Abstract:
The present invention is directed to a method of forming a layer on a region of a substrate, the method including, inter alia, positioning a liquid on the substrate; and contacting the liquid with the mold, defining a gap between the mold and the substrate, with the gap enabling positioning of the liquid by capillary forces to generate the layer over the region.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of application Ser. No. 10/194,991, now U.S. Pat. No. 7,077,992, filed Jul. 11 2002, entitled Step and Repeat Imprint Lithography Processes listing Sidlgata V. Sreenivasan, Byung-Jin Choi, Norman E. Schumaker, Ronald D. Voisin, Michael P. C. Watts, and Mario J. Meissl as inventors, which application is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments presented herein relate to methods for imprint lithography. More particularly, embodiments relate to methods for micro- and nano-imprint lithography processes. 
     2. Description of the Relevant Art 
     Optical lithography techniques are currently used to make most microelectronic devices. However, it is believed that these methods are reaching their limits in resolution. Sub-micron scale lithography has been a critical process in the microelectronics industry. The use of sub-micron scale lithography allows manufacturers to meet the increased demand for smaller and more densely packed electronic circuits on chips. It is expected that the microelectronics industry will pursue structures that are as small or smaller than about 50 nm. Further, there are emerging applications of nanometer scale lithography in the areas of opto-electronics and magnetic storage. For example, photonic crystals and high-density patterned magnetic memory of the order of terabytes per square inch may require sub-100 nm scale lithography. 
     For making sub-50 nm structures, optical lithography techniques may require the use of very short wavelengths of light (e.g., about 13.2 nm). At these short wavelengths, many common materials are not optically transparent and therefore imaging systems typically have to be constructed using complicated reflective optics. Furthermore, obtaining a light source that has sufficient output intensity at these wavelengths is difficult. Such systems lead to extremely complicated equipment and processes that may be prohibitively expensive. It is also believed that high-resolution e-beam lithography techniques, though very precise, are too slow for high-volume commercial applications. 
     Several imprint lithography techniques have been investigated as low cost, high volume manufacturing alternatives to conventional photolithography for high-resolution patterning. Imprint lithography techniques are similar in that they use a template containing topography to replicate a surface relief in a film on the substrate. One form of imprint lithography is known as hot embossing. 
     Hot embossing techniques face several challenges: i) pressures greater than 10 MPa are typically required to imprint relief structures, ii) temperatures must be greater than the T g  of the polymer film, iii) patterns (in the substrate film) have been limited to isolation trenches or dense features similar to repeated lines and spaces. Hot embossing is unsuited for printing isolated raised structures, such as lines and dots. This is because the highly viscous liquids resulting from increasing the temperature of the substrate films requires extremely high pressures and long time durations to move the large volume of liquids needed to create isolated structures. This pattern dependency makes hot embossing unattractive. Also, high pressures and temperatures, thermal expansion, and material deformation generate severe technical challenges in the development of layer-to-layer alignment at the accuracies needed for device fabrication. Such pattern placement distortions lead to problems in applications, such as patterned magnetic media for storage applications. The addressing of the patterned medium bit by the read-write head becomes very challenging unless the pattern placement distortions can be kept to a minimum. 
     SUMMARY OF THE INVENTION 
     The present invention is directed towards a method of forming a layer on a region of a substrate, the method including, inter alia, positioning a liquid on the substrate; and contacting the liquid with the mold, defining a gap between the mold and the substrate, with the gap enabling positioning of the liquid by capillary forces to generate the layer over the region. These and other embodiments are discussed more fully below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the accompanying drawings in which: 
         FIG. 1  depicts an embodiment of a system for imprint lithography; 
         FIG. 2  depicts an imprint lithography system enclosure; 
         FIG. 3  depicts an embodiment of an imprint lithography head coupled to an imprint lithography system; 
         FIG. 4  depicts a projection view of an imprint head; 
         FIG. 5  depicts an exploded view of an imprint head; 
         FIG. 6  depicts a projection view of a first flexure member; 
         FIG. 7  depicts a projection view of a second flexure member; 
         FIG. 8  depicts a projection view of first and second flexure members coupled together; 
         FIG. 9  depicts a projection view of a fine orientation system coupled to a pre-calibration system of an imprint head; 
         FIG. 10  depicts a cross-sectional view of a pre-calibration system; 
         FIG. 11  depicts a schematic diagram of a flexure system; 
         FIG. 12  depicts a projection view of a motion stage and an imprint head of an imprint lithography system; 
         FIG. 13  depicts a schematic diagram of a liquid dispense system; 
         FIG. 14  depicts a projection view of an imprint head with a light source and camera optically coupled to the imprint head; 
         FIGS. 15 and 16  depict side views of an interface between a liquid droplet and a portion of a template; 
         FIG. 17  depicts a cross-sectional view of a first embodiment of template configured for liquid confinement at the perimeter of the template; 
         FIG. 18  depicts a cross-sectional view of a second embodiment of template configured for liquid confinement at the perimeter of the template; 
         FIGS. 19A-D  depict cross-sectional views of a sequence of steps of a template contacting a liquid disposed on a substrate. 
         FIGS. 20A-B  depict top and cross-sectional views, respectively, of a template having a plurality of patterning areas; 
         FIG. 21  depicts a projection view of a rigid template support system coupled to a pre-calibration system of an imprint head; 
         FIG. 22  depicts an imprint head coupled to an X-Y motion system; 
         FIGS. 23A-23F  depict cross-sectional views of a negative imprint lithography process; 
         FIGS. 24A-24D  depict cross-sectional views of a negative imprint lithography process with a transfer layer; 
         FIGS. 25A-25D  depict cross-sectional views of a positive imprint lithography process; 
         FIGS. 26A-26C  depict cross-sectional views of a positive imprint lithography process with a transfer layer; 
         FIGS. 27A-27D  depict cross-sectional views of a combined positive and negative imprint lithography process; 
         FIG. 28  depicts a schematic of an optical alignment measuring device positioned over a template and substrate; 
         FIG. 29  depicts a scheme for determining the alignment of a template with respect to a substrate using alignment marks by sequentially viewing and refocusing; 
         FIG. 30  depicts a scheme for determining the alignment of a template with respect to a substrate using alignment marks and polarized filters; 
         FIG. 31  depicts a top view of an alignment mark that is formed from polarizing lines; 
         FIGS. 32A-32C  depict top views of patterns of curable liquid applied to a substrate; 
         FIGS. 33A-33C  depict a scheme for removing a template from a substrate after curing; 
         FIG. 34  depicts an embodiment of a template positioned over a substrate for electric field based lithography; 
         FIGS. 35A-35D  depict a first embodiment of a process for forming nanoscale structures using contact with a template; 
         FIGS. 36A-36C  depict a first embodiment of a process for forming nanoscale structures without contacting a template; 
         FIGS. 37A-37B  depict a template that includes a continuous patterned conductive layer disposed on a non-conductive base; 
         FIG. 38  depicts a motion stage that includes a fine orientation system; 
         FIG. 39  depicts a motion stage having a substrate tilt module; 
         FIG. 40  depicts a schematic drawing of a substrate support; and 
         FIG. 41  depicts a schematic drawing of an imprint lithography system that includes an imprint head disposed below a substrate support. 
     
    
    
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments presented herein generally relate to systems, devices, and related processes of manufacturing small devices. More specifically, embodiments presented herein relate to systems, devices, and related processes of imprint lithography. For example, these embodiments may be used for imprinting sub-100 nm features on a substrate, such as a semiconductor wafer. It should be understood that these embodiments may also be used to manufacture other kinds of devices including, but not limited to: patterned magnetic media for data storage, micro-optical devices, micro-electro-mechanical system, biological testing devices, chemical testing and reaction devices, and X-ray optical devices. 
     Imprint lithography processes have demonstrated the ability to replicate high-resolution (e.g., sub-50 nm) images on substrates using templates that contain images as topography on their surfaces. Imprint lithography may be used in patterning substrates in the manufacture of microelectronic devices, optical devices, MEMS, opto-electronics, patterned magnetic media for storage applications, etc. Imprint lithography techniques may be superior to optical lithography for making three-dimensional structures, such as micro lenses and T-gate structures. Components of an imprint lithography system, including the template, substrate, liquid and any other materials that may affect the physical properties of the system including, but not limited to, surface energy, interfacial energies, Hamacker constants, Van der Waals&#39; forces, viscosity, density, opacity, etc., are engineered to properly accommodate a repeatable process. 
     Methods and systems for imprint lithography are discussed in U.S. Pat. No. 6,334,960 to Willson et al. entitled “Step and Flash Imprint Lithography” which is incorporated herein by reference. Additional methods and systems for imprint lithography are further discussed in U.S. patent applications: U.S. Ser. No. 09/908,455 filed Jul. 17, 2001 (published as U.S. Publication No. 2002-0094496 A1), entitled “Method and System of Automatic Fluid Dispensing for Imprint Lithography Processes”; U.S. Ser. No. 09/907,512 filed Jul. 16, 2001 (issued as U.S. Pat. No. 6,921,615) entitled “High-Resolution Overlay Alignment Methods and Systems for Imprint Lithography”; U.S. Ser. No. 09/920,341 (published as U.S. Publication No. 2002-0093122-A1) filed Aug. 1, 2001 entitled “Methods for High-Precision Gap Orientation Sensing Between a Transparent Template and Substrate for Imprint Lithography”; U.S. Ser. No. 09/934,248 filed Aug. 21, 2001 (published as U.S. Publication No. 2002-0150398-A1), entitled “Flexure Based Macro Motion Translation Stage”; U.S. Ser. No. 09/698,317 filed Oct. 27, 2000 (issued as U.S. Pat. No. 6,873,087), entitled “High-Precision Orientation Alignment and Gap Control Stages for Imprint Lithography Processes”; U.S. Ser. No. 09/976,681 filed Oct. 12, 2001 (issued as U.S. Pat. No. 6,696,220), entitled “Template Design for Room Temperature, Low Pressure Micro- and Nano-Imprint Lithography”; and U.S. Ser. No. 10/136,188 filed May 1, 2002 (published as U.S. Publication No. 2003-0205657-A1), entitled “Methods of Manufacturing a Lithography Template” all of which are incorporated herein by reference. Further methods and systems are discussed in the following publications, all of which are incorporated herein by reference: “Design of Orientation Stages for Step and Flash Imprint Lithography,” B. J. Choi, S. Johnson, M. Colburn, S. V. Sreenivasan, C. G. Willson, to appear in J. of Precision Engineering; “Large Area High Density Quantized Magnetic Disks Fabricated Using Nanoimprint Lithography,” W. Wu, B. Cui, X. Y. Sun, W. Zhang, L. Zhunag, and S. Y. Chou, J. Vac Sci Technol B 16 (6), 3825-3829, November-December 1998; “Lithographically-Induced Self-Assembly of Periodic Polymer Micropillar Arrays,” S. Y. Chou, L. Zhuang, J. Vac Sci Technol B 17 (6), 3197-3202, 1999; and “Large Area Domain Alignment in Block Copolymer Thin Films Using Electric Fields,” P. Mansky, J. DeRouchey, J. Mays, M. Pitsikalis, T. Morkved, H. Jaeger and T. Russell, Macromolecules 13, 4399 (1998) 
     System for Imprint Lithography 
     Overall System Description 
       FIG. 1  depicts an embodiment of an imprint lithography system  3900 . Imprint lithography system  3900  includes imprint head  3100 . Imprint head  3100  is mounted to an imprint head support  3910 . Imprint head  3100  is configured to hold a patterned template  3700 . Patterned template  3700  includes a plurality of recesses that define a pattern of features to be imprinted into a substrate. Imprint head  3100  or motion stage  3600  is further configured to move patterned template  3700  toward and away from a substrate to be imprinted during use. Imprint lithography system  3900  also includes motion stage  3600 . Motion stage  3600  is mounted to motion stage support  3920 . Motion stage  3600  is configured to hold a substrate and move the substrate in a generally planar motion about motion stage support  3920 . Imprint lithography system  3900  further includes an activating light source  3500  coupled to imprint head  3100 . Activating light source  3500  is configured to produce a curing light and direct the produced curing light through patterned template  3700  coupled to imprint head  3100 . Curing light includes light at an appropriate wavelength to cure a polymerizable liquid. Curing light includes ultraviolet light, visible light, infrared light, x-ray radiation and electron beam radiation. 
