US20060177535A1 - Imprint lithography template to facilitate control of liquid movement - Google Patents

Abstract

The present invention is directed to a template that features a control surface extending from a periphery of a mold toward a recessed surface of the template forming an oblique angle between a portion of the control surface disposed proximate to the periphery.

Description

CROSS-REFERENCE TO RELATED APPLICATION
• The present application is a divisional application of U.S. patent application Ser. No. 11/051,533 entitled “Imprint Lithography Template to Control Extrusion of a Liquid from a Desired Region on a Substrate,” naming inventors Edward B. Fletcher, Ian M. McMackin, Michael N. Miller, Nicholas A. Stacey, Wesley Martin, Frank Y. Xu, Christopher J. Mackay and Van N. Truskett, filed Feb. 4, 2005, which is incorporated herein by reference.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
• The United States government has a paid-up license in this invention and the right in limited circumstance to require the patent owner to license others on reasonable terms as provided by the terms of 70NANB4H3012 awarded by National Institute of Standards (NIST) ATP Award.
BACKGROUND OF THE INVENTION
• The field of the invention relates generally to micro-fabrication techniques. More particularly, the present invention is directed to a template to control movement of a liquid suitable for imprint lithography.
• The prior art is replete with examples of exemplary micro-fabrication techniques. One particularly well-known micro-fabrication technique is imprint lithography. Imprint lithography is described in detail in numerous publications, such as United States published patent application 2004/0065976 filed as U.S. patent application Ser. No. 10/264,960, entitled “Method and a Mold to Arrange Features on a Substrate to Replicate Features having Minimal Dimensional Variability”; United States published patent application 2004/0065252 filed as U.S. patent application Ser. No. 10/264,926, entitled “Method of Forming a Layer on a Substrate to Facilitate Fabrication of Metrology Standards”; and United States published patent application 2004/0046271 filed as U.S. patent application Ser. No. 10/235,314, entitled “Method and a Mold to Arrange Features on a Substrate to Replicate Features having Minimal Dimensions Variability”; all of which are assigned to the assignee of the present invention. The fundamental imprint lithography technique as shown in each of the aforementioned published patent applications includes formation of a relief pattern in a polymerizable layer and transferring a pattern corresponding to the relief pattern into an underlying substrate. To that end, a template, having a mold, is employed. The mold is spaced-apart from, and in superimposition with, the substrate with a formable liquid present therebetween. The liquid is patterned and solidified to form a solidified layer that has a pattern recorded therein that is conforming to a shape of a mold. The substrate and the solidified layer may then be subjected to processes to transfer, into the substrate, a relief image that corresponds to the pattern in the solidified layer.
• One manner in which to locate the polymerizable liquid between the template and the substrate is by depositing the liquid on the substrate as one or more droplets, referred to as a drop dispense technique. Thereafter, the polymerizable liquid is concurrently contacted by both the template and the substrate to spread the polymerizable liquid over the surface of the substrate. It is desirable to have the liquid confined to an area of the substrate in superimposition with the mold.
• Thus, there is a need to provide greater control over movement of a liquid during imprint lithographic processes.
SUMMARY OF THE INVENTION
• The present invention is directed to a template that features a control surface extending from a periphery of a mold toward a recessed surface of the template forming an oblique angle between a portion of the control surface disposed proximate to the periphery. In this fashion, a capillary force gradient may be created between imprinting material and the surface of the template facing the imprinting material. This provides greater control over a quantity of imprinting material extruding from a volumetric gap defined between the mold and a region of a substrate in superimposition. As a result, formation of undesirable artifacts during imprint lithography is reduced, if not avoided. These and other embodiments of the present invention are discussed more fully below.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a cross-sectional view of a template, having disposed opposite to a substrate with imprinting material disposed therebetween, in accordance with the prior art;
• FIG. 2 is a cross-sectional view of a solidified imprinting layer formed upon the substrate employing the template shown inFIG. 1, having a conformal layer disposed thereon in accordance with the prior art;
• FIG. 3 is a simplified top-down view of the conformal layer shown inFIG. 2, in accordance with the prior art;
• FIG. 4 is a cross-sectional view of a template, having disposed opposite to a substrate with imprinting material disposed therebetween, in accordance with the present invention;
• FIG. 5 is a cross-sectional view of a template shown inFIG. 4 in accordance with a first alternate embodiment of the present invention;
• FIG. 6 is a cross-sectional view of a template shown inFIG. 4 in accordance with a second alternate embodiment of the present invention;
