Superstrate and method of making it

1. A superstrate comprising a superstrate blank and a coating overlying an outer surface of the superstrate blank, wherein

the superstrate blank comprises a central region and a tapered edge region;

the tapered edge region of the superstrate blank has an average taper angle of not greater than 8 degrees relative to a radial direction of the superstrate blank;

the coating is overlying the central region and at least a portion of the tapered edge region of the superstrate blank; and

the superstrate is configured for planarizing a top surface of a formable material positioned on a substrate when bringing the superstrate in contact with the formable material.

2. The superstrate of claim 1 , wherein the coating comprises an edge bead within the tapered edge region, and an apex of the edge bead is below a plane of an outer surface of the coating in the central region of the superstrate.

3. The superstrate of claim 1 , wherein a surface area ratio Sc:St is at least 15, with Sc being a surface area of the central region and St being a surface area of the tapered edge region.

4. The superstrate of claim 1 , wherein a length of the tapered edge region (T 1 ) in radial direction is at least 1.0 mm.

5. The superstrate of claim 1 , wherein the superstrate blank has an average thickness within the central region of at least 100 microns and not greater than 5000 microns.

6. The superstrate of claim 1 , wherein the coating has an average thickness within the central region of at least 0.1 microns and not greater than 10 microns.

7. The superstrate of claim 1 , wherein the coating is transparent to an actinic radiation.

8. A method of forming a planar layer of a formable material on a substrate with a superstrate, comprising:

preparing a superstrate, the superstrate comprising a superstrate blank and a coating overlying an outer surface of the superstrate blank, wherein

the superstrate blank comprises a central region and a tapered edge region,

the tapered edge region of the superstrate blank has an average taper angle of not greater than 8 degrees, relative to a radial direction of the superstrate blank

and the coating overlies the complete central region and at least a portion of the tapered edge region of the superstrate blank;

bringing the superstrate into contact with the formable material on the substrate;

curing the formable material to form the planar layer; and

separating the superstrate from the planar layer.

9. The method of claim 8 , wherein the coating is applied by spin coating.

10. The method of claim 9 , wherein the spin coating comprises forming of an edge bead within the tapered edge region.

11. The method of claim 10 , wherein an apex of the edge bead is below a plane of an outer surface of the coating in the central region of the superstrate.

12. The method of claim 10 , further comprising removing of the edge bead.

13. The method of claim 8 , wherein a surface area ratio Sc:St of the superstrate blank is at least 15, with Sc being a surface area of the central region and St being a surface area of the tapered edge region.

14. The method of claim 9 , wherein the spin coating does not include forming of an edge bead on the superstrate blank.

15. The method of claim 8 , wherein a length of the tapered edge region (T 1 ) in radial direction is at least 1.0 mm.

16. The method of claim 8 , wherein the coating has an average thickness within the central region of at least 0.1 microns and not greater than 10 microns.

17. A method of manufacturing an article comprising:

applying a layer of a formable material on a substrate;

bringing the formable material into contact with a superstrate, wherein the superstrate comprises a superstrate blank and a coating overlying an outer surface of the superstrate blank, and wherein

the superstrate blank comprises a central region and a tapered edge region;

the tapered edge region of the superstrate blank has an average taper angle of not greater than 8 degrees relative to a radial direction of the superstrate blank;

the coating is overlying the complete central region and at least a portion of the tapered edge region of the superstrate blank;

curing the formable material to form the planar layer;

removing the superstrate from the planar layer; and

processing the substrate with the planar layer to make the article.

18. A system for planarizing a formable material, comprising:

a superstrate coupled to a superstrate holder; and

a formable material positioned on a substrate,

wherein the superstrate comprises a superstrate blank and a coating overlying an outer surface of the superstrate blank, wherein the superstrate blank comprises a central region and a tapered edge region; the tapered edge region of the superstrate blank has an average taper angle of not greater than 8 degrees relative to a radial direction of the superstrate blank; and the coating is overlying the central region and at least a portion of the tapered edge region of the superstrate blank; and

wherein the superstrate is positioned above a top surface of the formable material and configured for planarizing the top surface of the formable material.