Abstract:
One embodiment of the present invention is a method for generating patterned features on a substrate that includes: (a) forming a first layer on at least a portion of a surface of the substrate, the first layer comprising at least one layer of a first material, which one layer abuts the surface of the substrate; (b) forming a second layer of a second material on at least a portion of the first layer, which second layer is imprinted with the patterned features; (c) removing at least portions of the second layer to extend the patterned features to the first layer; and (d) removing at least portions of the first layer to extend the patterned features to the substrate; wherein the first layer and the second layer may be exposed to an etching process that undercuts the patterned features, and the first material may be lifted-off.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     One or more embodiments of the present invention relate generally to methods for fabricating patterned features utilizing imprint lithography.  
         [0002]     There is currently a strong trend, for example and without limitation, in the semiconductor manufacturing industry, toward micro-fabrication, i.e., fabricating small structures and downsizing existing structures. For example, micro-fabrication typically involves fabricating structures having features on the order of micro-meters or smaller.  
         [0003]     One area in which micro-fabrication has had a sizeable impact is in microelectronics. In particular, downsizing microelectronic structures has generally enabled such microelectronic structures to be less expensive, have higher performance, exhibit reduced power consumption, and contain more components for a given dimension relative to conventional electronic devices. Although micro-fabrication has been utilized widely in the electronics industry, it has also been utilized in other applications such as biotechnology, optics, mechanical systems, sensing devices, and reactors.  
         [0004]     As is well known, methods for fabricating patterned features are an important part of micro-fabrication. In the art of micro-fabrication of, for example and without limitation, semiconductor devices, “lift-off” is a well known method for fabricating patterned metal features such as, for example and without limitation, lines on a substrate or wafer.  FIGS. 1A-1D  illustrate a well known process for fabricating patterned metal features in which a photoresist mask is undercut by a developer prior to metal deposition. As shown in  FIG. 1A , substrate  100  has been coated with photoresist layer  110  in accordance with any one of a number of methods that are well known to those of ordinary skill in the art, and photoresist mask layer  110  has been patterned in accordance with any one of a number of methods that are well known to those of ordinary skill in the art to provide aperture  120  having relatively straight side walls. For example, in accordance with one such lithography technique, photoresist  110  was exposed to a beam of electrons, photons, or ions by either passing a flood beam through a mask or scanning a focused beam. The beam changed the chemical structure of an exposed area of photoresist layer  110  so that, when immersed in a developer, either the exposed area or an unexposed area of photoresist layer  110  (depending on the type of photoresist used) was removed to recreate a pattern, or its obverse, of the mask or the scanning. Next, as shown in  FIG. 1B , aperture  120  has been undercut in accordance with any one of a number of methods that are well known to those of ordinary skill in the art to form aperture  130  in photoresist mask layer  110 . Next, as shown in  FIG. 1C , a relatively thin metal layer has been blanket-deposited over the structure shown in  FIG. 1B . As is well known, metal thin film deposition techniques such as, for example and without limitation, physical vapor deposition (“PVD”) or sputtering (and excepting conformal deposition techniques such as, for example and without limitation, chemical vapor deposition (“CVD”) and electroplating) provide limited step coverage. As a result, metal deposited using such techniques does not coat steep or undercut steps. Thus, as shown in  FIG. 1C , after blank metal deposition, the undercut side walls of aperture  130  are not coated. In other words, the use of undercut aperture  130  in photoresist mask layer  110  avoids side wall metal deposition, and provides discontinuous metal regions on substrate  100  and photoresist mask layer  110 . Lastly, as shown in  FIG. 1D , a photoresist lift-off process has been carried out in accordance with any one of a number of methods that are well known to those of ordinary skill in the art to provide patterned metal feature  150  on substrate  100 . As is well known, during the lift-off process, photoresist material under metal film  140  is removed using, for example and without limitation, a solvent or a photoresist stripper. As a result, metal film  140  is removed, and patterned metal feature  150  that was deposited directly on substrate  100  remains.  