• FIG. 7 is a cross-sectional view of a template shown inFIG. 4 in accordance with a fifth alternate embodiment of the present invention;
• FIG. 8 is a cross-sectional view of a template shown inFIG. 4 in accordance with a sixth alternate embodiment of the present invention; and
• FIG. 9 is a cross-sectional view of a template shown inFIG. 4 in accordance with a seventh alternate embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
• Referring toFIG. 1, atemplate10 is shown in contact withimprinting material12, withimprinting material12 being disposed between amold14 andsubstrate16 in furtherance of patterning imprinting material. To that end,mold14 is spaced-apart fromsubstrate16 and imprintingmaterial12 substantially fills a volumetric gap defined betweenmold14 and aregion18 ofsubstrate16 in superimposition therewith. Thereafter,imprinting material12 is solidified by exposing the same to an actinic component. In this manner, the shape of asurface20 ofmold14, facingimprinting material12, is recorded therein by formation ofsolidified imprinting layer22, shown inFIG. 2.
• Referring toFIGS. 1 and 2,surface20 ofmold14 is patterned by inclusion of a plurality ofprotrusions24 andrecessions26. The apex portion of each ofprotrusions24 lies in a common plane, P. It should be understood, however, thatsurface20 may be substantially smooth, withoutprotrusions24 andrecessions26, if not planar.
• The actinic component employed to solidifyimprinting material12 may be any known substance, depending upon the composition ofimprinting material12. Exemplary compositions forimprinting material12 are disclosed in U.S. patent application Ser. No. 10/763,885, filed Jan. 24, 2003, entitled “Materials and Methods for Imprint Lithography,” which is incorporated by reference. As a result, the actinic component employed is typically ultraviolet wavelengths, andmold14, not theentire template10, is fabricated from fused silica. However, other actinic components may be employed, e.g., thermal, electromagnetic and the like.
• Imprinting material12 may be deposited upon eithersubstrate16 and/ortemplate10 employing virtually any known technique, dependent upon the composition employed. Such deposition techniques include but are not limited to, chemical vapor deposition (CVD), physical vapor deposition (PVD) spin-coating, and drop dispense techniques. After formation ofsolidified imprinting layer22,mold14 is separated therefrom, andsolidified imprinting layer22 remains onsubstrate16.Solidified imprinting layer22 includesresidual regions28 having a thickness t₁andprojections30 having a thickness t₂, with t₁being 10 nm or greater and t₂being 40 nm or greater. Control of the dimensions of features recorded insolidified imprinting layer22 is dependent, in part, upon the volume ofimprinting material12 in superimposition withregion18. As a result, attempts have been undertaken to confineimprinting material12 to the volumetric gap during imprinting processes.
• One attempt to confineimprinting material12 to the volumetric gap includes formingmold14 ontemplate10 as a mesa. To that end,mold14 extends from arecessed surface21 oftemplate10 and terminates in plane.Sidewall23 functions to assist confiningimprinting material12 within the volumetric gap due to the lack of capillary attraction betweenimprinting material12 andmold14 outside the volumetric gap. Specifically,sidewall23 is provided with sufficient length to reduce the probability that capillary attraction betweenrecessed surface21 andimprinting material12 occurs.
• Occasionally during the imprinting process,imprinting material12 may extrude beyond the volumetric gap so as to lie outside ofregion18 and/orsurface60. This may be due to, inter alia, fluid pressure generated inimprinting material12 while being compressed betweensubstrate16 andmold14. Further, the fluid pressure causes a sufficient quantity ofimprinting material12 to extrude beyond the volumetric gap so that capillary attraction between this material andrecessed surface21 occurs. As a result, formed, proximate to the periphery ofregion18, are extrusions32. Extrusions32 have a thickness t₃that may be several orders of magnitude larger than thicknesses t₁and t₂, depending upon the spacing between surface34 andregion18. For example, thickness t₃may be 2 μm-15 μm. The presence ofextrusions32 may be problematic. For example, imprintingmaterial12 contained inextrusions32 may not completely cure when exposed to the actinic component. This may result inimprinting material12 accumulating at aperiphery36 ofmold14. Additionally, upon separation ofmold14 from solidified imprintinglayer22, imprintingmaterial12 inextrusions32 may spread over the remaining portions ofsubstrate16 lying outside of the volumetric gap. Additionally, extrusions32 may become cured, which can result in same remaining onsubstrate16 as part of solidifiedimprinting layer22. Any of the aforementioned effects ofextrusions32 can generate unwanted artifacts during subsequent imprinting processes.
