US20050160934A1 - Materials and methods for imprint lithography - Google Patents

Abstract

One embodiment of the present invention relates to an imprinting material for imprint lithography that includes the surfactant 3M™ Novec™ Fluorosurfactant FC-4432, and another embodiment of the present invention relates to a method for imprint lithography that uses the imprinting material.

Description

TECHNICAL FIELD OF THE INVENTION
• One or more embodiments of the present invention relate generally to imprint lithography. In particular, one or more embodiments of the present invention relate to materials and methods for imprint lithography.
BACKGROUND OF THE INVENTION
• Micro-fabrication involves the fabrication of very small structures, for example, and without limitation, structures having features on the order of micro-meters or smaller. One area in which micro-fabrication has had a sizeable impact is in processing of integrated circuits. As the semiconductor processing industry continues to strive for larger production yields while increasing the circuits per unit area formed on a substrate, micro-fabrication becomes increasingly important since micro-fabrication provides greater process control while allowing a reduction in the minimum feature dimension of the structures formed. Other areas of development in which micro-fabrication have been employed include biotechnology, optical technology, mechanical systems and the like.
• An exemplary micro-fabrication technique is disclosed in U.S. Pat. No. 6,334,960 to Willson et al. In particular, the Willson et al. patent discloses a method of imprint lithography to form a relief pattern in a structure. The method includes providing a substrate having a transfer layer (typically spin-coated), and covering the transfer layer, in turn, with a low viscosity, polymerizable (typically UV curable) fluid composition (typically in the form of droplets). The method further includes mechanically contacting an imprint template or mold having a relief structure with the polymerizable fluid composition wherein the polymerizable fluid composition fills a gap between the imprint template and the substrate and fills the relief structure of the imprint template. Next, the method includes subjecting the polymerizable fluid composition to conditions to solidify and to polymerize the same (typically, exposing the polymerizable fluid composition to UV to crosslink it), thereby forming a solidified polymeric material on the transfer layer that contains a relief structure complimentary to that of the imprint template. Next, the method includes separating the imprint template from the substrate to leave solid polymeric material on the substrate, which solid polymeric material includes a relief pattern in the form of the complimentary relief structure. Next, the solidified polymeric material and the transfer layer are subjected to an environment to selectively etch the transfer layer relative to the solidified polymeric material to form a relief image in the transfer layer.
• The following issues that relate to selective adhesion of the solidified polymeric material to different surfaces are typically considered when one develops a method and/or a material useful in forming fine-feature relief patterns in the solidified polymeric material. First, the solidified polymeric material ought to adhere well to the transfer layer on the substrate, and second, it ought to be easily released from the surface of the imprint template. These issues are typically referred to as release characteristics and selective/preferential adhesion, and if they are satisfied, the relief pattern recorded in the solidified polymeric material will not be distorted during separation of the imprint template from the substrate. To improve release characteristics, Willson et al. teaches forming a release layer on the surface of the imprint template, which release layer is typically hydrophobic and/or has low surface energy. Such a release layer will provide a weak boundary layer between the imprint template and the solidified polymeric material. This type of release layer is referred to, for purposes of the present discussion, as an a priori release layer, i.e., a release layer that is solidified to the surface of the imprint template.
• Another prior art approach to improving the release characteristics is described by Bender et al. in “Multiple Imprinting in UV-based Nanoimprint Lithography: Related Material Issues,”Microeletronic Engineering61-62 (2002), pp. 407-413. Specifically, Bender et al. utilizes an imprint template having an a priori release layer in conjunction with a fluorine-containing UV curable material. To that end, a UV curable layer is applied to a substrate by spin-coating a 200 cps UV curable fluid to form a UV curable layer. The UV curable layer is enriched with fluorine groups to improve its release characteristics.
• A priori release layers, however, typically have a limited operational life. As a result, a single imprint template needs to be coated multiple times with an a priori release layer during imprint processing. This can result in several hours of down-time for a given imprint template, thereby reducing throughput. Additionally, the molecular structure of the a priori release layer may limit the minimization of the minimum feature dimension that is printed.