         [0005]     Lithography is an important technique or process in micro-fabrication that is used to fabricate semiconductor integrated electrical circuits, integrated optical, magnetic, mechanical circuits and microdevices, and the like. As is well known, and as was discussed above, lithography may be used to create a pattern in a thin film carried on a substrate or wafer so that, in subsequent processing steps, the pattern can be replicated in the substrate or in another material that is deposited on the substrate. An imprint lithography technology for producing nanostructures with 10 nm feature sizes has been discussed in the literature. One embodiment of imprint lithography—referred to in the art as Step and Flash Imprint Lithography (“SFIL”)—is disclosed in an article by B. J. Smith, N. A. Stacey, J. P. Donnelly, D. M. Onsongo, T. C. Bailey, C. J. Mackay, D. J. Resnick, W. J. Dauksher, D. Mancini, K. J. Nordquist, S. V. Sreenivasan, S. K. Banerjee, J. G. Ekerdt, and C. G. Willson entitled “Employing Step and Flash Imprint Lithography for Gate Level Patterning of a MOSFET Device”  SPIE Microlithography Conference, February  2003, which article is available on the Internet at www.molecularimprints.com, and which article is incorporated by reference herein. SFIL is a lithography technique that enables patterning of sub-100 nm features at a cost that has the potential to be substantially lower than either conventional projection lithography or proposed next generation lithography techniques. As described in the article, SFIL is a molding process that transfers the topography of a rigid transparent template using a low-viscosity, UV-curable organosilicon solution at room temperature with low pressure mechanical processes.  
         [0006]     One such SFIL process is illustrated in conjunction with  FIGS. 2A-2F . As shown in  FIG. 2A , thinorganic layer  210  (referred to as a transfer layer) has been spin-coated on silicon substrate  200 . Next, a small amount of low viscosity, photopolymerizable, organosilicon solution  220  is dispensed over transfer layer  210  in an area to be imprinted (solution  220  is sometimes referred to as an “imprinting material”). The viscosity of solution  220  is sufficiently low so that minimal pressure (for example and without limitation, a pressure of about 2-4 psi) and no additional heating is necessary to move the liquid into an imprint template. For example, solution  220  may be a solution of an organic monomer, a silylated monomer, and a dimethyl siloxane oligomer (“DMS”) and a multifunctional cross-linker. Each component plays a role in the imaging process. For example: (a) the free radical generator initiates polymerization upon exposure to actinic (typically UV) radiation; (b) the organic monomer ensures adequate solubility of the free radical generator, desirable cohesive strength of cured imprinting material and adhesion to underlying organic transfer layer  210 ; (c) and the silylated monomers and the DMS provide silicon required to provide high-oxygen etch resistance (useful in subsequent processing steps described below); and (d) multi-functional crosslinker provides chemical crosslinking. In addition, these monomer types help maintain a low viscosity that is useful during imprinting. In further addition, the silylated monomer and the DMS derivative also lower the surface energy of solution  220 , thereby enhancing a separation process (described below). Advantageously, the organic monomer polymerizes in a fraction of a second using low cost, broadband light sources. For example, as described in the article, solution  220  consisted of 15% (w/w) ethylene glycol diacrylate (obtained from Aldrich Chemical Company of Milwaukee, Wis.), 44% (3-acryloxypropyl)tris(trimethylsiloxy)silane (obtained under the trade name SIA0210.0 from Gelest, Inc. of Morrisville, Pa.), 37% t-butyl acrylate (obtained from Lancaster Synthesis Inc. of Windham, N.H.), and 4% 2-hydrozy-2-methyl-1-phenyl-propan-1-one (obtained under the trade name Darocur 1173 from CIBA® of Tarrytown, N.Y.).  
