Substrate holder and method of manufacturing a substrate holder
An object holder for a lithographic apparatus has a main body having a surface. A plurality of burls to support an object is formed on the surface or in apertures of a thin-film stack. At least one of the burls is formed by laser-sintering. At least one of the burls formed by laser-sintering may be a repair of a damaged burl previously formed by laser-sintering or another method.
1. A method of repairing an object holder for use in a lithographic apparatus, the object holder having a plurality of burls to support an object and having a damaged burl having a rough upper surface, the method comprising:
grinding the rough upper surface of the damaged burl so as to provide a smooth surface; and
rebuilding the damaged burl to at least its original shape and/or height by adding a layer on top of the smooth surface such that its height is higher than the height of the plurality of burls.
2. The method of claim 1 , wherein the adding the layer on top of the smooth surface comprises laser-sintering.
3. The method of claim 2 , wherein the laser-sintering comprises:
applying a layer of powder on top of the smooth surface; and
selectively irradiating the layer of powder with a radiation beam so as to cause at least partial melting of the powder at irradiated locations.
4. The method of claim 2 , wherein the laser-sintering comprises:
irradiating a location on the smooth surface; and
jetting powder at the irradiated location.
5. The method of claim 1 , wherein the rebuilding the damaged burl comprises laser-sintering.
6. The method of claim 1 , wherein the rebuilding the damaged burl comprises polishing the damaged burl to level match the height of the plurality of burls.
7. The method of claim 1 , further comprising providing a temporary protective coating to cover the plurality of burls during the grinding of the rough upper surface of the damaged burl.
8. The method of claim 1 , further comprising cleaning and/or pre-treating the smooth surface.
9. The method of claim 8 , wherein the smooth surface is cleaned with ozone.
10. The method of claim 8 , wherein the smooth surface is pre-treated by application of a primer.
11. The method of claim 1 , wherein the rebuilt burl comprises at least one material selected from the group consisting of: Ti, Si, fused silica, cordierite, diamond-like carbon, SiC, SiO 2 , AlN, TiN and CrN.
12. The method of claim 1 , wherein the rebuilt burl comprises a matrix material and particles embedded in the matrix material.
13. The method of claim 1 , wherein the rebuilt burl comprises a first layer of a first material and a second layer of a second material that is different from the first material.
14. The method of claim 13 , wherein the first and second materials are different in a property or a component.
15. The method of claim 1 , wherein the object is a substrate or a patterning device.
16. A method of repairing an object holder for use in a lithographic apparatus, the object holder having a plurality of burls to support an object and having a damaged burl having a rough upper surface, the method comprising:
grinding the rough upper surface of the damaged burl so as to provide a smooth surface; and
rebuilding the damaged burl to at least its original shape and/or height by adding a layer on top of the smooth surface by laser-sintering.
17. The method of claim 16 , wherein the laser-sintering comprises:
applying a layer of powder on top of the smooth surface; and
selectively irradiating the layer of powder with a radiation beam so as to cause at least partial melting of the powder at irradiated locations.
18. The method of claim 16 , wherein the laser-sintering comprises:
irradiating a location on the smooth surface; and
jetting powder at the irradiated location.
19. The method of claim 16 , wherein the rebuilt burl comprises a first layer of a first material and a second layer of a second material that is different from the first material.
20. The method of claim 16 , wherein the rebuilt burl comprises a matrix material and particles embedded in the matrix material.