• One measure of imprint lithography quality relates to feature filling. As is well known, sufficient wetting, along with other factors, ensures feature filling, and thereby prevents voids. To test one imprint lithography method and imprint material, we made imprints utilizing a 25 mm×25 mm imprint template having reasonably well scattered features (i.e., the features were scattered widely enough to avoid repeated high density patterns—less than 10% of the template surface was covered by features) with feature heights of about 100 nm to provide imprints wherein a typical residual layer thickness was about 50-100 nm (as is well known, solidified polymeric material disposed between features is typically referred to as a residual layer). In particular, we were able to provide void free imprints utilizing the following method steps: (a) pre-cleaning the surface of the imprint template by dipping its surface in a 2.5:1 solution of H₂SO₄and H₂O₂; (b) further pre-treating the surface of the imprint template with a spray of diluted surfactant solution consisting of 0.1% FSO-100 in isopropyl alcohol (“IPA”) where FSO-100 is a surfactant that is available under the designation ZONYL® FSO-100 from DUPONT™ (FSO-100 has a general structure of R₁R₂where R₁=F(CF₂CF₂)_Y, with Y being in a range of 1 to 7, inclusive, and R₂=CH₂CH₂O(CH₂CH₂O)_XH, where X is in a range of 0 to 15, inclusive); (c) purging a gap between the imprint template and the substrate using an ˜5 psi Helium purge; (d) depositing a pattern of substantially equidistant droplets of the following imprinting fluid on the surface of the substrate (where each component is listed by weight): (i) acryloxymethylpentamethyldisiloxane (37 gm) which is available under the designation XG-1064 from Gelest, Inc. of Morrisville, Pa., (ii) isobornyl acrylate (“IBOA”) (42 gm) which is available under the designation SR 506 from Aldrich Chemical Company of Milwaukee, Wis., (iii) ethylene glycol diacrylate (18 gm) which is available under the designation EGDA from Aldrich Chemical Company of Milwaukee, Wis., (iv) a UV photoinitiator, i.e., 2-hydrozy-2-methyl-1-phenyl-propan-1-one (3 gm) which is available under the designation Darocur 1173 from CIBA® of Tarrytown, N.Y.), and (v) FSO-100 (0.5 gm); and (e) performing imprint lithography steps as described above. In this example, the substrate was covered with a transfer layer of a cross-linked BARC material (as is well known, BARC or “bottom antireflective coating” is an organic antireflective coating that is typically produced by a spin-on process). The BARC layer was used to prevent intermixing between the imprinting material and the transfer layer, which intermixing may be particularly problematic when using an imprinting material comprised of low viscosity acrylate components because such components have solvency toward many polymers. Such intermixing may cause problems, such as, for example, and without limitation, distortion of features when the imprint template is separated from the substrate after exposure to polymerizing radiation. In particular, this can be problematic when feature thicknesses are as small as 50 nm to 100 nm.
• Despite the above-described successful imprinting, material voids were observed when we imprinted a high feature density imprint template using the above-described imprinting method. Two important differences between the high feature density imprint template and the above-described imprint template were that the feature density was much higher (for example, and without limitation, about 30% to about 40% of the surface of the template was covered by features in the high feature density imprint template) and the feature height of the high feature density imprint template was much higher, i.e., a height of 200 nm as compared to a height of 100 nm.
• In light of the above, there is a need for imprinting methods and materials for use in imprint lithography that overcome one or more of the above-identified problems.
SUMMARY OF THE INVENTION
• One or more embodiments of the present invention satisfy one or more of the above-identified needs in the art. In particular, one embodiment of the present invention is a method of imprint lithography that comprises depositing an imprinting material on a substrate; varying release properties associated with an imprint template by contacting a solution including imprinting materials and a polymeric fluorinated surfactant; and energizing the imprinting materials to cause a solid material to be produced therefrom. Specifically, it was recognized that employing a polymeric surfactant containing solution to a surface of an imprint template substantially reduced, if not prevented, formation of voids during imprinting. To that end, an exemplary polymeric fluorinated surfactant is 3M™ Novec™ Fluorosurfactant FC-4432. Specifically, it was found that by including in the polymeric fluorinated surfactant in a solution containing imprinting material, the desired release and wetting properties of the imprint template may be established. In this manner, the imprint template may be efficiently wetted with the imprint material, while provided with the desired release properties to reduce, if not prevent, distortions in the pattern recorded in the solidified imprint layer upon separation of the imprint template therefrom. Further, by including the polymeric fluorinated surfactant in the imprinting material is was found the surface energy associated with the imprint template may be regenerated during imprint to maintain the desired release and wetting properties. In accordance with another embodiment, a pre-treatment of the imprint template may be undertaken to coat the imprint template with a polymeric fluorinate surfactant before contacting the imprint material containing solution. In yet another embodiment of the present invention is an imprinting material that includes a polymeric fluorinated surfactant, such as 3M™ Novec™ Fluorosurfactant FC-4432.