         [0007]     Next, as shown in  FIG. 2B , template  230 —bearing patterned relief structures (for example and without limitation, a circuit pattern) and whose surface was treated with a fluorocarbon release film—was aligned over dispensed solution  220  and moved to decrease a gap between template  230  and substrate  200 . This displaced solution  220 , and filled the patterned relief structures on template  230 . Suitable release layers are described in an article by D. J. Resnick, D. P. Mancini, S. V. Sreenivasan, and C. G. Willson entitled “Release Layers for Contact and Imprint Lithography”  Semiconductor International , June 2002, pp. 71-80, which article is incorporated by reference herein. As is known, it is desired that a template release layer has a low enough surface energy to enable template/substrate separation, and also is reasonably durably bonded to the template surface to remain functional after a number of imprints. Alkyltrichlorosilanes form strong covalent bonds with a surface of fused silica, or SiO 2 . In addition, in the presence of surface water, they react to form silanol intermediates which undergo a condensation reaction with surface hydroxyl groups and adjacent silanols to form a networked siloxane monolayer. When this functional group is synthetically attached to a long fluorinated aliphatic chain, a bifunctional molecule suitable as a template release film may be created. The silane-terminated end bonds itself to a template&#39;s surface, providing durability useful for repeated imprints. The fluorinated chain, with its tendency to orient itself away from the surface, forms a tightly packed comb-like structure, and provides a low-energy release surface. Annealing further enhances the condensation, thereby creating a highly networked, durable, low surface energy coating.  
         [0008]     Next, as shown in  FIG. 2C , once filling has occurred, the area is irradiated with broadband UV ultraviolet light (for example and without limitation, a 500 W Hg arc lamp) through a back side of template  230 , and cross-linking of solution  220  occurs.  
         [0009]     Next, as shown in  FIG. 2D , template  230  and substrate  200  are mechanically separated to expose cured, organosilicon relief pattern  240  (an imprinted version of the relief pattern in template  230 ) that is disposed on residual layer  250  (a residue of cross-linked solution  220 ). The SFIL steps illustrated in  FIGS. 2A-2D  may be carried out in a tool described by I. McMackin, P. Schumaker, D. Babbs, J. Choi, W. Collison, S. V. Sreenivasan, N. Schumaker, M. Watts, and R. Voisin in an article entitled “Design and Performance of a Step and Repeat Imprinting Machine”  SPIE Microlithography Conference , February 2003, which article is available on the Internet at www.molecularimprints.com, and which article is incorporated by reference herein.  
         [0010]     Next, etching is 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 residual cross-linked layer  250  to break through to underlying transfer later  210 . The second etch step, referred to as a “transfer etch,” uses the remaining cross-linked relief pattern  240  as an etch mask to transfer the pattern into underlying transfer layer  210 . In one embodiment of SFIL, silicon in polymerized solution  220 , and lack of silicon in transfer layer  210 , provides etch selectivity between polymerized solution  220  and transfer layer  210 . In such an embodiment, the etching may be done in a LAM Research 9400SE obtained from Lam Research, Inc. of Fremont, Calif.  
         [0011]     As shown in  FIG. 2E , a halogen “breakthrough etch” was performed. For example and without limitation, the halogen etch described in the article was 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 CHF 3  and O 2 , where the organosilicon nature of solution  220  called for the use of a halogen gas). Other suitable halogen compounds include, for example and without limitation, CF 4 . This etch is similar to a standard SiO 2  etch performed in modern integrated circuit processing. Lastly, as shown in  FIG. 2F , an anisotropic oxygen reactive ion etch was used to transfer features  260  to underlying substrate  200 . The remaining silicon containing features  260  served as an etch mask to transfer the pattern to underlying substrate  200 . The “transfer etch” was achieved with a standard, anisotropic, oxygen RIE processing tool.  
         [0012]     In order to imprint sub-100 nm features, it is useful to avoid intermixing between an imprinting material and a transfer layer. 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. In addition, intermixing may be particularly problematic when using an imprinting material comprised of low viscosity acrylate components because such components have solvency toward many polymers. Because of this, some have used a cross-linked BARC material (BARC or “bottom antireflective coating” is an organic antireflective coating that is typically produced by a spin-on process) as a transfer layer. However, because BARC is cross-linked, it cannot be undercut by conventional wet developers and removed by organic photostrippers. As a result, the above described method for fabricating patterned metal features using lift-off cannot be used.  
         [0013]     In light of the above, there is a need for methods for fabricating patterned features utilizing imprint lithography that overcome one or more of the above-identified problems.  
