographic apparatus of  claim 14 , wherein the moveable object has at least one reference part that is moveable in a plane of movement relative to said base in which the actual movement of said reference part is limited to within an area bounded by a closed contour, and 
 wherein at least one planar element of at least one measurement assembly has a measurement plane that is substantially parallel to the plane of movement has a shape that is essentially identical to the shape of the contour.    
   
   
       23 . The lithographic apparatus of  claim 14 , wherein the moveable object is a short stroke unit of a reticle stage and the base is a long stroke unit of said reticle stage.  
   
   
       24 . The lithographic apparatus of  claim 14 , wherein at least one sensor head is mounted onto the base, and the planar element associated with said sensor head is mounted onto the moveable object.  
   
   
       25 . The lithographic apparatus of  claim 14 , wherein at least one planar element is mounted onto the base, and the sensor head associated with said planar element is mounted onto the moveable object.  
   
   
       26 . The lithographic apparatus of  claim 14 , wherein the movable object is a reticle stage.  
   
   
       27 . The lithographic apparatus of  claim 14 , wherein the movable object is a substrate holder for holding a substrate.  
   
   
       28 . A lithographic apparatus, comprising: 
 an illumination system for providing a beam of radiation;    a support structure for supporting a patterning device that imparts said beam radiation with a pattern in its cross-section;    a substrate holder for holding a substrate having a target portion;    a projection system for projecting said patterned beam onto said target portion of said substrate;    a moveable object that is moveable relative to a base, said moveable object comprising a grating that is integrated with said movable object; and    a measurement system comprising an encoder head for measuring displacement of the moveable object relative to the base along a first translational direction of measurement in cooperation with the grating of the moveable object,    
   
   
       29 . The lithographic apparatus of  claim 28 , wherein the movable object comprises printed grating lines or printed grating areas.  
   
   
       30 . The lithographic apparatus of  claim 28 , wherein the moveable object comprises grating lines or grating areas that are applied to the moveable object by means of vapor deposition.  
   
   
       31 . The lithographic apparatus of  claim 28 , wherein the moveable object comprises grating lines or grating areas that are etched into the moveable object.  
   
   
       32 . A device manufacturing method comprising: 
 providing a substrate having a target portion;    providing a beam of radiation;    imparting said beam of radiation with a desired pattern in its cross-section;    projecting the patterned beam of radiation onto the target portion of the substrate,    measuring the displacement of a moveable object relative to a base along at least a first direction of measurement, said movable object having at least one reference part that is moveable in a plane of movement relative to said base in which the actual movement of said reference part is limited to within an area bounded by a closed contour;    measuring displacement of the moveable object relative to a base along at least a first direction of measurement by employing a measurement system,    wherein said measurement system comprises a sensor head and a planar element associated with said sensor head, the sensor head being mounted onto the base and the planar element being mounted onto the reference part of the moveable object or the planar element being mounted onto the base and the sensor head being mounted onto the reference part of the moveable object;    wherein the planar element has a shape that is substantially similar to the shape of the closed contour.    
   
   
       33 . A device manufacturing method comprising: 
 providing a substrate having a target portion;    providing a beam of radiation;    imparting said beam of radiation with a desired pattern in its cross-section;    projecting the patterned beam of radiation onto the target portion of the substrate,    measuring displacement of the moveable object relative to the base along six degrees of freedom by employing a measurement system,    wherein said measurement system comprises at least three primary measurement units for measuring translational displacement of the moveable object relative to the base in a first direction, at least two secondary measurement units for measuring translational displacement of the moveable object relative to the base in a second direction differing from the first direction, at least one tertiary measurement unit for measuring translational displacement of the moveable object relative to the base in a third direction differing from the first direction and from the second direction and extending at an angle relative to a directional plane, which directional plane is defined by a combination of the first direction and the second direction,    wherein said measurement units are located at known relative positions,    wherein each of said measurement unit comprises a sensor head and a planar element in which said sensor head is configured to transmit a beam to said planar element and said planar element is configured to reflect said beam to said sensor head in order to measure translational displacement of said sensor head relative to said planar element,    wherein said measurement units are combined into at least three measurement assemblies, each of said three measurement assemblies comprising a primary measurement unit and at least one of a secondary measurement unit and a tertiary measurement unit, and    wherein the directions associated with said measurement units of a single measurement assembly together define a measurement plane, each of the planar elements of a single measurement assembly being arranged parallel to said measurement plane.    
   
   
       34 . A device manufacturing method, comprising: 
 providing a substrate having a target portion;    providing a beam of radiation;    imparting said beam of radiation with a desired pattern in its cross-section;    projecting the patterned beam of radiation onto the target portion of the substrate,    providing a moveable object, which is moveable relative to a base, the moveable object comprising an integrated grating; and    measuring displacement of the moveable object relative to the base in a first translational direction of measurement in cooperation with the grating of the moveable object by employing a measurement system,    wherein said measurement system comprises an encoder head.