• Referring toFIGS. 2 and 3, wereextrusion32 partially cured, for example, control of the thickness of subsequently disposed layers becomes problematic. This is shown by formation ofmulti-layered structure38 resulting from the deposition of aconformal layer40 upon solidifiedimprinting layer22. In the present example,conformal layer40 is formed employing spin-on techniques as discussed in U.S. patent application Ser. No. 10/789,319, filed on Feb. 27, 2004 entitled “Composition for an Etching Mask Comprising a Silicon-Containing Material.” The presence ofextrusions32, however, reduces the planarity of thesurface42 ordinarily expected from spin-on deposition ofconformal layer40. The presence ofextrusions32 results in the formation of deleterious artifacts, such as thickness variations, inconformal layer40. These deleterious artifacts present as protrusions insurface42, are generally referred to ascomets44.Comets44 are, typically, undesirable artifacts, because the same produce peaks46 andtroughs48 insurface42. As a result,surface42 is provided with a roughness that hinders patterning very small features. Similar roughness problems in subsequently formed surfaces arise in the presence of artifacts generated byextrusions32.
• Referring toFIG. 4, to avoid the deleterious artifacts, the present invention reduces, if not prevents, an amount of imprintingmaterial12 from extruding outside the volumetric gap. To that end, atemplate50 includes amold52 layer and both are substantially the same as discussed above with respect totemplate10 andmold14, excepting thattemplate50 includes a capillary force control (CFC)surface54.CFC surface54 extends betweenmold52 andsidewall56 forming an angle Φ with respect to plane P. CFC surface54 functions to control, if not prevent, a quantity ofimprinting material12 from extruding outside the volumetric gap by avoiding an orthogonal angle being formed betweenperiphery53 ofmold52 andCFC surface54. Specifically, it was recognized that a certain quantity ofimprinting material12 may extend beyond the volumetric gap defined betweenregion18 andsurface60 in superimposition therewith. With this realization, implemented is control, rather than avoidance, of imprinting material extruding from the volumetric gap. To that end,CFC surface54 is selected to produce a gradient of capillary forces proximate toperiphery53, with imprintingmaterial12 that comes in contact therewith. This is achieved, in part, by forming an oblique angle Φ betweenCFC surface54 andperiphery53.
• CFC surface54 extends upwardly away from plane P and outwardly away fromregion18, producing a linear increase in the distance with respect tosubstrate16 to a maximum distance d and without having to vary the volumetric gap, i.e., the volume of the volumetric gap remains constant. The result of the linear increase in the distance of separation betweentemplate50 andsubstrate16 produces a force gradient in the capillary forces generated by contact betweenimprinting material12 andCFC surface54. Specifically, thefarther imprinting material12 extrudes from the volumetric gap, the greater the distance d betweenCFC surface54 andsubstrate16; hence, the lesser the capillary forces. By selecting the appropriate angle Φ and length ofCFC surface54, the amount of a givenimprinting material12, subjected to a given compression force betweensurface60 andregion18, extruding beyond the volumetric gap may be controlled. This, in turn, facilitates control over the size of extrusions and/or the quantity ofuncured imprinting material12 that may spread to other regions ofsubstrate16 during separation ofmold52, after solidification ofimprinting material12 as discussed above. It is desired, however that the aspect ratio of width and height ofCFC surface54, as defined by the length and angle Φ be on the order of the protrusions and projections.
• It should be understood that gradually decreasing capillary forces between imprintingmaterial12 andtemplate50 may be achieved by providingCFC surface54 with a variety of shapes. For example,CFC surface54 may be configured so that the distance between the surfaces oftemplate50 andsubstrate16 vary exponentially, while maintaining a constant volumetric gap. To that end,CFC surface54 may have a concave shape shown assurface154, inFIG. 5, or a convex shape, shown assurface254 inFIG. 6, with the angle Φ formed betweenperiphery53 and one ofsurfaces154 and254 being an oblique angle. The rate of curvature ofsurfaces154 and254 are established such that the quantity ofimprinting material12 extending beyondregion18 remains within desired parameters.
• In a further embodiment, capillary force control (CFC)surface554 extends between plane P and recessedsurface547, shown inFIG. 7, i.e., without the presence ofsidewall23 as shown inFIG. 4. To that end,CFC surface654 may extend between plane P and recessedsurface657 so as to have a concave shape, shown inFIG. 8 or a convex shape, shown assurface757 extending between plane P and recessed surface747 inFIG. 9.
• Referring again toFIG. 1, in a further embodiment, to further improve the control of extrusion of imprintingmaterial12 beyondregion18, the wetting characteristics ofCFC surface54, and/or mesa sidewalls23 and/or recessedsurface21 may be reduced, or minimized, when compared to the wetting characteristics ofsurface20. In this manner, the surfaces oftemplate10 facingsubstrate16 are provided with differing wetting characteristics. One manner in which to achieve this is to establish the appropriate surface energies, for a givenimprinting material12, among the various surfaces oftemplate10. For example, it is desired to establishsurface20 to have the lowest surface energy characteristics.
• Referring toFIG. 4, implementing these principles in conjunction withtemplate50 may facilitate greater control over the extrusion of imprintingmaterial12 outside of the volumetric gap. For example, the desired surface energy forsurface54, ormesa sidewall55 and recessedsurface57, may be established based upon the surface tension of imprintingmaterial12 and the surface energy of patternedsurface60 ofmold52. It should be understood that it is not necessary that each ofCFC surface54,mesa sidewall55 and recessedsurface57 have the same surface energy.