       SUMMARY OF THE INVENTION  
       [0014]     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 for generating patterned features on a substrate that includes: (a) forming a first layer on at least a portion of a surface of the substrate, the first layer comprising at least one layer of a first material, which one layer abuts the surface of the substrate; (b) forming a second layer of a second material on at least a portion of the first layer, which second layer is imprinted with the patterned features; (c) removing at least portions of the second layer to extend the patterned features to the first layer; and (d) removing at least portions of the first layer to extend the patterned features to the substrate; wherein the first layer and the second layer may be exposed to an etching process that undercuts the patterned features, and the first material may be lifted-off.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIGS. 1A-1D  illustrate a well known process for fabricating patterned metal features in which a photoresist mask is undercut by a developer prior to metal deposition;  
         [0016]      FIGS. 2A-2F  illustrate a step-by-step sequence for carrying out one example of one type of imprint lithography process, a Step and Flash Imprint Lithography (“SFIL”) process;  
         [0017]      FIGS. 3A-3I  illustrate a step-by-step sequence for fabricating patterned features in accordance with one or more embodiments of the present invention utilizing imprint lithography;  
         [0018]      FIG. 4  shows a portion of a structure of a chemical used to fabricate a planarization and transfer layer in accordance with one or more embodiments of the present invention; and  
         [0019]      FIG. 5  illustrates an alternative step for that illustrated in  FIG. 3B . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]      FIGS. 3A-3I  illustrate a step-by-step sequence for fabricating patterned features in accordance with one or more embodiments of the present invention utilizing imprint lithography. Imprint lithography steps may be carried using a tool described by I. McMackin et al. in an article entitled “Design and Performance of a Step and Repeat Imprinting Machine”  SPIE Microlithography Conference , February 2003, which article is cited in the Background of the Invention, and which article is incorporated by reference herein.  
         [0021]     As shown in  FIG. 3A , planarization and transfer layer  310  has been formed on substrate or wafer  300  using any one of a number of methods that are well known to those of ordinary skill in the art such as, for example and without limitation, by spin-coating to provide a substantially continuous, planar surface over substrate  300 . In accordance with one or more embodiments of the present invention, an inventive planarization and transfer layer is a polymer containing a poly(dimethylglutarimide) (“PMGI”) structure.  FIG. 4  shows the structure of PMGI used to form the polymer of inventive planarization and transfer layer. Advantageously, in accordance with one or more embodiments of the present invention, a planarization and transfer layer based on PMGI has the following beneficial properties that solve one or more of the problems identified in the Background of the Invention: (a) little, if any, interfacial mixing with acrylic-based imprinting fluids; (b) such a planarization and transfer layer is removable in developer(s)/stripper(s), for example and without limitation, wet developer(s)/stripper(s) (it is believed that this is because such a planarization and transfer layer is not cross-linked by exposure to the UV radiation used to polymerize the imprinting fluid); and (c) such a planarization and transfer layer does not cross-link in response to UV radiation.  
         [0022]     A polymer containing a PMGI structure that is suitable for use in carrying out one or more embodiments of the present invention may be obtained under the trade name SF7S (“PMGI SF7S”) from MicroChem Corp. of Newton, Mass. Other polymers containing a PMGI structure that are also suitable for use in carrying out one or more embodiments of the present invention may be obtained under the trade names LOL1000 and LOL2000 from Shipley Company, L.L.C. of Marlborough, Mass. In accordance with one embodiment of the present invention, PMGI SF7S was spin coated on a silicon wafer at about 3,000 rpm (conventional spin-coaters may rotate at speeds from about 500 to about 6000 rpm). The wafer was soft baked at about 180° C. for about 5 min, and a thickness of the PMGI layer was about 500 nm. Advantageously further embodiments of the present invention may be fabricated readily by one of ordinary skill in the art without undue experimentation since the developmental characteristics of a polymer containing a PMGI structure may be controlled by bake time and bake temperature.  
