Substrate holder, a lithographic apparatus and method of manufacturing devices
A substrate holder for use in a lithographic apparatus and configured to support a substrate, the substrate holder including: a main body having a main body surface; and a plurality of burls projecting from the main body surface; wherein each burl has a distal end configured to engage with the substrate; the distal ends of the burls substantially conform to a support plane whereby a substrate can be supported in a substantially flat state on the burls; a frictional force between the distal end of each burl and a substrate engaged therewith arises in a direction parallel to the support plane in the event of a relative movement of the substrate and substrate holder in the direction; and distal end surfaces of the burls are provided with a release structure configured so that the frictional force is less than would arise in the absence of the release structure.
1. A substrate holder for use in a lithographic apparatus and configured to support a substrate, the substrate holder comprising:
a main body having a main body surface; and
a plurality of burls projecting from the main body surface, wherein
each burl has a distal end configured to engage with the substrate;
the distal ends of the burls substantially conform to a support plane and are configured for supporting a substrate;
a frictional force between the distal end of each burl and a substrate engaged therewith arises in a direction parallel to the support plane; and
distal end surfaces of the burls are provided with a release structure configured so that the frictional force is less than would arise in the absence of the release structure, the release structure comprising a recess in the distal end surface of each burl, the recess comprising a main recess part and a plurality of channels which lead from the main recess part to the peripheral edge of the distal end surface, wherein the plurality of channels intersect a side wall surface of the main recess part.
2. A substrate holder according to claim 1 , wherein the recess has an area in the range of from ¼ to ¾ of the total area of the distal end surface.
3. A substrate holder according to claim 1 , wherein the recess has a depth in the range of from 10 nm to 40 nm.
4. A substrate holder according to claim 1 , wherein the main recess part has a shape in plan selected from the group consisting of circle, square, oval, star, and cross.
5. A substrate holder according to claim 1 , wherein the release structure comprises a layer of diamond-like carbon applied to the distal end surfaces of the burls.
6. A substrate holder according to claim 5 , wherein the layer of diamond-like carbon has a thickness of greater than about 1 μm.
7. A substrate holder according to claim 5 , wherein the layer of diamond-like carbon has a thickness of less than about 2 μm.
8. A substrate holder according to claim 5 , wherein the layer of diamond-like carbon comprises at least one additive selected from the group consisting of Si, N, Mo and Fl.
9. A lithographic apparatus for projecting an image onto a substrate, the lithographic apparatus comprising:
the substrate holder according to claim 1 ; and
a clamp system configured to clamp a substrate to the substrate holder.
10. A lithographic apparatus according to claim 9 , wherein the clamp system is configured to exert, in use, a clamping force urging the substrate toward the substrate holder, the clamping force being sufficiently strong that the substrate contacts the burl in the area of the main recess part when the clamping force is in effect.
11. A method of manufacturing devices using a substrate holder comprising:
a main body having a main body surface; and
a plurality of burls projecting from the main body surface, wherein
each burl has a distal end configured to engage with the substrate;
the distal ends of the burls substantially conform to a support plane and are configured for supporting a substrate;
a frictional force between the distal end of each burl and a substrate engaged therewith arises in a direction parallel to the support plane; and
distal end surfaces of the burls are provided with a release structure configured so that the frictional force is less than would arise in the absence of the release structure, the release structure comprising a recess in the distal end surface of each burl, the method comprising:
loading a substrate onto the substrate holder;
allowing a deformation of the substrate to relax;
engaging a clamp system to clamp the substrate to the substrate holder, wherein the clamp system exerts a clamping force urging the substrate toward the substrate holder, the clamping force sufficiently strong that the substrate contacts the burl in the area of the recess when the clamping force is in effect; and
exposing a pattern onto the substrate.
12. A method according to claim 11 , wherein the release structure comprises a single recess in the distal end surface of each burl.
13. A method according to claim 11 , wherein the recess has an area in the range of from ¼ to ¾ of the total area of the distal end surface.
14. A method according to claim 11 , wherein a part of the recess extends to a peripheral edge of the distal end surface.
15. A method according to claim 14 , wherein the recess comprises a main recess part and a plurality of channels which lead from the main recess part to the peripheral edge of the distal end surface.
16. A method according to claim 11 , wherein the recess has a depth in the range of from 10 nm to 40 nm.
17. A method according to claim 11 , wherein the release structure comprises a layer of diamond-like carbon applied to the distal end surfaces of the burls.
18. An object holder configured for an object processing tool and configured to support an object, the object holder comprising:
a main body having a main body surface; and
a plurality of burls projecting from the main body surface, wherein
each burl has a distal end configured to engage with the object;
the distal ends of the burls substantially conform to a support plane and are configured for supporting an object;
a frictional force between the distal end of each burl and an object engaged therewith arises in a direction parallel to the support plane; and
distal end surfaces of the burls are provided with a release structure configured so that the frictional force is less than would arise in the absence of the release structure, the release structure comprising a recess in the distal end surface of each burl, the recess comprising a main recess part and a plurality of channels which lead from the main recess part to the peripheral edge of the distal end surface, wherein the plurality of channels intersect a side wall surface of the main recess part.
19. The object holder of claim 18 , wherein the object is a patterning device and the object processing tool is a lithographic apparatus.
20. The object holder of claim 18 , wherein the object is a semiconductor substrate and the object processing tool is a metrology or inspection apparatus.