     Imprint head support  3910  is coupled to motion stage support  3920  by bridging supports  3930 . In this manner imprint head  3100  is positioned above motion stage  3600 . Imprint head support  3910 , motion stage support  3920  and bridging supports  3930  are herein collectively referred to as the system “body.” The components of the system body may be formed from thermally stable materials. Thermally stable materials have a thermal expansion coefficient of less than about 10 ppm/° C. at about room temperature (e.g., 25° C.). In some embodiments, the material of construction may have a thermal expansion coefficient of less than about 10 ppm/° C., or less than 1 ppm/° C. Examples of such materials include silicon carbide, certain alloys of iron including, but not limited to, certain alloys of steel and nickel (e.g., alloys commercially available under the name INVAR®), and certain alloys of steel, nickel and cobalt (e.g., alloys commercially available under the name SUPER INVAR™). Additional examples of such materials include certain ceramics including, but not limited to, ZERODUR® ceramic. Motion stage support  3920  and bridging supports  3930  are coupled to support table  3940 . Support table  3940  provides a substantially vibration free support for the components of imprint lithography system  3900 . Support table  3940  isolates imprint lithography system  3900  from ambient vibrations (e.g., due to works, other machinery, etc.). Motion stages and vibration isolation support tables are commercially available from Newport Corporation of Irvine, Calif. 
     As used herein, the “X-axis” refers to the axis that runs between bridging supports  3930 . As used herein the “Y-axis” refers to the axis that is orthogonal to the X-axis. As used herein the “X-Y plane” is a plane defined by the X-axis and the Y-axis. As used herein the “Z-axis” refers to an axis running from motion stage support  3920  to imprint head support  3910 , orthogonal to the X-Y plane. Generally an imprint process involves moving the substrate, or imprint head  3100 , along an X-Y plane until the proper position of the substrate with respect to patterned template  3700  is achieved. Movement of patterned template  3700 , or motion stage  3600 , along the Z-axis, will bring patterned template  3700  to a position that allows contact between patterned template  3700  and a liquid disposed on a surface of the substrate. 
     Imprint lithography system  3900  may be placed in an enclosure  3960 , as depicted in  FIG. 2 . Enclosure  3960  encompasses imprint lithography system  3900  and provides a thermal and air barrier to the lithography components. Enclosure  3960  includes movable access panel  3962  that allows access to the imprint head  3100  and motion stage  3600  when moved to an “open” position, as depicted in  FIG. 2 . When in a “closed” position, the components of imprint lithography system  3900  are at least partially isolated from the room atmosphere. Access panel  3962  also serves as a thermal barrier to reduce the effects of temperature changes within the room on the temperature of the components within enclosure  3960 . Enclosure  3960  includes a temperature control system. A temperature control system is used to control the temperature of components within enclosure  3960 . In one embodiment, a temperature control system is configured to inhibit temperature variations of greater than about 10° C. within enclosure  3960 . In some embodiments, a temperature control system inhibits variations of greater than about 0.1° C. In one embodiment, thermostats or other temperature measuring devices in combination with one or more fans may be used to maintain a substantially constant temperature within enclosure  3960 . 
     Various user interfaces may also be present on enclosure  3960 . A computer controlled user interface  3964  may be coupled to enclosure  3960 . User interface  3964  may depict the operating parameters, diagnostic information, job progress and other information related to the functioning of enclosed imprint lithography system  3900 . User interface  3964  may also be configured to receive operator commands to alter the operating parameters of imprint lithography system  3900 . A staging support  3966  may also be coupled to enclosure  3960 . Staging support  3966  is used by an operator to support substrates, templates and other equipment during an imprint lithography process. In some embodiments, staging support  3966  may include one or more indentations  3967  configured to hold a substrate (e.g., a circular indentation for a semiconductor wafer). Staging support  3966  may also include one or more indentations  3968  for holding a patterned template  3700 . 
     Additional components may be present depending on the processes that the imprint lithography system  3900  is designed to implement. For example, for semiconductor processing equipment including, but not limited to, an automatic wafer loader, an automatic template loader and an interface to a cassette loader (all not shown), may be coupled to imprint lithography system  3900 . 
     Imprint Head 
       FIG. 3  depicts an embodiment of a portion of an imprint head  3100 . Imprint head  3100  includes a pre-calibration system  3109  and a fine orientation system  3111  coupled to pre-calibration system  3109 . Template support  3130  is coupled to fine orientation system  3111 . Template support  3130  is designed to support and couple patterned template  3700  to fine orientation system  3111 . 
     Referring to  FIG. 4 , a disk-shaped flexure ring  3124 , which makes up a portion of pre-calibration system  3109  is coupled to imprint head housing  3120 . Imprint head housing  3120  is coupled to a middle frame  3114  with guide shafts  3112   a  and  3112   b . In one embodiment, three (3) guide shafts may be used (the back guide shaft is not visible in  FIG. 4 ) to provide a support for housing  3120 . Sliders  3116   a  and  3116   b  coupled to corresponding guide shafts  3112   a  and  3112   b  about middle frame  3114  are used to facilitate the up and down motion of housing  3120 . A disk-shaped base plate  3122  is coupled to the bottom portion of housing  3120 . Base plate  3122  may be coupled to flexure ring  3124 . Flexure ring  3124  supports fine orientation system  3111  components that include first flexure member  3126  and second flexure member  3128 . The operation and configuration of flexure members  3126  and  3128  are discussed in detail below. 
       FIG. 5  depicts an exploded view of imprint head  3100 . As shown in  FIG. 5 , actuators  3134   a ,  3134   b  and  3134   c  are fixed within housing  3120  and coupled to base plate  3122  and flexure ring  3124 . In operation, motion of actuators  3134   a ,  3134   b , and  3134   c  controls the movement of flexure ring  3124 . Motion of actuators  3134   a ,  3134   b  and  3134   c  may allow for a coarse pre-calibration. In some embodiments, actuators  3134   a ,  3134   b  and  3134   c  may be equally spaced around housing  3120 . Actuators  3134   a ,  3134   b ,  3134   c  and flexure ring  3124  together form pre-calibration system  3109 . Actuators  3134   a ,  3134   b , and  3134   c  allow translation of flexure ring  3124  along the Z-axis to control the gap accurately. 
     Imprint head  3100  also includes a mechanism that enables fine orientation control of patterned template  3700  so that proper orientation alignment may be achieved and a uniform gap may be maintained by the template with respect to a substrate surface. Alignment and gap control is achieved, in one embodiment, by the use of first and second flexure members,  3126  and  3128 , respectively. 
       FIGS. 6 and 7  depict embodiments of first and second flexure members,  3126  and  3128 , respectively, in more detail. As depicted in  FIG. 6 , first flexure member  3126  includes a plurality of flexure joints  3160  coupled to corresponding rigid bodies  3164  and  3166 . Flexure joints  3160  may be notch shaped to provide motion of rigid bodies  3164  and  3166  about pivot axes that are located along the thinnest cross section of the flexure joints. Flexure joints  3160  and rigid body  3164  together form arm  3172 , while additional flexure joints  3160  and rigid body  3166  together form arm  3174 . Arms  3172  and  3174  are coupled to and extend from first flexure frame  3170 . First flexure frame  3170  has an opening  3182 , which allows curing light (e.g., ultraviolet light) to pass through first flexure member  3126 . In the depicted embodiment, four flexure joints  3160  allow motion of first flexure frame  3170  about a first orientation axis  3180 . It should be understood, however, that more or less flexure joints might be used to achieve the desired control. First flexure member  3126  is coupled to second flexure member  3128  through first flexure frame  3170 , as depicted in  FIG. 8 . First flexure member  3126  also includes two coupling members  3184  and  3186 . Coupling members  3184  and  3186  include openings that allow attachment of the coupling members to flexure ring  3124  using any suitable fastening means. Coupling members  3184  and  3186  are coupled to first flexure frame  3170  via arms  3172  and  3174 , as depicted in  FIG. 6 . 
     Second flexure member  3128  includes a pair of arms  3202  and  3204  extending from second flexure frame  3206 , as depicted in  FIG. 7 . Flexure joints  3162  and rigid body  3208  together form arm  3202 , while additional flexure joints  3162  and rigid body  3210  together form arm  3204 . Flexure joints  3162  may be notch shaped to provide motion of rigid body  3210  and arm  3204  about pivot axes that are located along the thinnest cross-section of the flexure joints  3162 . Arms  3202  and  3204  are coupled to and extend from template support  3130 . Template support  3130  is configured to hold and retain at least a portion of a patterned template  3700 . Template support  3130  also has opening  3212 , which allows curing light (e.g., ultraviolet light) to pass through second flexure member  3128 . In the depicted embodiment, four flexure joints  3162  allow motion of template support  3130  about a second orientation axis  3200 . It should be understood, however, that more or less flexure joints may be used to achieve the desired control. Second flexure member  3128  also includes braces  3220  and  3222 . Braces  3220  and  3222  include openings that allow attachment of the braces to portions of first flexure member  3126 . 