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a perspective view of a lithographic system useful in carrying out one or more embodiments of the present invention;
• FIG. 2 is a simplified elevation view of a lithographic system shown inFIG. 1;
• FIG. 3 is a simplified representation of material from which an imprinting layer, shown inFIG. 2, is comprised before being polymerized and cross-linked;
• FIG. 4 is a simplified representation of cross-linked polymer material into which the material shown inFIG. 3 is transformed after being subjected to radiation;
• FIG. 5 is a simplified elevation view of a mold spaced-apart from the imprinting layer, shown inFIG. 1, after patterning of the imprinting layer; and
• FIG. 6 is a simplified elevation view of imprint material disposed on a substrate in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
• FIG. 1 showslithographic system10 that may be used to carry out imprint lithography in accordance with one or more embodiments of the present invention and utilizing imprinting materials fabricated in accordance with one or more embodiments of the present invention. As shown inFIG. 1,system10 includes a pair of spaced-apart bridge supports12 havingbridge14 andstage support16 extending therebetween. As further shown inFIG. 1,bridge14 andstage support16 are spaced-apart.Imprint head18 is coupled tobridge14, and extends frombridge14 towardstage support16.Motion stage20 is disposed uponstage support16 to face imprint head, andmotion stage20 is configured to move with respect tostage support16 along X- and Y-axes.Radiation source22 is coupled tosystem10 to impinge actinic radiation uponmotion stage20. As further shown inFIG. 1,radiation source22 is coupled to bridge14, and includespower generator23 connected toradiation source22.
• Referring toFIGS. 1 and 2, connected toimprint head18 isimprint template26 havingmold28 thereon.Mold28 includes a plurality of features defined by a plurality of spaced-apart recessions28aandprotrusions28b. The plurality of features defines an original pattern that is to be transferred intosubstrate31 positioned onmotion stage20.Substrate31 may comprise a bare wafer or a wafer with one or more layers disposed thereon. To that end,imprint head18 is adapted to move along the Z-axis and vary a distance “d” betweenmold28 andsubstrate31. In this manner, features onmold28 may be imprinted into a conformable region ofsubstrate31, discussed more fully below.Radiation source22 is located so thatmold28 is positioned betweenradiation source22 andsubstrate31. As a result,mold28 is fabricated from material that allows it to be substantially transparent to the radiation produced byradiation source22.
• Referring toFIGS. 2 and 3, a conformable region, such asimprinting layer34, is disposed on a portion ofsurface32 that presents a substantially planar profile. It should be understood that the conformable region may be formed using any known technique to produce conformable material onsurface32, such as a hot embossing process disclosed in U.S. Pat. No. 5,772,905 to Chou, which is incorporated by reference in its entirety herein, or a laser assisted direct imprinting (LADI) process of the type described by Chou et al. inUltrafast and Direct Imprint of Nanostructures in Silicon, Nature, Col.417, pp. 835-837, June 2002. In accordance with one embodiment of the present invention, the conformable region consists ofimprinting layer34 being deposited as a plurality of spaced-apartdiscrete droplets36 ofmaterial36aonsubstrate31, discussed more fully below. Imprintinglayer34 is formed from a material36athat may be selectively polymerized and cross-linked to record the original pattern therein, defining a recorded pattern.Material36ais shown inFIG. 4 as being cross-linked atpoints36b, formingcross-linked polymer material36c.
• Referring toFIGS. 2, 3 and5, the pattern recorded inimprinting layer34 is produced, in part, by mechanical contact withmold28. To that end,imprint head18 reduces the distance “d” to allowimprinting layer34 to come into mechanical contact withmold28, spreadingdroplets36 so as to form imprintinglayer34 with a contiguous formation ofmaterial36aoversurface32. In one embodiment, distance “d” is reduced to allow sub-portions34aofimprinting layer34 to ingress into and fillrecessions28a.
• To facilitate filling ofrecessions28a,material36ais provided with the requisite properties to completely fillrecessions28awhile covering surface32 with a contiguous formation ofmaterial36a. In accordance with one embodiment of the present invention, sub-portions34bofimprinting layer34 in superimposition withprotrusions28bremain after the desired, usually minimum distance “d”, has been reached, leaving sub-portions34awith a thickness t₁, and sub-portions34bwith a thickness t₂. Thicknesses “t₁” and “t₂” may be any thickness desired, dependent upon the application.
