Method for positioning a target portion of a substrate with respect to a focal plane of a projection system

Abstract

A method is provided for positioning a target portion of a substrate with respect to a focal plane of a projection system. The substrate may include one or more target portions. The method includes performing height measurements of at least part of the substrate to generate height data. The at least part of the substrate is at least partially outside the target portion that is to be positioned with respect to the projection system. The method further includes using predetermined correction heights to compute corrected height data for the height data corresponding to the at least part of the substrate outside the target portion, and positioning the target portion of the substrate with respect to the focal plane of the projection system at least partially based on the corrected height data.

1 . A method for positioning at least one target portion of a substrate with respect to a focal plane of a projection system, the method comprising:
 performing height measurements of at least part of the substrate to generate height data, wherein the at least part of the substrate is at least partially outside the target portion that is to be positioned with respect to the projection system;   using predetermined correction heights to compute corrected height data for the height data corresponding to at least one area of the at least part of the substrate that is located outside of the target portion; and   positioning the target portion of the substrate with respect to the focal plane of the projection system at least partially based on the corrected height data.   
   
   
       2 . A method according to  claim 1 , wherein the height measurements are performed by scanning the at least part of the substrate in a scanning direction with a level sensor. 
   
   
       3 . A method according to  claim 2 , wherein the level sensor is an optical sensor, a pneumatic sensor, a capacitive sensor, an air gauge, or a scanning needle profiler. 
   
   
       4 . 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   a level sensor configured to perform height measurements of at least part of the substrate to generate height data, for use in positioning a target portion of the substrate with respect to a focal plane of the projection system,   wherein the level sensor is arranged to generate additional height data with respect to at least part of the substrate that is at least partially outside the target portion that is to be positioned with respect to the projection system, and wherein the additional height data is corrected using predetermined correction heights.   
   
   
       5 . A method for generating correction heights to correct height data obtained by a level sensor measuring a substrate, the method comprising:
 performing height measurements of at least one target portion of the substrate to generate a height profile;   performing height measurements in an area outside the at least one target portion of the substrate to generate an additional height profile;   computing a level profile based on the height profile;   extrapolating the level profile to the area outside the at least one target portion that corresponds to the additional height profile, to provide an extrapolated level profile; and   determining correction heights by computing the difference between the extrapolated level profile and the additional height profile.   
   
   
       6 . A method according to  claim 5 , wherein the height profile is obtained by averaging height data obtained with respect to at least two target portions. 
   
   
       7 . A method according to  claim 5 , wherein the additional height profile is obtained by averaging height data obtained with respect to at least two target portions. 
   
   
       8 . A method according to  claim 5 , wherein the level profile is obtained by computing a fit through the height profile. 
   
   
       9 . 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   a level sensor configured to perform height measurements of at least part of the substrate to generate height data, for use in positioning a target portion of the substrate with respect to a focal plane of the projection system,   wherein the lithographic apparatus is arranged to:
 perform height measurements of at least one target portion of the substrate to generate a height profile, 
 perform height measurements in an area outside the at least one target portion of the substrate to generate an additional height profile, 
 compute a level profile based on the height profile, 
 extrapolate the level profile to the area outside the at least one target portion that corresponds to the additional height profile, to provide an extrapolated level profile, and 
 determine correction heights by computing the difference between the extrapolated level profile and the additional height profile. 
   
   
   
       10 . 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   a level sensor configured to perform height measurements of at least part of the substrate to generate height data, for use in positioning a target portion of the substrate with respect to a focal plane of the projection system,   wherein the lithographic apparatus further comprises a processor and a memory, the memory being encoded with a computer program containing instructions that are executable by the processor to perform a method for positioning the target portion of the substrate with respect to the focal plane of the projection system, wherein the method comprises:
 performing height measurements of at least part of the substrate to generate height data, wherein the at least part of the substrate is at least partially outside the target portion that is to be positioned with respect to the projection system; 
 using predetermined correction heights to compute corrected height data for the height data corresponding to at least one area of the at least part of the substrate that is located outside of the target portion; and 
 positioning the target portion of the substrate with respect to the focal plane of the projection system at least partially based on the corrected height data. 
   