     In one embodiment, first flexure member  3126  and second flexure member  3128  are joined as shown in  FIG. 8  to form fine orientation system  3111 . Braces  3220  and  3222  are coupled to first flexure frame  3170  such that first orientation axis  3180  of first flexure member  3126  and second orientation axis  3200  of second flexure member  3128  are substantially orthogonal to each other. In such a configuration, first orientation axis  3180  and second orientation axis  3200  intersect at a pivot point  3252  at approximately the center region of a patterned template  3700  disposed in template support  3130 . This coupling of the first and second flexure members,  3126  and  3128 , respectively, allows fine alignment and gap control of patterned template  3700  during use. While the first and second flexure members,  3126  and  3128 , are depicted as discrete elements, it should be understood that the first and second flexure members,  3126  and  3128 , respectively, may be formed from a single machined part where the flexure members  3126  and  3218  are integrated together. Flexure members  3126  and  3128  are coupled by mating of surfaces such that motion of patterned template  3700  occurs about pivot point  3252 , substantially reducing “swinging” and other motions that may shear imprinted features following imprint lithography. Fine orientation system  3111  imparts negligible lateral motion at the template surface and negligible twisting motion about the normal to the template surface due to selectively constrained high structural stiffness of the flexure joints  3162 . Another advantage of using the herein described flexure members is that they do not generate substantial amounts of particles, especially when compared with frictional joints. This offers an advantage for imprint lithography processes, as particles may disrupt such processes. 
       FIG. 9  depicts the assembled fine orientation system  3111  coupled to pre-calibration system  3109 . Patterned template  3700  is positioned within template support  3130  that is part of second flexure member  3128 . Second flexure member  3128  is coupled to first flexure member  3126  in a substantially orthogonal orientation. First flexure member  3126  is coupled to flexure ring  3124  via coupling members  3186  and  3184 . Flexure ring  3124  is coupled to base plate  3122 , as has been described above. 
       FIG. 10  represents a cross-section of the pre-calibration system  3109  looking through cross-section  3260 . As shown in  FIG. 10 , flexure ring  3124  is coupled to base plate  3122  with actuator  3134 . Actuator  3134  includes an end  3270  coupled to a force detector  3135  that contacts flexure ring  3124 . During use activation of actuator  3134  causes movement of end  3270  toward or away from flexure ring  3124 . The movement of end  3270  toward flexure ring  3124  induces a deformation of flexure ring  3124  and causes translation of the fine orientation system  3111  along the Z-axis toward the substrate. Movement of end  3270  away from flexure ring  3124  allows flexure ring  3124  to move to its original shape and, in the process, moves fine orientation system  3111  away from the substrate. 
     In a typical imprint process patterned template  3700  is disposed in a template support  3130  coupled to fine orientation system  3111 , as depicted in previous figures. Patterned template  3700  is brought into contact with a liquid on a surface of a substrate. Compression of the liquid on the substrate as patterned template  3700  is brought closer to the substrate causes a resistive force to be applied by the liquid onto the template. This resistive force is translated through fine orientation system  3111  and to flexure ring  3124 , as shown in both  FIGS. 9 and 10 . The force applied against flexure ring  3124  will also be translated as a resistive force to actuator  3134 . The resistive force applied to actuator  3134  may be determined using force sensor  3135 . Force detector  3135  may be coupled to actuator  3134  such that a resistive force applied to actuator  3134  during use may be determined and controlled. 
       FIG. 11  depicts a flexure model  3300 , useful in understanding the principles of operation of a fine decoupled orientation stage, such as fine orientation system  3111  described herein. Flexure model  3300  may include four parallel joints: Joints  1 ,  2 ,  3  and  4 , that provide a four-bar linkage system in its nominal and rotated configurations. Line  3310  denotes an axis of alignment of Joints  1  and  2 . Line  3312  denotes an axis of alignment of Joints  3  and  4 . Angle {acute over (α)} 1  represents an angle between a perpendicular axis through the center of patterned template  3700  and line  3310 . Angle {acute over (α)} 2  represents a perpendicular axis through the center of patterned template  3700  and line  3310 . Angles {acute over (α)} 1  and {acute over (α)} 2 , in some embodiments, are selected so that the compliant alignment axis (or orientation axis) lies substantially at the surface of patterned template  3700 . For fine orientation changes, rigid body  3314  between Joints  2  and  3  may rotate about an axis depicted by Point C. Rigid body  3314  may be representative of template support  3130  of second flexure member  3128 . 
     Fine orientation system  3111  generates pure tilting motions with no substantial lateral motions at the surface of patterned template  3700  coupled to fine orientation system  3111 . The use of flexure arms  3172 ,  3174 ,  3202  and  3204  may provide fine orientation system  3111  with high stiffness in the directions where side motions or rotations are undesirable and lower stiffness in directions where necessary orientation motions are desirable. Fine orientation system  3111 , therefore, allows rotations of template support  3130 , and therefore patterned template  3700 , about pivot point  3252  at the surface of patterned template  3700 , while providing sufficient resistance in a direction perpendicular to patterned template  3700  and parallel to patterned template  3700  to maintain the proper position with respect to the substrate. In this manner a passive orientation system is used for orientation of patterned template  3700  to a parallel orientation with respect to patterned template  3700 . The term “passive” refers to a motion that occurs without any user or programmable controller intervention, i.e., the system self-corrects to a proper orientation by contact of patterned template  3700  with the liquid. Alternate embodiments in which the motion of flexure arms  3172 ,  3174 ,  3202  and  3204  are controlled by motors to produce an active flexure may also be implemented. 
     Motion of fine orientation system  3111  may be activated by direct or indirect contact with the liquid. If fine orientation system  3111  is passive, then it is, in one embodiment, designed to have the most dominant compliance about two orientation axes. The two orientation axes lie orthogonal to each other and lie on the imprinting surface of an imprinting member disposed on fine orientation system  3111 . The two orthogonal torsional compliance values are set to be the same for a symmetrical imprinting member. A passive fine orientation system  3111  is designed to alter the orientation of patterned template  3700  when patterned template  3700  is not parallel with respect to a substrate. When patterned template  3700  makes contact with liquid on the substrate, the flexure members  3126  and  3128  compensate for the resulting uneven liquid pressure on patterned template  3700 . Such compensation may be affected with minimal or no overshoot. Further, a fine orientation system  3111  as described above may hold the substantially parallel orientation between patterned template  3700  and the substrate for a sufficiently long period to allow curing of the liquid. 
     Imprint head  3100  is mounted to imprint head support  3910  as depicted in  FIG. 1 . In this embodiment, imprint head support  3910  is mounted such that imprint head  3100  remains in a fixed position at all times. During use, all movement along the X-Y plane is performed to the substrate by motion stage  3600 . 
     Motion Stage 
     Motion stage  3600  is used to support a substrate to be imprinted and move the substrate along an X-Y plane during use. Motion stage  3600 , in some embodiments, is capable of moving a substrate over distances of up to several hundred millimeters with an accuracy of at least ±30 nm, preferably with an accuracy of about ±10 nm. In one embodiment, motion stage  3600  includes a substrate chuck  3610  that is coupled to carriage  3620 , as depicted in  FIG. 12 . Carriage  3620  is moved about a base  3630  on a frictional bearing system or a non-frictional bearing system. In one embodiment, a non-frictional bearing system that includes an air bearing is used. Carriage  3620  is suspended above base  3630  of motion stage  3600  using, in one embodiment, an air layer (i.e., the “air bearing”). Magnetic or vacuum systems may be used to provide a counter balancing force to the air bearing level. Both magnetic based and vacuum based systems are commercially available from a variety of suppliers and any such systems may be used in an imprint lithography process. One example of a motion stage  3600  that is applicable to imprint lithography processes is the Dynam YX motion stage  3600  commercially available from Newport Corporation, Irvine Calif. Motion stage  3600  also may include a tip tilt stage similar to the calibration stage, designed to approximately level the substrate to the X-Y motion plane. It also may include one or more theta stages to orient the patterns on the substrate to the X-Y motion axes. 
     Liquid Dispenser 
     Imprint lithography system  3900  also includes a liquid dispense system  3125  which is used to dispense a curable liquid onto a substrate. Liquid dispense system  3125  is coupled to the system body. In one embodiment, a liquid dispense system is coupled to imprint head  3100 .  FIG. 3  depicts liquid dispenser head  2507  of liquid dispense system  3125  extending out from cover  3127  of imprint head  3100 . Various components of liquid dispense system  3125  may be disposed in cover  3127  of imprint head  3100 . 
     A schematic of liquid dispense system  3125  is depicted in  FIG. 13 . In an embodiment, liquid dispense system  3125  includes liquid container  2501 . Liquid container  2501  is configured to hold an activating light curable liquid. Liquid container  2501  is coupled to pump  2504  via inlet conduit  2502 . An inlet valve  2503  is positioned between liquid container  2501  and pump  2504  to control flow of through inlet conduit  2502 . Pump  2504  is coupled to liquid dispenser head  2507  via outlet conduit  2506 . 
     Liquid dispense system  3125  is configured to allow precise volume control of the amount of liquid dispensed onto an underlying substrate. In one embodiment, liquid control is achieved using a piezoelectric valve as pump  2504 . Piezoelectric valves are available commercially available from the Lee Company, Westbrook, Conn. During use, a curable liquid is drawn into pump  2504  through inlet conduit  2502 . When a substrate is properly positioned below, pump  2504  is activated to force a predetermined volume of liquid through outlet conduit  2506 . The liquid is then dispensed through liquid dispenser head  2507  onto the substrate. In this embodiment, liquid volume control is achieved by control of pump  2504 . Rapid switching of pump  2504  from an open to closed state allows a controlled amount of liquid to be sent to liquid dispenser head  2507 . Pump  2504  is configured to dispense liquid in volumes of less than about 1 μL. The operation of pump  2504  may allow either droplets of liquid or a continuous pattern of liquid to be dispensed onto the substrate. Droplets of liquid are applied by rapidly cycling pump  2504  from an open to closed state. A stream of liquid is produced on the substrate by leaving pump  2504  in an open state and moving the substrate under liquid dispenser head  2507 . 