• Referring toFIGS. 2, 3 and4, after a desired distance “d” has been reached,radiation source22 produces actinic radiation that polymerizes andcross-links material36a, formingpolymer material36cin which a substantial portion thereof is cross-linked. As a result,material36atransforms topolymer material36c, which is a solid, formingimprinting layer134, shown inFIG. 5. Specifically,polymer material36cis solidified to provideside34cofimprinting layer134 with a shape conforming to a shape of asurface28cofmold28, withimprinting layer134 having recesses30 (the bottom of the recesses may be referred to as a residual layer). After imprintinglayer134 is transformed to consist ofpolymer material36c, shown inFIG. 4,imprint head18, shown inFIG. 2, is moved to increase distance “d” so thatmold28 andimprinting layer134 are spaced-apart.
• Referring toFIG. 5, additional processing may be employed to complete the patterning ofsubstrate31. For example,substrate31 andimprinting layer134 may be etched to transfer the pattern ofimprinting layer134 intosubstrate31, providing a patterned surface (not shown). To facilitate etching, the material from whichimprinting layer134 is formed may be varied to define a relative etch rate with respect tosubstrate31, as desired.
• To that end, etching may be performed in a two-step process. S. C. Johnson, T. C. Bailey, M. D. Dickey, B. J. Smith, E. K. Kim, A. T. Jamieson, N. A. Stacey, J. G. Ekerdt, and C. G. Willson describe suitable etch processes in an article entitled “Advances in Step and Flash Imprint Lithography”SPIE Microlithography Conference, February 2003, which article is available on the Internet at www.molecularimprints.com, and which article is incorporated by reference herein. As set forth in the article, the first etch step, referred to as a “break-through etch,” anisotropically removes residualcross-linked material134 to break through to an underlying transfer later (in this respect, better etch selectivity is enabled by keeping the residual layer thin). The second etch step, referred to as a “transfer etch,” uses the remaining pattern incross-linked material134 as an etch mask to transfer the pattern into the underlying transfer layer. In one embodiment, silicon incross-link material134, and lack of silicon in the transfer layer, provides etch selectivity therebetween. In such an embodiment, the etching may be done in a LAM Research 9400SE obtained from Lam Research, Inc. of Fremont, Calif. For example, and without limitation, a halogen “breakthrough etch” may be utilized which comprises an anisotropic halogen reactive ion etch (“RIE”) rich in fluorine, i.e., wherein at least one of the precursors was a fluorine-containing material (for example, and without limitation, a combination of CHF₃and O₂, where the organosilicon nature ofcross-linked material134 may call for the use of a halogen gas). Other suitable halogen compounds include, for example, and without limitation, CF₄. This etch is similar to a standard SiO₂etch performed in modern integrated circuit processing. Next, an anisotropic oxygen reactive ion etch may be used to transfer the features tounderlying substrate31 wherein the remaining silicon containing features serve as an etch mask to transfer the pattern tounderlying substrate31. The “transfer etch” may be achieved, for example, and without limitation, with a standard, anisotropic, oxygen RIE processing tool. However, in general, any suitable etch process may be employed dependent upon the etch rate desired and the underlying constituents that formsubstrate31 andimprinting layer134. Exemplary etch processes may include plasma etching, reactive ion etching, chemical wet etching and the like.
• Referring to bothFIGS. 1 and 2,exemplary radiation source22 may produce ultraviolet radiation; however, any known radiation source may be employed. The selection of radiation employed to initiate the polymerization of the material inimprinting layer34 is known to one skilled in the art and typically depends on the specific application which is desired. Furthermore, the plurality of features onmold28 are shown asrecessions28aextending along a direction parallel toprotrusions28bthat provide a cross-section ofmold28 with a shape of a battlement. However,recessions28aandprotrusions28bmay correspond to virtually any feature required to create an integrated circuit and may be as small as a few tenths of nanometers.
• Referring toFIGS. 1, 2 and5, the pattern produced by the present patterning technique may be transferred intosubstrate31 to provide features having aspect ratios as great as 30:1. To that end, one embodiment ofmold28 hasrecessions28adefining an aspect ratio in a range of 1:1 to 10:1. Specifically,protrusions28bhave a width W₁in a range of about 10 nm to about 5000 μm, andrecessions28ahave a width W₂in a range of 10 nm to about 5000 μm. As a result,mold28 and/ortemplate26, may be formed from various conventional materials, such as, but not limited to, fused-silica, quartz, silicon, organic polymers, siloxane polymers, borosilicate glass, fluorocarbon polymers, metal, hardened sapphire and the like.
