Method and apparatus of electrical field assisted imprinting
View Patent ↗A method and apparatus for performing nanoimprint lithography. When an electric field is applied between the mold and the substrate, various forces can be generated among molds, substrates, and resists. The electrostatic force between the mold and the substrate can serve as an imprinting pressure to press the structured mold into the conformable resist. In addition, the electric field induces additional wetting forces (electrowetting or dielectrophoresis) in a liquid resist, which can assist the flow and filling of the liquid resist into fine structures.
1. A method of forming a patterned surface comprising the steps of:
providing a mold having a molding surface, the mold including a conductive layer;
disposing a substrate having a surface adjacent the molding surface but spaced therefrom by a gap, the substrate including a conductive layer;
disposing within said gap a hardenable or curable liquid;
applying an electric field between the conductive layers to facilitate a flow of said liquid in the gap, to change wetting or filling of said liquid on said molding and substrate surfaces, and to generate an electrostatic force between said mold and said substrate to imprint said liquid; and
hardening or curing the liquid to form the patterned surface.
2. The method of claim 1 wherein said electric field is generated by a time-dependent variable signal having a frequency between 2 Hz and 10 GHz.
3. The method of claim 1 said step of applying an electric field includes applying an alternating current driving signal between said mold conductive layer and said substrate conductive layer.
4. The method of claim 1 wherein said flow is induced by an electro-hydrodynamic wetting force generated at a triple-phase-line defined as an intersection of an ambient gas, the applied liquid and at least one of the substrate and the mold.
5. The method of claim 1 further including the step of temporarily bonding said mold to said substrate with an adhesion layer prior to said application of said electric field.
6. The method of claim 5 wherein said adhesion layer is a chemical glue.
7. The method of claim 1 further including the step of aligning said mold and said substrate prior to applying said electric field.
8. The method of claim 1 wherein said molding surface includes at least one molding feature to imprint said patterned surface.
9. The method of claim 8 wherein said molding surface has at least two molding features spaced apart by less than 200 nanometers.
10. The method of claim 8 wherein said at least one molding feature has a depth in a range from 1 nm to 500 um.
11. The method of claim 1 wherein said flow of liquid has a thickness in the range of 0.1 to 100 μm.
12. The method of claim 1 further including the step of monitoring a size of said gap during said application of said electric field.
13. The method of claim 1 further including the step of selecting said gap size prior to application of said electric field.
14. The method of claim 13 wherein said gap size is selected in response to a size of a feature of said pattern.
15. The method of claim 1 wherein said substrate is a conductor, a semiconductor, an electrically conductive polymer wafer, or a semiconductor-on-insulator.
16. The method of claim 1 wherein said substrate is an insulator, and wherein said conductive layer is disposed on at least one surface thereof.
17. The method of claim 1 wherein said mold conductive layer and said substrate conductive layer define a plurality of isolated electrodes.
18. The method of claim 17 wherein said step of applying said electric field includes selectively activating at least one of said isolated electrodes.
19. The method of claim 17 wherein said step of applying said electric field includes selectively activating said isolated electrodes in a selected sequence.
20. The method of claim 17 wherein said step of applying said electric field includes selectively activating said isolated electrodes in a sequence selected to drive said flow of liquid through said gap and/or to expel air from said gap.
21. The method of claim 20 wherein said flow of liquid is driven in a selected direction through said gap between said mold and said substrate.
22. The method of claim 20 wherein said flow of liquid is driven to a selected position within said gap between said mold and said substrate.
23. The method of claim 1 wherein said liquid is selected from a set of liquids including thermally or UV-curable polymer precursors, nonpolar or polar functional liquids, aqueous or organic solutions, and polymer melts.
24. The method of claim 1 wherein said step of applying said electric field includes varying said electric field during said flow of liquid to facilitate elimination of air bubbles between said mold and said substrate.
25. The method of claim 1 wherein said step of applying said electric field includes varying said electric field during said flow of liquid to regulate a characteristic of said flow of liquid.
26. The method of claim 1 wherein said step of applying said electric field imparts a pressure in said liquid to facilitate air absorption by said liquid within said gap.
27. The method of claim 1 wherein said step of applying said electric field alters the triple phase line of liquid, solid and vapor states of said liquid within said gap.
28. The method of claim 1 wherein said step of disposing said liquid within said gap is implemented by a process selected from a set of disposition processes, including application of liquid droplets, spin coating of the substrate, and dispensing through one or more dispensing tool.
29. The method of claim 1 further including the application of an additional imprinting force to imprint said mold into said liquid, said additional imprinting force selected from a set of forces including an electromagnetic force, an external fluid pressure, an external air pressure, and a mechanical pressure.
30. The method of claim 1 wherein said mold includes a supporting wafer with said conducting layer, and wherein said molding surface bears a set of imprinting features.
31. The method of claim 30 wherein said supporting wafer is composed of a material selected from a set of materials including silicon, silicon oxide, fused silica, quartz, silicon nitride, glass, semiconductors or dielectric substrates.
32. The method of claim 30 wherein said supporting wafer is composed of a material selected from a set of materials including flexible polymeric substrates.
33. The method of claim 1 wherein said mold conductive layer and said substrate conductive layer are each composed of a material selected from a set of materials including metallic materials, doped semiconductors, electrically conductive polymers, or other conductive compounds.
34. The method of claim 1 wherein said molding surface is composed of a dielectric material.
35. The method of claim 1 wherein said molding surface is a surface of said conductive layer.
36. The method of claim 1 wherein said molding surface is disposed on a layer of said mold which is separate from said conductive layer.
37. The method of claim 1 wherein said molding surface defines at least one two-dimensional, three-dimensional, or gradient topographical structure.
38. The method of claim 1 wherein said molding surface defines a plurality of isolated pattern domains for imprinting said patterned surface.