     In another embodiment, liquid volume control may be achieved by use of liquid-to-liquid dispenser head  2507 . In such a system, pump  2504  is used to supply a curable liquid dispenser head  2507 . Small drops of liquid whose volume may be accurately specified are dispensed using a liquid dispensing actuator. Examples of liquid dispensing actuators include microsolenoid valves or piezo-actuated dispensers. Piezo-actuated dispensers are commercially available from MicroFab Technologies, Inc., Plano, Tex. Liquid dispensing actuators are incorporated into liquid dispenser head  2507  to allow control of liquid dispensing. Liquid dispensing actuators are configured to dispense between about 50 ρL to about 1000 ρL of liquid per drop of liquid dispensed. Advantages of a system with a liquid dispensing actuator include faster dispensing time and more accurate volume control. Liquid dispensing systems are further described in U.S. application Ser. No. 09/908,455 filed Jul. 17, 2001, (now U.S. Publication No. 2002-0094496-A1) entitled “Method and System of Automatic Fluid Dispensing for Imprint Lithography Processes,” which is incorporated herein by reference. 
     Coarse Measurement System 
     Coarse determination of the position of patterned template  3700  and the substrate is determined by the use of linear encoders (e.g., exposed linear encoders). Encoders offer a coarse measurement on the order of 0.01 μm. Linear encoders include a scale coupled to the moving object and a reader coupled to the body. The scale may be formed from a variety of materials including glass, glass ceramics, and steel. The scale includes a number of markings that are read by the reader to determine a relative or absolute position of the moving object. The scale is coupled to motion stage  3600  by means that are known in the art. A reader is coupled to the body and optically coupled to the scale. In one embodiment, an exposed linear encoder may be used. Encoders may be configured to determine the position of motion stage  3600  along either a single axis, or in a two-axis plane. An example of an exposed two-axis linear encoder is the PP model encoder available from Heidenhain Corporation, Schaumburg, Ill. Generally, encoders are built into many commercially available X-Y motion stages. For example, the Dynam YX motion stage available from Newport Corp. has a two-axis encoder built into the system. 
     The coarse position of patterned template  3700  along the Z-axis is also determined using a linear encoder. In one embodiment, an exposed linear encoder may be used to measure the position of patterned template  3700 . A scale of the linear encoder, in one embodiment, is coupled to the pre-calibration ring of imprint head  3100 . Alternatively, the scale may be coupled directly to template support  3130 . The reader is coupled to the body and optically coupled to the scale. Position of patterned template  3700  is determined along the Z-axis by use of encoders. 
     Air Gauges 
     In an embodiment, air gauge  3135  may be coupled to imprint head  3100 , as depicted in  FIG. 3 . Air gauge  3135  is used to determine whether a substrate disposed on motion stage  3600  is substantially parallel to a reference plane. As used herein, an “air gauge” refers to a device that measures the pressure of a stream of air directed toward a surface. When a substrate is disposed under an outlet of air gauge  3135 , the distance the substrate is from the outlet of air gauge  3135  will influence the pressure air gauge  3135  senses. Generally, the further away from air gauge  3135  the substrate is, the lesser the pressure. 
     In such a configuration, air gauge  3135  may be used to determine differences in pressure resulting from changes in the distance between the substrate surface and air gauge  3135 . By moving air gauge  3135  along the surface of the substrate, air gauge  3135  determines the distance between air gauge  3135  and the substrate surface at the various points measured. The degree of planarity of the substrate with respect to air gauge  3135  is determined by comparing the distance between air gauge  3135  and the substrate at the various points measured. The distance between at least three points on the substrate and air gauge  3135  is used to determine if a substrate is planar. If the distance is substantially the same, the substrate is considered to be planar. Significant differences in the distances measured between the substrate and air gauge  3135  indicates a non-planar relationship between the substrate and air gauge  3135 . This non-planar relationship may be caused by the non-planarity of the substrate or a tilt of the substrate. Prior to use, a tilt of the substrate is corrected to establish a planar relationship between the substrate and patterned template  3700 . Suitable air gauges may be obtained from Senex Inc. 
     During use of air gauges, the substrate or patterned template  3700  is placed within the measuring range of air gauge  3135 . Motion of the substrate toward air gauge  3135  may be accomplished by either Z-axis motion of imprint head  3100  or Z-axis motion of motion stage  3600 . 
     Light Source 
     In an imprint lithography process, a light curable liquid is disposed on a surface of the substrate. Patterned template  3700  is brought into contact with the light curable liquid and activating light is applied to the light curable liquid. As used herein “activating light” means light that may affect a chemical change. Activating light may include ultraviolet light (e.g., light having a wavelength between about 200 nm to about 400 nm), actinic light, visible light or infrared light. Generally, any wavelength of light capable of affecting a chemical change may be classified as activating. Chemical changes may be manifested in a number of forms. A chemical change may include, but is not limited to, any chemical reaction that causes a polymerization or a cross-linking reaction to take place. The activating light, in one embodiment, is passed through patterned template  3700  prior to reaching the composition. In this manner the light curable liquid is cured to form structures complementary to the structures formed on patterned template  3700 . 
     In some embodiments, activating light source  3500  is an ultraviolet light source capable of producing light having a wavelength between about 200 nm to about 400 nm. Activating light source  3500  is optically coupled to patterned template  3700  as depicted in  FIG. 1 . In one embodiment, activating light source  3500  is positioned proximate to imprint head  3100 . Imprint head  3100  includes a mirror  3121 , as depicted in  FIG. 4 , which reflects light from activating light source  3500  to patterned template  3700 . Light passes through an opening in the body of imprint head  3100  and is reflected by mirror  3121  toward patterned template  3700 . In this manner, activating light source  3500  irradiates patterned template  3700  without being disposed in imprint head  3100 . 
     Most activating light sources produce a significant amount of heat during use. If activating light source  3500  is too close to imprint lithography system  3900 , heat from light source  3700  will radiate toward the body of imprint lithography system  3900  and may cause the temperature of portions of the body to increase. Since many metals expand when heated, the increase in temperature of a portion of the body of imprint lithography system  3900  may cause the body to expand. This expansion may affect the accuracy of imprint lithography system  3900  when sub-100 nm features are being produced. 
     In one embodiment, activating light source  3500  is positioned at a sufficient distance from the body such that the system body is insulated from heat produced by activating light source  3500  by the intervening air between activating light source  3500  and imprint head  3100 .  FIG. 14  depicts activating light source  3500  optically coupled to imprint head  3100 . Activating light source  3500  includes an optical system  3510  that projects light generated by a light source toward imprint head  3100 . Light passes from optical system  3510  into imprint head  3100  via opening  3123 . Light is then reflected toward a template coupled to imprint head  3100  by mirror  3121  disposed within imprint head  3100  (see  FIG. 4 ). In this manner, the light source is thermally insulated from the body. A suitable light source may be obtained from OAI Inc., Santa Clara, Calif. 
     Optical Alignment Devices 
     One or more optical measuring devices may be optically coupled to imprint head  3100  and/or motion stage  3600 . Generally, an optical measuring device is any device that allows the position and/or orientation of patterned template  3700  with respect to a substrate to be determined. 
     Turning to  FIG. 14 , a through the template optical imaging system  3800  is optically coupled to imprint head  3100 . Optical imaging system  3800  includes optical imaging device  3810  and optical system  3820 . Optical imaging device  3810 , in one embodiment, is a CCD microscope. Optical imaging system  3810  is optically coupled to patterned template  3700  through imprint head  3100 . Optical imaging system  3800  is also optically coupled to a substrate, when the substrate is disposed under patterned template  3700 . Optical imaging system  3800  is used to determine the placement error between patterned template  3700  and an underlying substrate as described herein. In one embodiment, mirror  3121  (see  FIG. 4 ) is movable within imprint head  3100 . During an alignment or optical inspection process, mirror  3121  is moved out of the optical path of the optical imaging system. 
     During use of an optical alignment device, the substrate or patterned template  3700  is placed within the measuring range (e.g., the field of view) of the air optical imaging system. Motion of the substrate toward the optical imaging system  3800  may be accomplished by either Z-axis motion of imprint head  3100  or Z-axis motion of motion stage  3600 . 
     Light Curable Liquid 
     As previously mentioned, a light curable liquid is placed on a substrate and a template is brought into contact with the liquid during an imprint lithography process. The curable liquid is a low viscosity liquid monomer solution. A suitable solution may have a viscosity ranging from about 0.01 cps to about 100 cps (measured at 25° C.). Low viscosities are especially desirable for high-resolution (e.g., sub-100 nm) structures. Low viscosities also lead to faster gap closing. Additionally, low viscosities result in faster liquid filling of the gap area at low pressures. In particular, in the sub-50 nm regime, the viscosity of the solution should be at or below about 30 cps, or more preferably below about 5 cps (measured at 25° C). 
     Many of the problems encountered with other lithography techniques may be solved by using a low viscosity light curable liquid in an imprint lithography process. Patterning of low viscosity light curable liquids solves each of the issues facing hot embossing techniques by utilizing a low-viscosity, light-sensitive liquid. Also use of a thick, rigid, transparent template offers the potential for easier layer-to-layer alignment. The rigid template is, in general, transparent to both liquid activating light and alignment mark measurement light. 
     The curable liquid may be composed of a variety of polymerizable materials. Generally, any photopolymerizable material may be used. Photopolymerizable materials may include a mixture of monomers and a photoinitiator. In some embodiments, the curable liquid may include one or more commercially available negative photoresist materials. The viscosity of the photoresist material may be reduced by diluting the liquid photoresist with a suitable solvent. 
     In an embodiment, a suitable curable liquid includes a monomer, a silylated monomer, and an initiator. A crosslinking agent and a dimethyl siloxane derivative may also be included. Monomers include, but are not limited to, acrylate and methacylate monomers. Examples of monomers include, but are not limited to, butyl acrylate, methyl acrylate, methyl methacrylate, or mixtures thereof. The monomer makes up approximately 25 to 50% by weight of the curable liquid. It is believed that the monomer ensures adequate solubility of the photoinitiator in the curable liquid. It is further believed that the monomer provides adhesion to an underlying organic transfer layer, when used. 