• Referring toFIGS. 1, 2 and3, the characteristics ofmaterial36aare important to efficientlypattern substrate31 in light of the deposition process employed. As mentioned above,material36ais deposited onsubstrate31 as a plurality of discrete and spaced-apartdroplets36. The combined volume ofdroplets36 is such that the material36ais distributed appropriately over an area ofsurface32 whereimprinting layer34 is to be formed. As a result,imprinting layer34 is spread and patterned concurrently, with the pattern being subsequently set intoimprinting layer34 by exposure to radiation, such as ultraviolet radiation. As a result of the deposition process, it is desired thatmaterial36ahave certain characteristics to facilitate rapid and even spreading ofmaterial36aindroplets36 oversurface32 so that all thicknesses t₁are substantially uniform and all thicknesses t₂are substantially uniform. The desirable characteristics include having a low viscosity, for example, and without limitation, in a range of about 0.5 to about 10 centepoise (cps), as well as the ability to wet surface ofsubstrate31 andmold28 and to avoid subsequent pit or hole formation after polymerization. Preferably, the viscosity is in a range of 0.5 to 5 cps. With these characteristics satisfied, imprintinglayer34 may be made sufficiently thin while avoiding formation of pits or holes in the thinner regions, such assub-portions34b, shown inFIG. 5.
• The constituent components that form material36ato provide the aforementioned characteristics may differ. This results fromsubstrate31 being formed from a number of different materials. As a result, the chemical composition ofsurface32 varies dependent upon the material from whichsubstrate31 is formed. For example,substrate31 may be formed from silicon, plastics, gallium arsenide, mercury telluride, and composites thereof. Additionally,substrate31 may include one or more layers insub-portion34b, for example, dielectric layer, metal-layer, semiconductor layer, planarization layer and the like.
• Referring toFIGS. 2, 3 and4, it is desired, however, thatmaterial36ainclude components to providemold28 with surface characteristics such thatmold28 may satisfy two—seemingly contradictory—surface energy requirements. Specifically, oncematerial36ais solidified intomaterial36c,mold28 should have the requisite surface energy to release from solidifiedmaterial36cso as to minimize distortions in the pattern recorded in solidifiedmaterial36c. Additionally, to ensure efficient filling of features ofmold28, it is desired that the surface ofmold28 have a sufficiently high surface energy to facilitate wetting ofmold28 withimprinting material36a.
• As was discussed in the Background of the Invention, in accordance with one particular method of imprinting, one manner in which the two aforementioned requirements for mold surface were balanced involved pre-treating the surface ofmold28 and including a surfactant in imprinting material. To that end, a pre-treatment solution including isopropyl alcohol (“IPA”) and a surfactant consisting of 0.1% FSO-100 was employed. The imprinting material also included the surfactant FSO-100. FSO-100 is available under the designation ZONYL® FSO-100 from DUPONT™ and has a general structure of R₁R₂where R₁=F(CF₂CF₂)_Y, with Y being in a range of 1 to 7, inclusive, and R₂=CH₂CH₂O(CH₂CH₂O)_XH, where X is in a range of 0 to 15, inclusive. FSO-100 is a fluorinated surfactant having a molecular weight of about 600, and it aligns efficiently at the surface of the imprint template with hydrophobic —CF₃groups projecting towards the surface of the imprint template. Such alignment is promoted by pre-cleaning the surface (prior to pre-treatment utilizing a surfactant solution consisting of 0.1% FSO-100 in IPA) to create silanol functional groups on the surface. However, the present invention provides an improved method and material that substantially reduces, if not prevents, void formation when imprinting high density features having a height of about 200 nm.
• This is achieved, in part, by employing a polymeric fluorinated surfactant. An exemplary polymeric fluorinated surfactant is available under the designation 3M™ Novec™ Fluorosurfactant FC-4432 (hereafter referred to as FC-4432) from 3M Company of St. Paul, Minn. in the manner described in detail below to provide an imprinting material and methods for imprint lithography. FC-4432 is a non-ionic polymeric fluorochemical surfactant belonging to a class of coating additives which provide low surface tensions in organic coating systems. The composition of FC-4432 is 87% polymeric fluorochemical actives, 7% non-fluorochemical actives, 5% 1-methyl-2-pyrudiinone, and <1% toluene. FC-4432 is a wetting, leveling and flow control agent for radiation curable polymer coating systems, and continues to be active throughout the curing process. FC-4432 is the first in a new line of fluorochemical surfactants from the 3M Company based on perfluorosulfate (PFBS), where PFBS refers collectively to perfluorobutane sulfonyl compounds including perfluorobutance sulfonates. In addition, such PFBS-based surfactants with only four perfluorinated carbon atoms offer improved environmental properties. The molecular weight of FC-4432 is about 4000, and because of its higher molecular weight