Mask for clamping apparatus, e.g. for a lithographic apparatus

Abstract

An apparatus for supporting a mask comprises a pair of members. The mask held against each member by a vacuum arrangement which prevents relative motion between the mask and members. The members are compliant such that they accommodate flatness variations in the mask but without deforming the mask.

1. A lithographic projection apparatus for imaging of a mask pattern in a mask onto a substrate provided with a radiation-sensitive layer, the apparatus comprising:
 a radiation system constructed and arranged to supply a projection beam of radiation;  
 a first object table for holding a mask having a stiffness;  
 a second object table for holding a substrate;  
 a projection system constructed and arranged to image irradiated portions of the mask onto target portions of the substrate;  
 said mask table  first object table including at least one compliant member constructed and arranged to hold said mask such that, when the mask is held by said at least one compliant member, said at least one compliant member yields under the weight of the mask to conform substantially to a profile of the mask, and supports substantially the entire weight of the mask without a support, under a point of contact between the mask and the compliant member, to support substantially the entire weight of the mask, wherein a portion of said at least one compliant member is in direct contact with said mask and said portion has a stiffness lower than the stiffness of the mask.  
 
     
     
       2. An apparatus according to  claim 1 , wherein said at least one member comprises a pair of parallel strips. 
     
     
       3. An apparatus according to  claim 2 , wherein each strip is supported along its length. 
     
     
       4. An apparatus according to  claim 2 , wherein each strip is supported substantially at each end across its width. 
     
     
       5. An apparatus according to  claim 1 , further comprising a vacuum space constructed and arranged to hold said mask against said at least one member. 
     
     
       6. An apparatus according to  claim 5 , wherein said vacuum space comprises a recess in said at least one member. 
     
     
       7. An apparatus according to  claim 1 , further comprising a plurality of supports defining  constructed and arranged to define a position of said mask perpendicular to its plane. 
     
     
       8. An apparatus according to  claim 7 , wherein each support comprises one of a post and burl. 
     
     
       9. An apparatus according to  claim 5 , wherein said at least one support  member comprises a duct in communication with said vacuum space, said duct being constructed and arranged to evacuate said vacuum space. 
     
     
       10. An apparatus according to  claim 7 , comprising three supports, wherein said three supports are arranged to support said mask proximate the middle of one of its sides and proximate two of its corners, opposite said one of its sides. 
     
     
       11. An apparatus according to  claim 7 , comprising three supports, wherein each support is arranged to support said mask proximate a respective one of its corners. 
     
     
       12. An apparatus according to claim  7 , comprising four supports, wherein each support is arranged to support said mask proximate a respective one of its corners. 
     
     
       13. An apparatus according to  claim 12 , wherein three of said supports are fixed and a fourth one of said supports is movable perpendicular to the plane of the mask and is arranged to provide a desired supporting force. 
     
     
       14. An apparatus according to  claim 13 , wherein said fourth support comprises a spring or gas bearing. 
     
     
       15. An apparatus according to  claim 13 , wherein said fourth support is damped. 
     
     
       16. An apparatus according to  claim 1 , wherein said at least one member is arranged to exert a torsional force on said mask for compensating against gravitational sagging of said mask. 
     
     
       17. An apparatus according to  claim 1 , wherein said at least one compliant member comprises a membrane. 
     
     
       18. An apparatus according to  claim 17 , further comprising a vacuum chamber in a table supporting said at least one member, said vacuum chamber being constructed and arranged to deform said member. 
     
     
       19. An apparatus according to  claim 17 , wherein said at least one member is pre-stressed. 
     
     
       20. An apparatus according to  claim 17 , wherein said at least one member is made of one or more materials selected from: metal, silica, CaF 2 , MgF 2 , BaF 2 , Al 2 O 3  and Zerodur ceramic. 
     
     
       21. An apparatus according to  claim 1 , further comprising a gas bearing for supporting said at least one member. 
     
     
       22. An apparatus according to  claim 1 , further comprising a gas cushion for supporting said at least one member. 
     
     
       23. An apparatus according to  claim 22 , wherein said gas cushion has a thickness in the range of from 5 to 20 μm. 
     
     
       24. A method of manufacturing a device comprising:
 providing a mask bearing a pattern to a first object table;  
 providing a substrate provided with a radiation-sensitive layer to a second object table; and  
 irradiating portions of the mask and imaging irradiated portions of the mask onto target portions of said substrate; and  
 holding said mask, during operation, on said first object table with the aid of at least one compliant member such that said at least one compliant member yields under the weight of the mask to conform substantially to the profile of the mask and supports substantially the entire weight of the mask without a support, under a point of contact between the mask and the compliant member, to support substantially the entire weight of the mask, wherein a portion of said at least one compliant member is in direct contact with said mask and said portion has a stiffness lower than the stiffness of the mask.  
 
     
     
       25. A device manufactured according to the method of  claim 24 . 
     
     
       26. A mask table comprising at least one compliant member for holding a mask such that, when the mask is held by said at least one compliant member, said at least one compliant member yields under the weight of the mask to conform substantially to the profile of the mask and supports substantially the entire weight of the mask without a support, under a point of contact between the mask and the compliant member, to support substantially the entire weight of the mask, wherein a portion of said at least one compliant member is in direct contact with said mask and said portion has a stiffness lower than the stiffness of the mask. 
     
     
       27. An apparatus according to  claim 17 , wherein the membrane supports substantially the entire weight of the mask when the mask is held by said at least one member. 
     
     
       28. A method according to  claim 24 , wherein said at least one compliant member is a membrane. 
     
     
       29. A method according to  claim 28 , wherein the membrane supports substantially the entire weight of the mask when the mask is held with the aid of said at least one member. 
     
     
       30. A method according to  claim 24 , wherein said at least one member comprises a pair of parallel strips. 
     
     
       31. A method according to  claim 24 , further comprising a plurality of supports constructed and arranged to define a position of said mask perpendicular to its plane. 
     
     
       32. A method according to  claim 24 , wherein said at least one member is arranged to exert a torsional force on said mask for compensating against gravitational sagging of said mask. 
     
     
       33. A mask table according to  claim 26 , further comprising a plurality of supports constructed and arranged to define a position of said mask perpendicular to its plane. 
     
     
       34. A mask table according to  claim 26 , wherein said at least one compliant member comprises a membrane. 
     
     
       35. A mask table according to  claim 34 , wherein the membrane supports substantially the entire weight of the mask when the mask is held by said at least one member.