     The curable liquid may also include a silylated monomer. Silylated monomers in general are polymerizable compounds that include a silicon group. Classes of silylated monomers include, but are not limited to, silane acrylyl and silane methacrylyl derivatives. Specific examples include methacryloxypropyl tris(tri-methylsiloxy)silane and (3-acryloxypropyl)tris(trimethoxysiloxy)-silane. Silylated monomers may be present in amounts from 25 to 50% by weight. The curable liquid may also include a dimethyl siloxane derivative. Examples of dimethyl siloxane derivatives include, but are not limited to, (acryloxypropyl) methylsiloxane dimethylsiloxane copolymer, acryloxypropyl methylsiloxane homopolymer, and acryloxy terminated polydimethylsiloxane. Dimethyl siloxane derivatives are present in amounts from about 0 to 50% by weight. It is believed that the silylated monomers and the dimethyl siloxane derivatives may impart a high oxygen etch resistance to the cured liquid. Additionally, both the silylated monomers and the dimethyl siloxane derivatives are believed to reduce the surface energy of the cured liquid, therefore increasing the ability of the template to release from the surface. The silylated monomers and dimethyl siloxane derivatives listed herein are all commercially available from Gelest, Inc. 
     Any material that may initiate a free radical reaction may be used as the initiator. For activating light curing of the curable material, it is preferred that the initiator is a photoinitiator. Examples of initiators include, but are not limited to, alpha-hydroxyketones (e.g., 1-hydroxycyclohexyl phenyl ketone, sold by Ciba-Geigy Specialty Chemical Division as Irgacure 184), and acylphosphine oxide initiators (e.g., phenylbis(2,4,6-trimethyl benzoyl)phosphine oxide, sold by Ciba-Geigy Specialty Chemical Division as Irgacure 819). 
     The curable liquid may also include a crosslinking agent. Crosslinking agents are monomers that include two or more polymerizable groups. In one embodiment, polyfunctional siloxane derivatives may be used as a crosslinking agent. An example of a polyfunctional siloxane derivative is 1,3-bis(3-methacryloxypropyl)-tetramethyl disiloxane. 
     In one example, a curable liquid may include a mixture of 50% by weight of n-butyl acrylate and 50% (3-acryloxypropyl)tris-trimethylsiloxane-silane. To this mixture 3% by weight mixture of a 1:1 Irgacure 819 and Irgacure 184 and 5% of the crosslinker 1,3-bis(3-methacryloxypropyl)-tetramethyl disiloxane may be added. The viscosity of this mixture is less than 30 cps measured at about 25° C. 
     Curable Liquid with Gas Release 
     In an alternate embodiment, the curable liquid may be formed of a monomer, an acid-generating photo-agent, and a base-generating photo-agent. Examples of the monomer include, but are not limited to, phenolic polymers and epoxy resins. The acid-generating photo-agent is a compound that releases acid when treated with activating light. The generated acid catalyzes polymerization of the monomer. Those of ordinary skill in the art know such acid-generating additives, and the specific acid-generating additive used depends on the monomer and the desired curing conditions. In general, the acid-generating additive is selected to be sensitive to radiation at the first wavelength λ 1 , which, in some implementations, is in the visible or near ultraviolet (near UV) range. For example, in some implementations, the first wavelength λ 1  is selected to be approximately 400 nm or longer. A base generating photo-agent is also added to the monomer. The base-generating photo-agent may inhibit curing of the monomer near the interface of the template. The base generating photo-agent may be sensitive to radiation at a second wavelength λ 2 , yet inert or substantially inert to radiation at the first wavelength λ 1 . Moreover, the second wavelength λ 2  should be selected so that radiation at the second wavelength is primarily absorbed near the surface of the monomer at the interface with the template and does not penetrate very far into the curable liquid. For example, in some implementations, a base generating additive that is sensitive to radiation having a wavelength λ 2  in the deep UV range, in other words, radiation having a wavelength in the range of about 190-280 nm, may be used. 
     According to an embodiment, a curable liquid that includes a monomer, an acid-generating photo-agent and a base-generating photo-agent is deposited onto a substrate. A template is brought into contact with the curable liquid. The curable liquid is then exposed to radiation at a first wavelength λ 1  and a second wavelength λ 2  of light at substantially the same time. Alternatively, the curing liquid may be exposed to the radiation at the second wavelength λ 2  and subsequently to the radiation at the first wavelength λ 1 . Exposure of the curable liquid to radiation at the second wavelength λ 2  produces an excess of base near the interface with the template. The excess base serves to neutralize the acid that is produced by exposure of the curable liquid to radiation at the first wavelength. λ 1 , thereby inhibiting the acid from curing the curable liquid. Since the radiation at the second wavelength λ 2  has a shallow penetration depth into the curable liquid, the base produced by that radiation only inhibits curing of the curable liquid at or near the interface with the template. The remainder of the curable liquid is cured by exposure to the longer wavelength radiation (λ 1 ) which penetrates throughout the curable liquid. U.S. Pat. No. 6,218,316 entitled “Planarization of Non-Planar Surfaces in Device Fabrication” describes additional details concerning this process and is incorporated herein by reference. 
     In another embodiment, the curable liquid may include a photosensitive agent which, when exposed, for example, to deep UV radiation, decomposes to produce one or more gases, such as hydrogen (H 2 ), nitrogen (N 2 ), nitrous oxide (N 2 O), sulfur tri-oxide (SO 3 ), acetylene (C 2 H 2 ), carbon dioxide (CO 2 ), ammonia (NH 3 ) or methane (CH 4 ). Radiation at a first wavelength λ 2 , such as visible or near UV, may be used to cure the curable liquid, and the deep UV radiation (λ 2 ) may be used to produce one or more of the foregoing gases. The generation of the gases produces localized pressure near the interface between the cured liquid and the template to facilitate separation of the template from the cured liquid. U.S. Pat. No. 6,218,316 describes additional details concerning this process and is incorporated herein by reference. 
     In another embodiment, a curable liquid may be composed of a monomer that cures to form a polymer that may be decomposed by exposure to light. In one embodiment, a polymer with a doubly substituted carbon backbone is deposited on the substrate. After the template is brought into contact with the curable liquid, the curable liquid is exposed to radiation at a first wavelength λ 1  (e.g., greater than 400 nm) and radiation at the second wavelength λ 2  in the deep UV range. Radiation at the first wavelength serves to cure the curable liquid. When the curable liquid is exposed to the second wavelength λ 2 , scission occurs at the substituted carbon atoms. Since deep UV radiation does not penetrate deeply into the curable liquid, the polymer decomposes only near the interface with the template. The decomposed surface of the cured liquid facilitates separation from the template. Other functional groups which facilitate the photo-decomposition of the polymer also can be used. U.S. Pat. No. 6,218,316 describes additional details concerning this process and is incorporated herein by reference. 
     Patterned Templates 
     In various embodiments, an imprint lithography template is manufactured using processes including, but not limited to: optical lithography, electron beam lithography, ion-beam lithography, x-ray lithography, extreme ultraviolet lithography, scanning probe lithography, focused ion beam milling, interferometric lithography, epitaxial growth, thin film deposition, chemical etch, plasma etch, ion milling, reactive ion etch or a combination of the above. Methods for making patterned templates are described in U.S. patent application Ser. No. 10/136,188 filed May 1, 2002 (published as U.S. Publication No 2003-0205657) entitled “Methods of Manufacturing a Lithography Template” which is incorporated herein by reference. 
     In an embodiment, the imprint lithography template is substantially transparent to activating light. The template includes a body having a lower surface. The template further includes a plurality of recesses on the lower surface extending toward the top surface of the body. The recesses may be of any suitable size, although typically at least a portion of the recesses has a feature size of less than about 250 nm. 
     With respect to imprint lithography processes, the durability of the template and its release characteristics may be of concern. In one embodiment, a template is formed from quartz. Other materials may be used to form the template and include, but are not limited to: silicon germanium carbon, gallium nitride, silicon germanium, sapphire, gallium arsinide, epitaxial silicon, poly-silicon, gate oxide, silicon dioxide or combinations thereof. Templates may also include materials used to form detectable features, such as alignment markings. For example, detectable features may be formed of SiO x , where X is less than 2. In some embodiments, X is about 1.5. In another example, detectable features may be formed of a molybdenum silicide. Both SiO x  and molybdenum silicide are optically transparent to light used to cure the polymerizable liquid. Both materials, however, are substantially opaque to visible light. Use of these materials allows alignment marks to be created on the template that will not interfere with curing of the underlying substrate. 
     As previously mentioned, the template is treated with a surface treatment material to form a thin layer on the surface of the template. A surface treatment process is optimized to yield a low surface energy coating. Such a coating is used in preparing imprint templates for imprint lithography. Treated templates have desirable release characteristics relative to untreated templates. Untreated template surfaces possess surface free energies of about 65 dynes/cm or more. A treatment procedure disclosed herein yields a surface treatment layer that exhibits a high level of durability. Durability of the surface treatment layer allows a template to be used for numerous imprints without having to replace the surface treatment layer. The surface treatment layer, in some embodiments, reduces the surface free energy of the lower surface measured at 25° C. to less than about 40 dynes/cm, or in some cases, to less than about 20 dynes/cm. 
     A surface treatment layer, in one embodiment, is formed by the reaction product of an alkylsilane, a fluoroalkylsilane, or a fluoroalkyltrichlorosilane with water. This reaction forms a silinated coating layer on the surface of the patterned template. For example, a silinated surface treatment layer is formed from a reaction product of tridecafluoro-1,1,2,2-tetrahydrooctyl trichlorosilane with water. A surface treatment layer may be formed using either a liquid-phase process or a vapor-phase process. In a liquid-phase process, the substrate is immersed in a solution of precursor and solvent. In a vapor-phase process, a precursor is delivered via an inert carrier gas. It may be difficult to obtain a purely anhydrous solvent for use in a liquid-phase treatment. Water in the bulk phase during treatment may result in clump deposition, which will adversely affect the final quality or coverage of the coating. In an embodiment of a vapor-phase process, the template is placed in a vacuum chamber, after which the chamber is cycle-purged to remove excess water. Some adsorbed water, however, remains on the surface of the template. A small amount of water, however, is believed to be needed to initiate a surface reaction, which forms the coating. It is believed that the reaction may be described by the formula:
 
R—SiCl 3 +3H 2 O=&lt;R—Si(OH) 3 +3HCl
 
     To facilitate the reaction, the template is brought to a desired reaction temperature via a temperature-controlled chuck. The precursor is then fed into the reaction chamber for a prescribed time. Reaction parameters such as template temperature, precursor concentration, flow geometries, etc. are tailored to the specific precursor and template substrate combination. By controlling these conditions, the thickness of the surface treatment layer is controlled. The thickness of the surface treatment layer is kept at a minimal value to minimize the interference of the surface treatment layer with the feature size. In one embodiment, a monolayer of the surface treatment layer is formed. 