than that of FSO-100, the fluorinated groups of FC-4432 align differently at the surface of an imprint template than those in FSO-100. In particular, besides —CF₃groups of FSO-100, FC-4432 has a higher percentage of —CF₂groups situated at the surface when compared to FSO-100. Because a —CF₂group provides a higher surface energy than a —CF₃group, the presence of a higher percentage of —CF₂groups in FC-4432 at template surface provides a material having better wetting than FS-100. However, despite its higher surface energy, a —CF2— group is hydrophobic enough so that its use produces a material having a good release property. In addition, it is believed that the higher molecular weight of FC-4432 (when compared to that of FSO-100) causes FC-4432 to act like a loosely packed coil structure that results in more porous molecular packing of surfactant molecules at the surface of the imprint template. It is further believed that this coil structure helps enhance wetting over that provided by FSO-100, and in addition to that provided by the presence of a higher percentage of surface —CF₂groups in FC-4432 when compared to FSO-100.
• An exemplary composition formaterial36athat utilizes the surfactant FC-4432 is produced by mixing (with exemplary proportions being given in weight): (i) acryloxymethylpentamethyldisiloxane (for example, and without limitation, about 37 gm) which is available under the designation XG-1064 from Gelest, Inc. of Morrisville, Pa., (ii) isobornyl acrylate (“IBOA”) (for example, and without limitation, about 42 gm) which is available under the designation SR 506 from Aldrich Chemical Company of Milwaukee, Wis., (iii) ethylene glycol diacrylate (for example, and without limitation, about 18 gm) which is available under the designation EGDA from Aldrich Chemical Company of Milwaukee, Wis., (iv) a UV photoinitiator, for example, and without limitation, 2-hydrozy-2-methyl-1-phenyl-propan-1-one (for example, and without limitation, about 3 gm) which is available under the designation Darocur 1173 from CIBA® of Tarrytown, N.Y.), and (v) FC-4432 (for example, and without limitation, about 0.5 gm). The above-identified composition may also include stabilizers that are well known in the chemical art to increase the operational life of the composition. In a typical such embodiment, the surfactant comprises less than 1% of the imprinting material. However, the percentage of the surfactant may be greater than 1%.
• An advantage provided by the above-described imprinting material is that it abrogates the need for an a priori release layer, i.e., a separate hydrophobic and/or low surface energy release layer disposed on imprint template28 (as described in the Background of the Invention). Specifically, the imprinting material provides desirable release properties to mold28 andimprinting layer34 so thatmaterial36c, shown inFIG. 4, does not adhere to mold28 with sufficient force to distort the pattern recorded therein.
• Referring toFIG. 6, it is believed that surfactant molecules indroplets36 of the imprinting material preferentially move toward the gas-liquid interface in less than about 1 sec. As such, it is believed thatdroplets36 have a higher concentration of the surfactant inregion136 when compared withregion137 in which the polymerizable components are concentrated. It is believed that this is the result of an energy minimization process wherein the surfactant tends to move to the gas-liquid interface so that its hydrophobic end aligns towards the gas. For example, it is believed that the fluorinated, hydrophobic end of the FC-4432 (for example, comprised of —CF₃and —CF₂groups) is aligned to project out of the liquid and into the gas, and the hydrophilic end (i.e., —OH and polar ethylene oxide groups) is aligned to project into the liquid. However, when the imprinting material contacts the surface of the imprint template, it is believed that exposed silanol bonds on the surface of the imprint template cause the hydrophilic end of the surfactant molecule to flip and to contact the exposed silanol bonds so that —CF3 groups and —CF₂groups face downward (i.e., outward from the surface of the imprint template) to enable adhesion reduction. It is further believed that surfactant lamella may also be formed at the surface of the imprint template, which lamella may comprise, for example, two (2) layers of surfactant molecules.
• Referring toFIG. 2, an additional advantage provided by the above-described imprinting material is that the time required to wetmold28 and, therefore, to spreaddroplets36 may be reduced. Specifically, by abrogating the need to have an a priori release layer onmold28, the surface ofmold28 may be provided with increased surface energy. Of course, the above-described imprinting material may be employed with an a priori release layer, such as those known in the prior art.
• Another manner by which to improve the release properties ofmold28 includes conditioning the pattern ofmold28 by exposing the same to a conditioning mixture including an additive that will remain onmold28 to reduce the surface energy of the mold surface. An exemplary additive is a surfactant.