• One manner in which to establish the surface energy ofCFC surface54,mesa sidewall55 and recessedsurface57 employs application of a low surface energy coating formed by methods including, but not limited to, chemical vapor deposition (CVD), physical vapor deposition (PVD), thermal oxidation, and ion implantation. An exemplary technique, to that end, may include application of fluorine-containing materials, such as electroless nickel coating containing fluorinated particles.
• Moreover, a fluorinated composition employed for the low surface energy coating may be dissolved or dispersed in a solvent or other suitable fluid which may be applied to the desired surfaces oftemplate50 employing one or more of a plurality of methods: dipping, spraying, and brushing. Additional processing may improve the density of the low surface energy coating and increase the bonding of the low surface energy coating to improve the durability of the same. Alternatively, a fluorine-containing compound may be left upon the desired surfaces oftemplate50 by exposing the same to fluorine-containing etchant chemistries.
• An exemplary fluorine-containing composition includes a solution comprised of a hydrofluoroether solvent and tridecafluoro-1,1,2,2,-tetrahydrooctyltrichlorosilane (FOTS). The solution may be dispensed via a pipette upon one or more ofCFC surface54,mesa sidewall55 and recessedsurface57. The ratio of FOTS to hydrofluoroether is approximately 1 microliter of FOTS per 3.5 milliliters of hydrofluoroether. The component hydrofluoroether is available from 3M located in St. Paul, Minn. under the trade name HFE-7100DL. After application of FOTS, the template may be dried employing nitrogen. Another fluorine-containing composition may include a solution of a mono-functional silane having a perfluoropolyether backbone or a di-functional silane having a perfluoropolyether backbone in a fluorinated solvent.
• Other materials and processes may be employed to vary surface energies of various surfaces oftemplate50. For example, a sol-gel layer may be formed uponCFC surface54,mesa sidewall55 and recessedsurface57. Additionally, one or more ofCFC surface54,mesa sidewall55 and recessedsurface57 may be provided with a roughened surface, for example, providing the same with a fractal structure, which is subsequently coated with a highly ordered low surface energy self-assembled monomer layer, as disclosed by Shibuichi et al. in SUPER WATER-AND OIL-REPELLANT SURFACE RESULTING FROM FRACTAL STRUCTURE, Journal of Colloid and Interface Science 208, 287-294 (1998). To that end, one or more ofCFC surface54,mesa sidewall55 and recessedsurface57 would be subjected to an anode oxidation method as disclosed therein and then coated with a composition containing long chain fluorinated silanes, such as, one of 1H,1H,2H,2H-perfluorooctyltrichlorosilane, 1H,1H,2H,2H-perfluorodecyl phosphate and the like. Monolayers formed from these structures have been shown to exhibit surface energies of approximately 6 mN/m.
• With the aforementioned coatings on one or more ofCFC surface54,mesa sidewall55 and recessedsurface57, along with the various shapes with which CFC surface54 may be configured, control over the quantity ofimprinting material12 extruding from the volumetric gap may be greatly facilitated. For example, for a given quantity ofimprinting material12 and aspect ratio ofrecessions62 it may be possible to arrange the relative surface energies ofCFC surface54,mesa sidewall55 and recessedsurface57, as well as the dimensions thereof, whereby a resulting flow velocity of imprintingmaterial12 would causerecessions62 to be filled withimprinting material12, before any, or a greater than desired amount of, imprintingmaterial12 extrudes outside the volumetric gap. Thus, theimprinting material12 may be cured while minimizing the quantity ofuncured imprinting material12 that remains and/or the dimension of any extrusions formed.
• In a further embodiment, a further control over the quantity of imprinting material extruding outside ofregion18 is achieved by exposing the same to an oxygen-rich fluid environment. Specifically, by directing a stream of oxygen-rich fluid directed toCFC surface54,mesa sidewall55 and recessedsurface57, imprintingmaterial12 disposed thereon will be prevented from curing. Further, exposure to a stream of oxygen may facilitate evaporation of imprintingmaterial12 upon which the fluid stream impinges. Currently, theenvirons surrounding template50 are saturated with helium to prevent trapping of air inimprinting material12. However, prior to exposingimprinting layer12 to actinic radiation, the stream of oxygen-rich fluid may be introduced, with or without interrupting the supply of helium. Furthermore, employing the aforementioned helium flow may facilitate in varying a shape of an edge of the cured portion ofimprinting material12 with respect to theCFC surface54, shown inFIG. 4, by varying the time of employment of the helium flow with respect to the imprinting process.
• The embodiments of the present invention described above are exemplary. Many changes and modifications may be made to the disclosure recited above, while remaining within the scope of the invention. Therefore, the scope of the invention should not be limited by the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.