         [0023]     As further indicated in  FIG. 3A , feature pattern  325  has been fabricated on imprint template  330  using any one of a number of methods that are well known to those of ordinary skill in the art. In accordance with one or more embodiments of this imprint lithography process, imprint template  330  may have a nanoscale relief structure formed therein having an aspect ratio ranging, for example and without limitation, from about 1×10 −5  to about 10. Specifically, the relief structures in imprint template  330  may have a width that ranges, for example and without limitation, from about 10 nm to about 5000 μm, and the relief structures may be separated from each other by a distance that ranges, for example and without limitation, from about 10 nm to about 5000 μm. In accordance with one or more embodiments of the present invention, imprint template  330  may be comprised of material that is transparent, at least to a desired extent, to radiation utilized to cross-link an imprint fluid. Such material may be, for example and without limitation, SiO 2 , in the form of quartz, fused-silica, sapphire and the like.  
         [0024]     In accordance with one or more embodiments of the present invention, a surface of imprint template  330  may be treated with a surface modifying agent such as a fluorocarbon silylating agent to promote release of imprint template  330  after transfer of feature pattern  325 . In addition, in accordance with one or more embodiments of this imprint lithography process, the step of treating the surface of imprint template  330  may be carried out utilizing a technique such as, for example and without limitation, a plasma technique, a chemical vapor deposition technique, a solution treatment technique, and combinations thereof. In accordance with one or more further embodiments of the present invention, the release properties of imprint template  330  may be improved by conditioning feature pattern  325  of imprint template  330  by exposing it to a conditioning mixture including an additive that will remain on imprint template  330  to reduce the surface energy of its surface. An exemplary additive is a surfactant such as, for example and without limitation, a mixture that includes approximately 0.1% or more of a surfactant available under the trade name ZONYL® FSO-100 from DUPONT™ having a general structure of R 1 R 2  where R 1 ═F(CF 2 CF   2 ) Y , with y being in a range of 1 to 7, inclusive and R 2 ═CH 2 CH   2 O(CH 2 CH 2 O) X H, where X is in a range of 0 to 15, inclusive—with the remainder comprising isopropyl alcohol (“IPA”) Exposure of feature pattern  325  may be achieved by virtually any manner known in the art, including dipping feature pattern  325  into a volume of the conditioning mixture, wiping the pattern with a cloth saturated with the conditioning mixture and spraying a stream of the conditioning mixture onto the surface. The IPA in the conditioning mixture is allowed to evaporate before using imprint template  330 . In this manner, the IPA facilitates removing, from the pattern, undesired contaminants while leaving the additive, thereby conditioning the surface of the pattern. In accordance with one or more still further embodiments of the present invention, the feature pattern of imprint template  330  may be conditioned by pattern priming. Pattern priming is achieved by selectively contacting the imprint fluid (to be described below) with the pattern a sufficient number of times to accurately reproduce a pattern complementary to the initial pattern. Specifically, by repeatedly contacting the imprint fluid, the complementary pattern formed improves with each successive imprint. After a sufficient number of imprints, an accurate complementary reproduction of the pattern in imprint template  330  is formed.  
         [0025]     In addition, in accordance with one or more embodiments of the present invention, and has been indicated in  FIG. 3A , release layer  320  has been deposited on imprint template  330 . An important factor in accurately forming feature pattern  325  is to reduce, if not prevent, adhesion of polymerized imprint fluid to imprint template  330 ′. A release layer is typically hydrophobic and/or has low surface energy. Providing polymerized imprint fluid with improved release characteristics minimizes distortions in feature pattern  325  recorded into the polymerized imprint fluid upon template separation. This type of release layer may be referred to as an a priori release layer, i.e., a release layer that is solidified to the mold. Suitable release layers are described in an article by D. J. Resnick, D. P. Mancini, S. V. Sreenivasan, and C. G. Willson entitled “Release Layers for Contact and Imprint Lithography”  Semiconductor International , June 2002, pp. 71-80, which article is cited in the Background of the Invention, and which article is incorporated by reference herein.  
         [0026]     As further indicated in  FIG. 3A , imprint template  330  is aligned over and spaced apart from planarization and transfer layer  310 .  