• The above-described imprinting material is useful in providing substantially void free imprint lithography utilizing high feature density and relatively tall feature height (for example, and without limitation, feature heights of about 200 nm) with residual layer thicknesses of 50-100 nm (note that providing thin residual layers requires low viscosity and small drops of imprinting material, i.e., viscosity below about 10 cps, and preferably below 5 cps, and drops at or below about 80 pico-liters).
• The following describes a method for imprint lithography that utilizes one or more embodiments of the above-described imprinting material. As a first step, the surface of a quartz imprint template is pre-treated to create hydrophilic bonds at the surface, for example, and without limitation silanol (Si—OH) bonds. In accordance with one or more embodiments of the present invention, the surface of the imprint template is dipped in a 2.5:1 solution of H₂SO₄and H₂O₂to hydrolyze the surface, i.e., to create silanol bonds at the surface. As a next step, the surface is further pre-treated by spraying the surface of the imprint template with a diluted FC-4432 solution (for example, and without limitation, 0.1% FC-4432 in IPA). Exposure of the surface of the imprint template may be achieved by virtually any method known in the art, including dipping the surface into a volume of pre-treatment solution, wiping the surface with a cloth saturated with pre-treatment solution, and spraying a stream of pre-treatment solution onto the surface. The IPA in the pre-treatment solution may be allowed to evaporate before using themold28. In this manner, the IPA facilitates removing undesired contaminants from the surface while leaving the surfactant. Because the surfactant includes a hydrophobic, fluorine-rich end, and a hydrophilic end, the silanol groups promote alignment of the surfactant so that the hydrophilic end “adsorbs” to the —OH end of the silanol groups, and the hydrophobic, fluorine-rich end points away from the surface. In a next step, a gap between the imprint template and the substrate may be purged of air (mainly O₂and N₂) using, for example, and without limitation, an ˜5 psi Helium purge. In a next step, the imprinting material containing the FC-4432 surfactant is applied to the substrate, for example, and without limitation, by placing a pattern of substantially equidistant droplets of imprinting material on the substrate, by spin-coating, or by any other method known to those of ordinary skill in the art. In this example, the substrate was covered with a transfer layer whose top layer was a cross-linked BARC material (BARC or “bottom antireflective coating” is an organic antireflective coating that is typically produced by a spin-on process). The BARC layer was used to prevent intermixing between an imprinting material and the transfer layer, which intermixing may be particularly problematic when using an imprinting material comprised of low viscosity acrylate components because such components have solvency toward many polymers. Intermixing may cause problems such as, for example, and without limitation, distortion of features when an imprint template is separated from a substrate after exposure to polymerizing radiation. This can be particularly problematic when feature thicknesses are as small as 50 to 100 nm. Next, the familiar steps of imprint lithography are carried out, i.e., exposure to actinic radiation to polymerize the imprinting material; separation of the imprint template and the substrate; and selective etching to transfer the feature pattern to the substrate.
• It is believed that the use of surface pre-treatments described above utilizing FC-4432 may be useful by itself in helping to provide substantially void free imprint lithography. For example, we have run experiments where the surface was pre-treated as described directly above, and wherein the imprinting material included FSO-100 as a surfactant rather than FC-4432. In this case a few void free imprints were made, but it is believed that as soon as the FC-4432 supplied to the surface of the imprint template by pre-treatment was abraded away, imprints having voids soon appeared.
• It is believed that even when pre-treating the surface of the imprint template as described above utilizing FC-4432, FC-4432 adhered to the silanol groups on the surface of the imprint template ultimately is abraded away. However, as was described above, the FC-4432 contained in the imprinting material itself rapidly comes to the gas-liquid surface of the droplets, and the surface of the imprint template is re-coated with FC-4432 as a normal consequence of imprinting. As such, in accordance with one or more embodiments of the present invention, the pre-treatment step of applying the surfactant solution to the surface of the imprint template may be eliminated. In fact, in accordance with one or more further embodiments of the present invention, the imprint template may be contacted a few times with the imprinting material as a replacement for the pre-treatment step of applying the surfactant solution to the surface. In this manner, the use of the polymeric fluorinated surfactant, as discussed above, enables varying the surface characteristics ofmold28, and thereforetemplate26, to satisfying the two aforementioned contradictory surface energy requirements.
• 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. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.