     Discontinuous Template 
     In an embodiment, there are at least two separate depths associated with the recesses on the lower surface of the template.  FIGS. 20A and 20B  depict top and cross-sectional views, respectively, of a patterned template with recesses having two depths. Referring to  FIGS. 20A and 20B , a template includes one or more patterning areas  401 . In such embodiments, a first relatively shallow depth is associated with the recesses in patterning areas  401  of the template, as depicted in  FIG. 20B . Patterning areas  401  include the area replicated during patterning of the template. Patterning areas  401  are positioned within a region defined by border  409  of the template. Border  409  is defined as the region that extends from an outer edge of any of the patterning areas to an edge  407  of the template. The border  409  has a depth that is substantially greater than the depth of the recesses in patterning areas  401 . The perimeter of the template is herein defined as the boundary between the patterning areas and border  409 . As depicted in  FIG. 20A  four patterning areas  401  are positioned within the area defined by the template. Patterning areas  401  are separated from edges  407  of the template by border  409 . The “perimeter” of the template is defined by edges  403   a ,  403   b,    403   c ,  403   d ,  403   e ,  403   f ,  403   g , and  403   h  of patterning areas  401 . 
     Patterning areas  401  may be separated from each other by channel regions  405 . Channel regions  405  are recesses that are positioned between patterning areas  401  that have a greater depth than the recesses of pattering areas  401 . As described below, both border  409  and channel regions  405  inhibit the flow of liquid between patterning regions  401  or beyond the perimeter of patterning areas  401 , respectively. 
     The design of the template is chosen based on the type of lithography process used. For example, a template for positive imprint lithography has a design that favors the formation of discontinuous films on the substrate. In one embodiment, a template  12  is formed such that the depth of one or more structures is relatively large compared to the depth of structures used to form the patterning region, as depicted in  FIG. 15 . During use, template  12  is placed in a desired spaced relationship to substrate  20 . In such an embodiment, the gap (h 1 ) between the lower surface  536  of template  12  and substrate  20  is much smaller than the gap (h 2 ) between recessed surface  534  and substrate  20 . For example, h 1  may be less than about 200 nm, while h 2  may be greater than about 10,000 nm. When template  12  is brought into contact with curable liquid  40  on substrate  20 , curable liquid  40  leaves the region under recessed surface  534  and fills the gap between lower surface  536  and substrate  20 , as depicted in  FIG. 16 . It is believed that combinations of surface energies and capillary forces draw curable liquid  40  from the larger recess into the narrower region. As h 1  is decreased, forces applied to curable liquid  40  by template  12  may overcome capillary forces drawing curable liquid  40  under lower surface  536 . These forces may cause spreading of curable liquid  40  into the area under recessed surface  534 . The minimum value of h 1  at which curable liquid  40  is inhibited from spreading into a recess  532  is referred to herein as the “minimum film thickness.” Additionally, as h 1  increases, the capillary forces are reduced, eventually allowing curable liquid  40  to spread into the deeper recessed regions. The maximum value of h 1  at which the capillary forces are sufficient to inhibit flow of curable liquid  40  into the deeper recessed region is herein known as the “maximum film thickness.” 
     As depicted in  FIGS. 17 and 18 , in various embodiments, template  12  is formed such that a curable liquid placed on substrate  20  is inhibited from flowing beyond perimeter  412  of template  12 . In the embodiment depicted in  FIG. 17 , height h 1  is measured from substrate  20  to shallow recessed surface  552 . Shallow recessed surface  552  extends to the perimeter of template  12 . Thus, the edge of the template forms the height h 2  and is effectively infinite in comparison to height h 1 . In the embodiment depicted in  FIG. 18 , a deep recess is formed at the outer edge of template  12 . Height h 2  is measured between substrate  20  and deep recessed surface  554 . Height h 1  is again measured between substrate  20  and shallow recessed surface  552 . In either embodiment, height h 2  is much larger than height h 1 . If h 1  is small enough, the activating light curable liquid remains in the gap between template  12  and substrate  20  while a curing agent is applied. Deeply recessed portions are particularly useful for liquid confinement in step and repeat processes as described herein. 
     In an embodiment, template  12  and substrate  20  each have one or more alignment marks. Alignment marks may be used to align template  12  and substrate  20 . For example, one or more optical imaging devices (e.g., microscopes, cameras, imaging arrays, etc.) are used to determine alignment of the alignment marks. 
     In some embodiments, an alignment mark on the template may be substantially transparent to activating light. Alternatively, the alignment mark may be substantially opaque to alignment mark detection light. As used herein, alignment mark detection light and light used for other measurement and analysis purposes is referred to as “analyzing light.” In an embodiment, analyzing light includes, but is not limited to, visible light and/or infrared light. The alignment mark may be formed of a material different than the material of the body. For example, the alignment mark may be formed from SiO x  where x is about 1.5. In another example, the alignment mark may be formed of molybdenum silicide. Alternately, the alignment mark may include a plurality of lines etched on a surface of the body. The lines are configured to substantially diffuse activating light, but produce an analyzable mark under analyzing light. 
     In various embodiments, one or more deep recesses as described above may project entirely through the body of the template to form openings in the template. An advantage of such openings is that they may effectively ensure that height h 2  is very large with respect to h 1  at each opening. Additionally, in some embodiments, pressurized gas or vacuum may be applied to the openings. Pressurized gas or vacuum may also be applied to one or more openings after curing the liquid. For example, pressurized gas may be applied after curing as part of a peel and pull process to assist in separating the template from the cured liquid. 
     Alternate System Embodiments 
     The above described imprint lithography system  3900  may be modified according to alternate embodiments discussed below. It should be understood that any of the described alternative embodiments may be combined, singly or in combination, with any other system described herein. 
     As described above, imprint head  3100  includes fine orientation system  3111  that allows for a “passive” orientation of patterned template  3700  with respect to the substrate. In another embodiment, fine orientation system 3111 may include actuators  3134   a ,  3134   b  and  3134   c  coupled to flexure arms  3172 ,  3174 ,  3202  and  3204 . Actuators  3134   a ,  3134   b  and  3134   c  may allow “active” control of fine orientation system  3111 . During use an operator or a programmable controller monitors the orientation of patterned template  3700  with respect to the substrate. The operators or a programmable controller then alters the orientation of patterned template  3700  with respect to the substrate by operating actuators  3134   a ,  3134   b  and  3134   c . Movement of actuators  3134   a ,  3134   b  and  3134   c  causes motion of flexure arms  3172 ,  3174 ,  3202  and  3204  to alter the orientation of patterned template  3700 . In this manner an “active” control of fine positioning of the template with respect to the substrate may be achieved. An active fine orientation system  3111  is further described in U.S. Ser. No. 09/920,341 filed Aug. 1, 2001 (published as U.S. Publication No. 2002-0093122) entitled “Methods for High-Precision Gap Orientation Sensing Between a Transparent Template and Substrate for Imprint Lithography,” which is incorporated herein by reference. 
     In an alternate embodiment, imprint head  3100  may include pre-calibration system  3109 , as described above. Pre-calibration system  3109  includes flexure ring  3124  as depicted in  FIG. 21 . In place of fine orientation system  3100  as described above, template support system  3125  is coupled to pre-calibration ring. In contrast to fine orientation system  3100 , template support system  3125  is formed of substantially rigid and non-compliant members  3127 . These members provide a substantially rigid support for patterned template  3700  disposed in template support  3130 . In this embodiment, fine orientation may be achieved using motion stage  3600  instead of template support  3130 . 
     In previous embodiments, imprint head  3100  is coupled to the body in a fixed position. In an alternate embodiment, imprint head  3100  may be mounted to a motion system that allows imprint head  3100  to be moved along the X-Y plane, as depicted in  FIG. 22 . Imprint head  3100  is configured to support patterned template  3700  as described in any of the embodiments herein. Imprint head  3100  is coupled to a motion system that includes an imprint head chuck  3110  and imprint motion stage  3123 . Imprint head  3100  is mounted to imprint head chuck  3110 . Imprint head chuck  3110  interacts with imprint motion stage  3123  to move imprint head  3100  along an X-Y plane. Mechanical or electromagnetic motion systems may be used. Electromagnetic systems rely on the use of magnets to produce an X-Y planar motion in imprint chuck  3110 . Generally, an electromagnetic system incorporates permanent and electromagnetic magnets into imprint motion stage  3123  and imprint head chuck  3110 . The attractive forces of these magnets is overcome by a cushion of air between imprint head chuck  3110  and imprint head motion stage  3123  such that an “air bearing” is produced. Imprint head chuck  3110 , and therefore imprint head  3100 , is moved along an X-Y plane on a cushion of air. Electromagnetic X-Y motion stages are described in further detail in U.S. Pat. No. 6,389,702 entitled “Method and Apparatus for Motion Control,” which is incorporated herein by reference. In a mechanical motion system, imprint head chuck  3110  is attached to imprint motion stage  3123 . Imprint motion stage  3123  is then moved by use of various mechanical means to alter the position of imprint head chuck  3110 , and thus imprint head  3110 , along the X-Y plane. In this embodiment, imprint head  3100  may include a passive compliant fine orientation system, an actuated fine orientation system, or a rigid template support system, as described herein. 
     With imprint head  3100  coupled to a moving support, the substrate may be mounted to a stationary support. Thus, in an alternate embodiment, imprint head  3100  is coupled to an X-Y axis motion stage as described herein. A substrate is mounted to a substantially stationary substrate support. Stationary substrate support  3640  is depicted in  FIG. 40 . Stationary substrate support  3640  includes a base  3642  and a substrate chuck  3644 . Substrate chuck  3644  is configured to support a substrate during imprint lithography processes. Substrate chuck  3644  may employ any suitable means to retain a substrate to substrate chuck  3644 . In one embodiment, substrate chuck  3644  may include a vacuum system which applies a vacuum to the substrate to couple the substrate to substrate chuck  3644 . Substrate chuck  3644  is coupled to base  3642 . Base  3642  is coupled to motion stage support  3920  of imprint lithography system  3900  (see  FIG. 1 ). During use, stationary substrate support  3640  remains in a fixed position on motion stage support  3920  while the imprint head  3100  position is varied to access different portions of the substrate. 