         [0027]     Next, as shown in  FIG. 3B , polymerizable fluid  340  (also referred to as an “imprint fluid” or “imprint material”) has been dispensed over planarization and transfer layer  310  using any one of a number of methods that are well known to those of ordinary skill in the art such as, for example and without limitation, by dispensing as a plurality of fluid beads or droplets. As further shown in  FIG. 3B , imprint template  330  has been brought close enough to polymerizable fluid  340  so that the features in feature pattern  325  of imprint template  330  have been filled with polymerizable fluid  340 . Note that polymerizable fluid  340  has a viscosity sufficiently low that it may rapidly and evenly spread and fill the features in an efficient manner, for example and without limitation, a viscosity in a range from about 0.01 cps to about 100 cps measured at 25° C. In addition, polymerizable fluid  340  has an ability to wet the surface of planarization and transfer layer  310  and imprint template  330 , and to avoid subsequent pit or hole formation after polymerization.  
         [0028]     The constituent components that form polymerizable fluid  340  to provide the aforementioned characteristics may differ. This results from substrate  300  being formed from a number of different materials. As a result, the chemical composition of planarization and transfer layer  310  varies dependent upon the material from which substrate  300  is formed. For example, and without limitation, substrate  300  may be formed from silicon, plastics, gallium arsenide, mercury telluride, and composites thereof. Additionally, substrate  300  may include one or more layers, for example and without limitation, dielectric layers, metal layers, semiconductor layers, and the like.  
         [0029]     In accordance with one or more such embodiments of the present invention, polymerizable fluid  340  comprises further constituents that provide its low viscosity, selectable etchability with respect to planarization and transfer layer  310  (to be described in detail below). In accordance with one or more such embodiments of the present invention, polymerizable fluid  340  is comprised of a silicon-containing material such as, for example and without limitation, an organosilane.  
         [0030]     An exemplary composition for the silicon-containing material includes: (a) isobornyl acrylate (obtained from Aldrich Chemical Company of Milwaukee, Wis.); (b) acryloxymethyltrimethylsilane (obtained under the trade name XG-1039 from Gelest, Inc. of Morrisville, Pa.); (c) (3-acryloxypropyltristrimethylsiloxy)silane (obtained under the trade name SIA0210.0 from Gelest, Inc. of Morrisville, Pa.); (d) a fluorinated surfactant (obtained under the trade name FC4432 from 3M Company St. Paul, Minn.); (e) ethylene glycol diacrylate (obtained under the trade name EGDA from Aldrich Chemical Company of Milwaukee, Wis.); and (f) UV photoinitiator (for example and without limitation, 2-hydroxy-2-methyl-1-phenyl-propan-1-one) (obtained under the trade name Darocur  1173  from CIBA® of Tarrytown, N.Y.). In an exemplary such composition, isobornyl acrylate comprises approximately 30% by weight of the composition, acryloxymethyltrimethylsilane comprises approximately 40% by weight of the composition, (3-acryloxypropyltristrimethylsiloxy)silane comprises approximately 10% by weight of the composition, the fluorinated surfactant comprises approximately 0.5% by weight of the composition, ethylene glycol diacrylate comprises approximately 20% by weight of the composition, and the UV photoinitiator comprises approximately 3% by weight of the composition. Further useful compositions using the above-described materials may be determined readily by one of ordinary skill in the art without undue experimentation. Advantageously, little or no interfacial mixing occurs between polymerizable fluid  340  and planarization and transfer layer  310  for these above-described embodiments.  
         [0031]     In accordance with one or more alternative embodiments of the present invention, polymerizable fluid  340  may comprise a nonsilicon-containing material such as, for example and without limitation, (a) isobornyl acrylate; (b) n-hexyl acrylate; (c) ethylene glycol diacrylate; and (d) 2-hydroxy-2-methyl-1-phenyl-propan-1-one. In one such exemplary composition, isobornyl acrylate comprises approximately 55% of the composition, n-hexyl acrylate comprises approximately 27% of the composition, ethylene glycol diacrylate comprises approximately 15% of the composition, and the UV initiator, for example and without limitation, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, comprises approximately 3% of the composition. The above-identified composition may also include stabilizers that are well known in the chemical art to increase the operational life of the composition. Further useful compositions using the above-described materials may be determined readily by one of ordinary skill in the art without undue experimentation.  