Claims (21)

1. A method of imprint lithography that comprises:

depositing an imprinting material on a substrate;

varying release properties associated with an imprint template by contacting a solution including imprinting materials and a polymeric fluorinated surfactant; and

energizing the imprinting materials to cause a solid material to be produced therefrom.

2. The method as recited inclaim 1 wherein said varying further include providing said solution with a mixture of said imprinting materials and 3M™ Novec™ Fluorosurfactant FC-4432.

3. The method ofclaim 1 which includes pre-treating the surface of the imprint template to be hydrophilic.

4. The method ofclaim 2 which includes further pre-treating the surface of the imprint template by applying a composition that includes the surfactant.

5. The method ofclaim 4 wherein the composition is a mixture of isopropyl alcohol and the surfactant.

6. A method of imprint lithography that comprises:

depositing an imprinting material on a substrate;

moving an imprint template towards the substrate so that the imprinting materials coats a surface of the imprint template and a surface of the substrate; and

energizing the imprinting material to cause a solid material to be produced therefrom; and

wherein the imprinting material includes a surfactant having a composition that includes 87% polymeric fluorochemical actives, 7% non-fluorochemical actives, 5% 1-methyl-2-pyrudiinone, and <1% toluene.

7. The method ofclaim 1 wherein the imprinting material includes acryloxymethylpentamethyldisiloxane, isobornyl acrylate, ethylene glycol diacrylate, and 2-hydrozy-2-methyl-1-phenyl-propan-1-one.

8. The method ofclaim 6 wherein the imprinting material includes acryloxymethylpentamethyldisiloxane, isobornyl acrylate, ethylene glycol diacrylate, and 2-hydrozy-2-methyl-1-phenyl-propan-1-one.

9. The method ofclaim 7 wherein the surfactant is <1% of the imprinting material.

10. The method ofclaim 8 wherein the surfactant is <1% of the imprinting material.

11. The method ofclaim 6 wherein depositing includes depositing a plurality of droplets upon the substrate.

12. The method ofclaim 6 wherein depositing includes spin-coating.

13. The method ofclaim 6 which includes pre-treating the surface of the imprint template to be hydrophilic.

14. The method ofclaim 13 wherein pre-treating includes hydrolyzing.

15. The method ofclaim 14 wherein hydrolyzing includes forming —OH bonds at the surface of the imprint template.

16. A method of imprint lithography that comprises:

pre-treating a surface of an imprint template to cause it to be hydrophilic;

pre-treating the surface of the imprint template by applying a composition that includes 3M™ Novec™ Fluorosurfactant FC-4432;

depositing an imprinting material on a substrate;

moving an imprint template towards the substrate so that the imprinting materials coats the surface of the imprint template and a surface of the substrate; and

energizing the imprinting material to cause a solid material to be produced therefrom.

17. An imprinting material for use in imprint lithography that comprises a polymeric fluorinated surfactant.

18. The imprinting material ofclaim 17 wherein said polymeric fluorinated surfactant consists of 3M™ Novec™ Fluorosurfactant FC-4432.

19. The imprinting material ofclaim 17 which further includes a UV photoinitiator.

20. The imprinting material ofclaim 19 which further includes acryloxymethylpentamethyldisiloxane, isobornyl acrylate, ethylene glycol diacrylate, and 2-hydrozy-2-methyl-1-phenyl-propan-1-one.

21. The imprinting material ofclaim 18 wherein 3M™ Novec™ Fluorosurfactant FC-4432 comprises <1% of the material.

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