     Coupling an imprint head to a motion stage can offer advantages over techniques in which the substrate is on a motion stage. Motion stages generally rely on an air bearing to allow substantially frictionless motion of motion stage  3600 . Generally, motion stages are not designed to accommodate significant pressure applied along the Z-axis. When pressure is applied to a motion stage chuck along the Z-axis, the motion stage chuck position will change slightly in response to this pressure. During a step and repeat process, a template that has a smaller area than the area of the substrate is used to form multiple imprinted areas. The substrate motion stage is relatively large compared to the template to accommodate the larger substrates. When a template contacts the substrate motion stage in a position that is off-center, the motion stage will tilt to accommodate the increased pressure. This tilt is compensated for by tilting the imprint head to ensure proper alignment. If, however, the imprint head is coupled to the motion stage, all of the forces along the Z-axis will be centered on the template, regardless of where on the substrate the imprinting is taking place. This leads to increased ease in alignment and may also increase the throughput of the system. 
     In an embodiment, a substrate tilt module  3654  may be formed in substrate support  3650 , as depicted in  FIG. 39 . Substrate support  3650  includes a substrate chuck  3652 , coupled to a substrate tilt module  3654  (see also  FIG. 38 ). Substrate tilt module  3654  is coupled to a base  3656 . Base  3656 , in one embodiment, is coupled to a motion stage which allows X-Y motion of substrate support  3650 . Alternatively, base  3656  is coupled to a support (e.g.,  3920 ) such that substrate support  3650  is mounted to imprint lithography system  3900  in a fixed position. 
     Substrate chuck  3652  may employ any suitable means to retain a substrate to substrate chuck  3652 . In one embodiment, substrate chuck  3652  may include a vacuum system which applies a vacuum to the substrate to couple the substrate to substrate chuck  3652 . Substrate tilt module  3654  includes a flexure ring  3658  coupled to flexure ring support  3660 . A plurality of actuators  3662  are coupled to flexure ring  3658  and flexure ring support  3660 . Actuators  3662  are operated to alter the tilt of flexure ring  3658 . Actuators  3662 , in one embodiment, use a differential gear mechanism that may be manually or automatically operated. In an alternate embodiment, actuators  3662  use an eccentric roller mechanism. An eccentric roller mechanism generally provides more vertical stiffness to substrate support  3650  than a differential gear system. In one embodiment, substrate tilt module  3654  has a stiffness that will inhibit tilt of the substrate when the template applies a force of between about 1 lb. to about 10 lbs. to a liquid disposed on the substrate. Specifically, substrate tilt module  3654  is configured to allow no more than 5 micro radians of tilt when pressure up to about 10 lbs. is applied to the substrate through the liquid on the template. 
     During use sensors coupled to substrate chuck  3652  may be used to determine the tilt of the substrate. The tilt of the substrate is adjusted by actuators  3662 . In this manner tilt correction of the substrate may be achieved. 
     Substrate tilt module  3654  may also include a fine orientation system. A substrate support that includes a fine orientation system  3111  is depicted in  FIG. 38 . To achieve fine orientation control, flexure ring  3658  includes a central recess in which substrate chuck  3652  is disposed. The depth of the central recess is such that an upper surface of a substrate disposed on substrate chuck  3652  is substantially even with an upper surface of flexure ring  3658 . Fine orientation may be achieved using actuators  3662 . Fine orientation is achieved by the use of actuators capable of controlled motion in the nanometer range. Alternatively, fine orientation may be achieved in a passive manner. Actuators  3662  may be substantially compliant. The compliance of actuators  3662  may allow the substrate to self-correct for variations in tilt when a template is in contact with a liquid disposed on a substrate surface. By disposing the substrate in a position that is substantially even with flexure ring  3658 , fine orientation may be achieved at the substrate-liquid interface during use. Compliance of actuators  3662  is thus transferred to the upper surface of the substrate to allow fine orientation of the substrate. 
     The above-described systems are generally configured to systems in which an activating light curable liquid is dispensed onto a substrate and the substrate and template are brought into proximity to each other. It should be understood, however, that the above-described systems may be modified to allow an activating light curable liquid to be applied to a template rather than the substrate. In such an embodiment, the template is placed below the substrate.  FIG. 41  depicts a schematic drawing of an embodiment of a system  4100  that is configured such that the template is positioned below a substrate. System  4100  includes an imprint head  4110  and a substrate support  4120  positioned above imprint head  4110 . Imprint head  4110  is configured to hold patterned template  3700 . Imprint head  4110  may have a similar design to any of the herein described imprint heads. For example, imprint head  4110  may include a fine orientation system  3111  as described herein. Imprint head  4110  may be coupled to an imprint head  4130 . Imprint head  4110  may be coupled in a fixed position and remain substantially motionless during use. Alternatively, imprint head  4110  may be placed on a motion stage that allows X-Y planar motion of imprint head  4110  during use. 
     The substrate to be imprinted is mounted onto a substrate support  4120 . Substrate support  4120  has a similar design to any of the herein described substrate supports. For example, substrate support  4120  may include a fine orientation system  3111  as described herein. Substrate support  4120  may be coupled to a support  4140  in a fixed position and remain substantially motionless during use. Alternatively, substrate support  4120  may be placed on a motion stage that allows X-Y planar motion of substrate support during use. 
     During use an activating light curable liquid is placed on patterned template  3700  disposed in imprint head  4110 . The template may be patterned or planar, depending on the type of operation to be performed. Patterned templates may be configured for use in positive, negative, or combinations of positive and negative imprint lithography systems as described herein. 
     Imprint Lithography Process 
     Negative Imprint Lithography Process 
     A typical imprint lithography process is shown in  FIGS. 23A-23F . As depicted in  FIG. 23A , template  12  is positioned in a spaced relation to substrate  20  such that a gap is formed between template  12  and substrate  20 . Template  12  may include a surface that defines one or more desired features, which may be transferred to substrate  20  during patterning. As used herein, a “feature size” generally refers to a width, length and/or depth of one of the desired features. In various embodiments, the desired features may be defined on the surface of template  12  as recesses and or a conductive pattern formed on a surface of template  12 . Surface  14  of template  12  may be treated with a thin surface treatment layer  13  that lowers template  12  surface energy and assists in separation of template  12  from substrate  20 . Surface treatment layers for templates are described herein. 
     In an embodiment, curable liquid  40  may be dispensed upon substrate  20  prior to moving template  12  into a desired position relative to substrate  20 . Curable liquid  40  may be a curable liquid that conforms to the shape of desired features of template  12 . In an embodiment, curable liquid  40  is a low viscosity liquid that at least partially fills the space of gap  31  without the use of high temperatures, as depicted in  FIG. 24A . Low viscosity liquids may also allow gap  31  between template  12  and substrate  20  to be closed without requiring high pressures. As used herein, the term “low viscosity liquids” refer to liquids having a viscosity of less than about 30 centipoise measured at about 25° C. Further details regarding appropriate selections for curable liquid  40  are discussed below. Template  12  may interact with curable liquid  40  to conform the liquid into a desire shape. For example, curable liquid  40  may conform to the shape of template  12  as depicted in  FIG. 23B . The position of template  12  may be adjusted to create a desired gap distance between template  12  and substrate  20 . The position of template  12  may also be adjusted to properly align template  12  with substrate  20 . 
     After template  12  is properly positioned, curable liquid  40  is cured to form a masking layer  42  on substrate  20 . In an embodiment, curable liquid  40  is cured using activating light  32  to form masking layer  42 . Application of activating light  32  through template  12  to cure the liquid is depicted, as shown in  FIG. 23C . After curable liquid  40  is substantially cured, template  12  is removed from masking layer  42 , leaving the cured masking layer  42  on the surface of substrate  20 , as depicted in  FIG. 23D . Masking layer  42  has a pattern that is complementary to the pattern of template  12 . Masking layer  42  may include a “base layer” (also called a “residual layer”) between one or more desired features. The separation of template  12  from masking layer  42  is done so that desired features remain intact without shearing or tearing from the surface of substrate  20 . Further details regarding separation of template  12  from substrate  20  following imprinting are discussed below. 
     Masking layer  42  may be used in a variety of ways. For example, in some embodiments, masking layer  42  may be a functional layer. In such embodiments, curable liquid  40  may be curable to form a conductive layer, a semiconductive layer, a dielectric layer and/or a layer having a desired mechanical or optical property. In another embodiment, masking layer  42  may be used to cover portions of substrate  20  during further processing of substrate  20 . For example, masking layer  42  may be used during a material deposition process to inhibit deposition of the material on certain portions of the substrate. Similarly, masking layer  42  may be used as a mask for etching substrate  20 . To simplify further discussion of masking layer  42 , only its use as a mask for an etching process will be discussed in embodiments described below. However, it is recognized that masking layers in embodiments described herein may be used in a variety of processes as previously described. 
     For use in an etch process, masking layer  42  may be etched using an etch process until portions of substrate  20  are exposed through masking layer  42 , as depicted in  FIG. 23E . That is, portions of the base layer may be etched away. Portions  44  of masking layer  42  may remain on substrate  20  for use in inhibiting etching of portions of substrate  20 . After etching of masking layer  42  is complete, substrate  20  may be etched using known etching processes. Portions of substrate  20  disposed under portions  44  of masking layer  42  may remain substantially unetched while the exposed portions of substrate  20  are etched. In this manner, a pattern corresponding to the pattern of template  12  may be transferred to substrate  20 . The remaining portions  44  of masking layer  42  may be removed leaving a patterned substrate  20 , depicted in  FIG. 23F . 
       FIGS. 24A-24D  illustrate an embodiment of an imprint lithography process using a transfer layer. A transfer layer  18  may be formed upon an upper surface of substrate  20 . Transfer layer  18  may be formed from a material that has different etch characteristics than underlying substrate  20  and/or masking layer  42  formed from curable liquid  40 . That is, each layer (e.g., transfer layer  18 , masking layer  42  and/or substrate  20 ) may be etched at least somewhat selectively with respect to the other layers. 
     Masking layer  42  is formed on the surface of transfer layer  18  by depositing a curable liquid on the surface of transfer layer  18  and curing masking layer  42 , depicted in  FIGS. 23A-23C . Masking layer  42  may be used as a mask for etching transfer layer  18 . Masking layer  42  is etched using an etch process until portions of transfer layer  18  are exposed through masking layer  42 , as depicted in  FIG. 24B . Portions  44  of masking layer  42  remain on transfer layer  18  and may be used to inhibit etching of portions of transfer layer  18 . After etching of masking layer  42  is complete, transfer layer  18  may be etched using known etching processes. Portions of transfer layer  18  disposed under portions  44  of masking layer  42  may remain substantially unetched while the exposed portions of transfer layer  18  are etched. In this manner, the pattern of masking layer  42  is replicated in transfer layer  18 . 