   
   
       11 . 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   a level sensor configured to perform height measurements of at least part of the substrate to generate height data, for use in positioning a target portion of the substrate with respect to a focal plane of the projection system,   wherein the lithographic apparatus further comprises a processor and a memory, the memory being encoded with a computer program containing instructions that are executable by the processor to perform a method for calculating correction heights to correct height data obtained by the level sensor, wherein the method comprises:
 performing height measurements of the target portion of the substrate to generate a height profile; 
 performing height measurements in an area outside the target portion of the substrate to generate an additional height profile; 
 computing a level profile based on the height profile; 
 extrapolating the level profile to the area outside the target portion that corresponds to the additional height profile, to provide an extrapolated level profile; and 
 determining correction heights by computing the difference between the extrapolated level profile and the additional height profile. 
   
   
   
       12 . A system for controlling the position of a substrate, the system comprising a processor and a memory, the memory being encoded with a computer program containing instructions that are executable by the processor to perform, using height data, a method for positioning a target portion of the substrate with respect to a focal plane of a projection system, wherein the method comprises:
 performing height measurements of at least part of the substrate to generate the height data, wherein the at least part of the substrate is at least partially outside the target portion that is to be positioned with respect to the projection system;   using predetermined correction heights to compute corrected height data for the height data corresponding to at least one area of the at least part of the substrate that is located outside of the target portion; and   positioning the target portion of the substrate with respect to the focal plane of the projection system at least partially based on the corrected height data.   
   
   
       13 . A system according to  claim 12 , wherein the processor is adapted to communicate at least indirectly with an alignment sensor and is adapted to control at least indirectly the position the substrate. 
   
   
       14 . A system for controlling the position of a substrate, the system comprising a processor and a memory, the memory being encoded with a computer program containing instructions that are executable by the processor to perform a method for calculating correction heights to correct height data obtained by a level sensor, wherein the method comprises:
 performing height measurements of a target portion of the substrate to generate a height profile;   performing height measurements in an area outside the target portion of the substrate to generate an additional height profile;   computing a level profile based on the height profile;   extrapolating the level profile to the area outside the target portion that corresponds to the additional height profile, to provide an extrapolated level profile; and   determining correction heights by computing the difference between the extrapolated level profile and the additional height profile.   
   
   
       15 . A system according to  claim 14 , wherein the processor is adapted to communicate at least indirectly with an alignment sensor and is adapted to control at least indirectly the position the substrate. 
   
   
       16 . A computer-readable medium encoded with a computer program containing instructions that are executable by the processor to perform, using height data, a method for positioning a target portion of a substrate with respect to a focal plane of a projection system, wherein the method comprises:
 performing height measurements of at least part of the substrate to generate the height data, wherein the at least part of the substrate is at least partially outside the target portion that is to be positioned with respect to the projection system;   using predetermined correction heights to compute corrected height data for the height data corresponding to at least one area of the at least part of the substrate that is located outside of the target portion; and   positioning the target portion of the substrate with respect to the focal plane of the projection system at least partially based on the corrected height data.   
   
   
       17 . A computer-readable medium encoded with a computer program containing instructions that are executable by the processor to perform a method for calculating correction heights to correct height data obtained by a level sensor, wherein the method comprises:
 performing height measurements of a target portion of the substrate to generate a height profile;   performing height measurements in an area outside the target portion of the substrate to generate an additional height profile;   computing a level profile based on the height profile;   extrapolating the level profile to the area outside the target portion that corresponds to the additional height profile, to provide an extrapolated level profile; and   determining correction heights by computing the difference between the extrapolated level profile and the additional height profile.