         [0032]     To improve the release properties of imprint template  330  and polymerized layer  345  and to ensure that polymerized layer  345  does not adhere to imprint template  330 , the composition from which polymerizable fluid layer  340  is formed may include an additive that reduces the surface tension thereof. To that end, polymerizable fluid layer  340  may include, as an additive, a surfactant. For purposes of this patent application, a surfactant is defined as any molecule, one tail of which is hydrophobic. Surfactants may be either fluorine containing, e.g., including a fluorine chain, or may not include any fluorine in the surfactant molecule structure.  
         [0033]     An exemplary surfactant is available under the trade name ZONYL® FSO-100 from DUPONT™ that has a general structure of R 1 R 2  where R 1 ═F(CF 2 CF 2 ) Y , with y being in a range of 1 to 7, inclusive and R 2 ═CH 2 CH   2 O(CH 2 CH 2 O) X H, where X is in a range of 0 to 15, inclusive. This provides one or more embodiments of polymerizable fluid  340  with the following composition: (a) isobornyl acrylate; (b) n-hexyl acrylate; (c) ethylene glycol diacrylate; (d) 2-hydroxy-2-methyl-1-phenyl-propan-1-one; and (e) R f CH 2 CH 2 O(CH 2 CH 2 O) X H. In accordance with one or more such embodiments, the ZONYL® FSO-100 additive comprises less than 1% of the composition, with the relative amounts of the remaining components being as discussed above. However, the percentage of ZONYL®FSO-100 may be greater than 1%. An advantage provided by the latter composition is that it may abrogate the need for an a priori release layer, i.e., a separate hydrophobic and/or low surface energy release layer disposed on imprint template  330 . Specifically, the latter composition provides desirable release properties to imprint template  330  and polymerizable fluid  340  so that polymerized layer  345  (described below) does not adhere to imprint template  330  with sufficient force to distort a feature pattern recorded therein.  
         [0034]      FIG. 5  illustrates an alternative step for that illustrated in  FIG. 3B . As shown in  FIG. 5 , instead of using planarization and transfer layer  310 , substrate  300  has been covered using any one of a number of methods that are well known to those of ordinary skill in the art with two layers, i.e., planarization and transfer layer  310   1  and planarization and transfer layer  310   2 . In accordance with one or more embodiments of the present invention, planarization and transfer layer  310   1  is a polymer containing a PMGI structure, and planarization and transfer layer  310   2  is a DUV30J-6 BARC layer that is spin coated on top of planarization and transfer layer  310   1 . In accordance with one such embodiment, (a) the polymer containing a PMGI was formed as was described above; (b) the BARC layer was cured at about 180° C. for about 60 sec; and (c) polymerizable fluid  340  was a silicon containing fluid that was formed as was described above. Advantageously, little or no interfacial mixing occurs between polymerizable fluid  340  and planarization and transfer layers  310   1  and  310   2  for such alternative embodiments.  
         [0035]     Next, as shown in  FIG. 3C , the structure shown in  FIG. 3B  is exposed to blanket actinic radiation such as, for example and without limitation, UV radiation  335 , through imprint template  330  to cross-link a substantial portion of polymerizable fluid  340  and to convert it into polymerized layer  345 . For example and without limitation, polymerizable fluid  340  was exposed for about 30 sec to UV radiation (having a wavelength of about 365 nm and having an intensity of about 15 mW/cm 2 ). It should be understood that the particular radiation employed to initiate the polymerization of polymerizable fluid  340  may be determined by one of ordinary skill in the art depending on a specific application which is desired.  