Claims (20)

1. A template comprising:

a mold having a periphery lying in a plane;

a recessed surface spaced-apart from said plane; and

a control surface extending from said periphery toward said recessed surface, with an oblique angle being defined between a portion of said control surface disposed proximate to said periphery and said plane.

2. The template as recited inclaim 1 further including a sidewall with said control surface extending between said sidewall and said periphery and said sidewall extending between said control surface and said recessed surface.

3. The template as recited inclaim 1 wherein said control surface substantially surrounds said mold.

4. The template as recited inclaim 1 wherein said control surface terminates at said recessed surface.

5. The template as recited inclaim 1 wherein said control surface has an arcuate shape.

6. The template as recited inclaim 1 wherein said control surface has a linear shape.

7. The template as recited inclaim 1 wherein said control surface has a concave shape.

8. The template as recited inclaim 1 wherein said control surface has a convex shape.

9. The template as recited inclaim 1 further comprising a mesa wall surface positioned between said recessed surface and said control surface, with said sidewall surface extending orthogonally to said recessed surface.

10. The template as recited inclaim 1 further wherein said mold has a surface energy associated therewith that is greater than a surface energy of said control surface.

11. A template comprising:

a mold having a periphery lying in a plane;

a recessed surface spaced-apart from said plane;

a sidewall surface; and

a control surface extending between said periphery and said sidewall surface, with an oblique angle being defined between a portion of said control surface disposed proximate to said periphery and said plane, said sidewall surface extending between said control surface and said recessed surface, with said recessed surface extending orthogonally to said sidewall surface.

12. The template as recited inclaim 10 wherein said control surface substantially surrounds said mold.

13. The template as recited inclaim 10 wherein said control surface terminates at said recessed surface.

14. The template as recited inclaim 10 wherein said control surface has an arcuate shape.

15. The template as recited inclaim 10 wherein said control surface has a linear shape.

16. The template as recited inclaim 10 wherein said control surface has a concave shape.

17. The template as recited inclaim 10 wherein said control surface has a convex shape.

18. A template comprising:

a mold having a periphery lying in a plane;

a recessed surface spaced-apart from said plane; and

a control surface extending from said periphery toward said recessed surface, with an oblique angle being defined between a portion of said control surface disposed proximate to said periphery and said plane, with said mold has a surface energy associated therewith that is greater than a surface energy of said control surface.

19. The template as recited inclaim 18 wherein said control surface has a shape associated therewith selected from a set of shapes consisting essentially of a linear shape, a concave shape and a convex shape.

20. The template as recited inclaim 18 further including a sidewall with said control surface extending between said sidewall and said periphery and said sidewall extending between said control surface and said recessed surface, with said sidewall and said recessed surfaces each having a surface energy associated therewith that is less than a surface energy of said mold.

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