         [0036]     Next, as shown in  FIGS. 3D and 3E , imprint template  330  is withdrawn to provide high resolution, low aspect ratio relief pattern  360  that defines a residual layer  365  in polymerized layer  345 . Also note residual material  365  that may be in the form of: (1) a portion of polymerizable fluid, (2) a portion of polymerized fluid, or (3) combinations of (1) and (2). Thereafter, relief pattern  360  is anisotropically etched to remove residual layer  365  using any one of a number of methods that are well known to those of ordinary skill in the art. A selective etch is then employed to etch both polymerized layer  345  and planarization and transfer layer  310 . In accordance with one or more embodiments of the present invention, the etching selectivity of planarization and transfer layer  310  relative to polymerized layer  345  may range, for example and without limitation, from about 1.5:1 to about 100:1. Further, in accordance with one or more further embodiments of the present invention, the selective etching may be carried out by a halogen-rich (for example and without limitation, fluorine rich) reactive ion etch process. Such halogen-rich etch processes may utilize precursors such as, for example and without limitation, CHF 3  and CF 4 . In addition, planarization and transfer layer  310  has been selectively etched to substrate  300  using any one of a number of methods that are well known to those of ordinary skill in the art to provide high resolution, high aspect ratio feature pattern  370 , with the features there comprising a stacked structure  371  that includes portions of polymerized layer  345  and planarization layer  310 . In accordance with one or more further embodiments of the present invention, the selective etching may be carried out by an oxygen plasma etch process. As is well known, such etching processes may be carried out in any one of a number of apparatus that are commercially available from suppliers such as, for example and without limitation, Lam Research, Inc. of Fremont, Calif.  
         [0037]     Next,  FIG. 3F  shows aperture  380  that is a portion of high resolution, high aspect ratio feature pattern  370  illustrated in  FIG. 3E .  
         [0038]     Next, as shown in  FIGS. 3H and 3G , the sidewalls of aperture  380  have been undercut by immersion in a developer/stripper, which developer/stripper etches the sidewalls (selectively with respect to cross-linked polymerized layer  345 ) to form stacked structure  371  with an aperture  390  having a re-entrant shape. For example, a polymer containing a PMGI structure can be developed/stripped in tetramethylammonium hydroxide (TMAH) that may be obtained under the trade name CD26 from Shipley Company, L.L.C. of Marlborough, Mass. In accordance with one such embodiment of the present invention, 0.26N TMAH (i.e., 0.26 normal concentration of TMAH, where 0.26N is an industry-accepted standard concentration for TMAH developer/stripper) was used. Advantageously, in accordance with one or more embodiments, polymerized fluid  345  does not etch (i.e., dissolve) in 0.26N TMAH while a polymer containing a PMGI structure etches (i.e., dissolves) slowly therein to provide undercutting. In accordance with one or more further embodiments of the present invention, polymerized fluid  345  may also be etched in a developer/stripper used to etch planarization and transfer layer  310 . However, it is believed that better undercutting is provided when the material forming polymerized fluid  345  etches only very slowly or at a slower rate than that of the material forming planarization and transfer layer  310 .  
         [0039]     Next, as shown in  FIG. 3H , a relatively thin metal layer  395  has been blanket-deposited over the structure shown in  FIG. 5G  utilizing a reasonably directional deposition technique such as, for example and without limitation, physical vapor deposition (“PVD”) or sputtering.  
         [0040]     Next, as shown in  FIG. 3I , a lift-off process has been carried out to provide patterned metal feature  400  on substrate  300 . For example and without limitation, a polymer containing a PMGI structure can be lifted off using an N-methylpyrrolidinone (“NMP”) based stripper such as, for example and without limitation, a stripper obtained under the trade name Remover  1165  from Shipley Company, L.L.C. of Marlborough, Mass. In addition, in accordance with one such embodiment, the substrate may be processed by ultrasonic immersion in Remover  1165  at, for example and without limitation, about 50° C.  
         [0041]     Lastly, an optional final cleaning step may be performed by rinsing the wafer in IPA and blowing it dry. Optionally, this step may be followed by an oxygen plasma etching step.  
         [0042]     Although various embodiments that incorporate the teachings of the present invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings. For example and without limitation, further embodiments of the present invention exist wherein the planarization and transfer layer described above may be a high molecular weight (Mn&gt;50,000) polyhydroxystyrene. However, for such embodiments, although such a planarization and transfer layer may slightly intermix with an acrylic-based polymerizable fluid, the combination may be suitable for certain applications. In addition, although the polymerizable fluid, as described above, is an acrylic-based composition, other embodiments exist wherein this is not the case.