     In  FIG. 24C , portions  44  and etched portions of transfer layer  18  together form a masking stack  46  that may be used to inhibit etching of portions  44  of underlying substrate  20 . Etching of substrate  20  may be performed using a known etch process (e.g., a plasma etching process, a reactive ion etching process, etc.). As depicted in  FIG. 24D , masking stack  46  may inhibit etching of the underlying portions of substrate  20 . Etching of the exposed portions of substrate  20  may be continued until a predetermined depth is reached. An advantage of using masking stack  46  as a mask for etching of substrate  20  is that the combined stack of layers may create a high aspect ratio mask (i.e., a mask that has a greater height than width). A high aspect ratio masking layer may be desirable during the etching process to inhibit undercutting of mask portions  44 . 
     The processes depicted in  FIGS. 23A-23F  and  FIGS. 24A-24D  are examples of negative imprint lithography processes. As used herein a “negative imprint lithography” process generally refers to a process in which the curable liquid is substantially conformed to the shape of the template before curing. That is, a negative image of the template is formed in the cured liquid. As depicted in these figures, the non-recessed portions of the template become the recessed portions of the mask layer. The template, therefore, is designed to have a pattern that represents a negative image of the pattern to be imparted to the mask layer. 
     Positive Imprint Lithography 
     As used herein a “positive imprint lithography” process generally refers to a process in which the pattern formed in the mask layer is a mirror image of the pattern of the template. As will be further described below, the non-recessed portions of the template become the non-recessed portions of the mask layer. 
     A typical positive imprint lithography process is shown in  FIGS. 25A-25D . As depicted in  FIG. 25A , template  12  is positioned in a spaced relation to substrate  20  such that a gap is formed between template  12  and substrate  20 . Surface of template  12  may be treated with a thin surface treatment layer  13  that lowers template  12  surface energy and assists in separation of template  12  from cured masking layer  42 . 
     Curable liquid  40  is disposed on the surface of substrate  20 . Template  12  is brought into contact with curable liquid  40 . As depicted in  FIG. 25B , the curable liquid fills the gap between the lower surface of template  12  and substrate  20 . In contrast to a negative imprint lithography process, curable liquid  40  is substantially absent from regions of substrate  20  approximately below at least a portion of the recesses of template  12 . Thus, curable liquid  40  is maintained as a discontinuous film on substrate  20  that is defined by the location of at least a portion of the recesses of template  12 . After template  12  is properly positioned, curable liquid  40  is cured to form masking layer  42  on substrate  20 . Template  12  is removed from masking layer  42 , leaving cured masking layer  42  on the surface of substrate  20 , as depicted in  FIG. 25C . Masking layer  42  has a pattern that is complementary to the pattern of template  12 . 
     Masking layer  42  may be used to inhibit etching of portions of substrate  20 . After formation of masking layer  42  is complete, substrate  20  may be etched using known etching processes. Portions of substrate  20  disposed under masking layer  42  may remain substantially unetched while the exposed portions of substrate  20  are etched, as depicted in  FIG. 25D . In this manner, the pattern of template  12  may be replicated in substrate  20 . The remaining portions  44  of masking layer  42  may be removed to create patterned substrate  20 . 
       FIGS. 26A-26C  illustrate an embodiment of a positive imprint lithography process using transfer layer  18 . Transfer layer  18  may be formed upon an upper surface of a substrate  20 . Transfer layer  18  is formed from a material that has different etch characteristics than the underlying transfer layer  18  and/or substrate  20 . A masking layer  42  is formed on the surface of transfer layer  18  by depositing a curable liquid on the surface of transfer layer  18  and curing the masking layer as depicted in  FIGS. 25A-25C . 
     Masking layer  42  may be used as a mask for etching transfer layer  18 . Masking layer  42  may inhibit etching of portions of transfer layer  18 . Transfer layer  18  may be etched using known etching processes. Portions of transfer layer  18 , disposed under masking layer  42 , may remain substantially unetched while the exposed portions of transfer layer  18  are etched. In this manner, the pattern of masking layer  42  may be replicated in transfer layer  18 . 
     In  FIG. 26B , masking layer  42  and etched portions of transfer layer  18  together form masking stack  46  that may be used to inhibit etching of portions of the underlying substrate  20 . Etching of substrate  20  may be performed using known etching processes (e.g., a plasma etching process, a reactive ion etching process, etc.). As depicted in  FIG. 26C , the masking stack may inhibit etching of the underlying portions of substrate  20 . Etching of the exposed portions of substrate  20  may be continued until a predetermined depth is reached. 
     Positive/Negative Imprint Lithography 
     In an embodiment, a process may combine positive and negative imprint lithography. A template for a combined positive and negative imprint lithography process may include recesses suitable for positive lithography and recesses suitable for negative lithography. For example, an embodiment of a template for combined positive and negative imprint lithography is depicted in  FIG. 27A . Template  12 , as depicted in  FIG. 27A , includes a lower surface  566 , at least one first recess  562 , and at least one second recess  564 . First recess  562  is configured to create a discontinuous portion of curable liquid  40  when template  12  contacts curable liquid  40 . A height of first recess (h 2 ) is substantially greater than a height of second recess (h 1 ). 
     A typical combined imprint lithography process is shown in  FIGS. 27A-27D . As depicted in  FIG. 27A , template  12  is positioned in a spaced relation to substrate  20  such that a gap is formed between template  12  and substrate  20 . At least lower surface  566  of template  12  may be treated with a thin surface treatment layer (not shown) that lowers template  12  surface energy and assists in separation of template  12  from cured masking layer  42 . Additionally, surfaces of first recesses  562  and/or second recesses  564  may be treated with the thin surface treatment layer. 
     Curable liquid  40  is disposed on the surface of substrate  20 . Template  12  is brought into contact with curable liquid  40 . As depicted in  FIG. 27B , curable liquid  40  fills the gap between the lower surface  566  of template  12  and substrate  20 . Curable liquid  40  also fills first recesses  562 . However, curable liquid  40  is substantially absent from regions of substrate  20  approximately below second recesses  564 . Thus, curable liquid  40  is maintained as a discontinuous film on substrate  20  that includes surface topography corresponding to the pattern formed by first recesses  562 . After template  12  is properly positioned, curable liquid  40  is cured to form a masking layer  42  on substrate  20 . Template  12  is removed from masking layer  42 , leaving cured masking layer  42  on the surface of substrate  20 , as depicted in  FIG. 27C . Masking layer  42  may include a patterned region  568  that resembles a mask layer formed by negative imprint lithography. In addition, masking layer  42  may include a channel region  569  that does not include any masking material. 
     In one embodiment, masking layer  42  is composed of a material that has the same or a similar etch rate as underlying substrate  20 . An etch process is applied to masking layer  42  to remove masking layer  42  and substrate  20  at substantially the same etch rate. In this manner the multilayer pattern of template  12  may be transferred to substrate  20 , as depicted in  FIG. 27D . This process may also be performed using a transfer layer  18  as described in other embodiments. 
     A combination of positive and negative lithography is also useful for patterning multiple regions of template  12 . For example, substrate  20  may include a plurality of regions that require patterning. As depicted in  FIG. 27C , template  12  with multiple depth recesses includes two patterning regions  568  with an intervening “channel” region  569 . Channel region  569  inhibits flow of a liquid beyond the patterning area of template  12 . 
     Step and Repeat 
     As used herein, a “step and repeat” process refers to using a template smaller than the substrate to form a plurality of patterned regions on the substrate. A step and repeat imprint process includes depositing a light curable liquid on a portion of a substrate, aligning a pattern in the cured liquid to previous patterns on the substrate, impressing a template into the liquid, curing the liquid, and separating the template from the cured liquid. Separating the template from the substrate may leave an image of the topography of the template in the cured liquid. Since the template is smaller than the total surface area of the substrate, only a portion of the substrate includes the patterned cured liquid. The “repeat” portion of the process includes depositing a light curable liquid on a different portion of the substrate. A patterned template is then aligned with the substrate and contacted with curable liquid  40 . Curable liquid  40  is cured using activating light to form a second area of cured liquid. This process may be continually repeated until most of the substrate is patterned. Step and repeat processes may be used with positive, negative, or positive/negative imprint processes. Step and repeat processes may be performed with any embodiments of equipment described herein. 
     Step and repeat imprint lithography processes offer a number of advantages over other techniques. Step and repeat processes described herein are based on imprint lithography that uses low viscosity light curable liquids and rigid, transparent templates. The templates are transparent to liquid activating light and alignment mark detection light thus offering the potential for layer-to-layer alignment. For production-scale imprint lithography of multi-level devices, it is advantageous to possess very high-resolution layer-to-layer alignment (e.g., as low as ⅓ rd  of the minimum feature size (“MFS”)). 
     There are various sources of distortion errors in the making of the templates. Step and repeat processes are used so that only a portion of a substrate is processed during a given step. The size of the field processed during each step should be small enough to possess pattern distortions of less than ⅓ rd  the MFS. This necessitates step and repeat patterning in high-resolution imprint lithography. This is also the reason why most optical lithography tools are step and repeat systems. Also, as discussed before, a need for low CD variations and defect inspection/repair favors processing of small fields. 
     In order to keep process costs low, it is important for lithography equipment to possess sufficiently high throughput. Throughput requirements put a stringent limit on the patterning time allowed per field. Low viscosity liquids that are light curable are attractive from a throughput point of view. These liquids move much faster to properly fill the gap between the template and the substrate, and the lithography capability is pattern independent. The resulting low pressure, room temperature processing is suitable for high throughput, while retaining the benefits of layer-to-layer alignment. 
     While prior inventions have addressed patterning of low viscosity light curable liquids, they have not addressed this for a step and repeat process. In photolithography, as well as in hot embossing, a film is spin coated and hard baked onto the substrate prior to its patterning. If such an approach is used with low viscosity liquids, there are three major problems. Low viscosity liquids are difficult to spin coat since they tend to de-wet and cannot retain the form of a continuous film. Also, in a step and repeat process, the liquid undergoes evaporation, thereby causing varying amounts of liquid to be left behind on the substrate as the template steps and repeats over the substrate. Finally, a blanket light exposure tends to disperse beyond the specific field being patterned. This tends to cause partial curing of the subsequent field, thereby affecting the fluid properties of the liquid prior to imprinting. An approach that dispenses liquid suitable for a single field onto the substrate, one field at a time, may solve the above three problems. However, it is important to accurately confine the liquid to that particular field to avoid loss of usable area on the substrate. 
     In general, lithography is one of many unit processes used in the production of devices. The cost of all of these processes, particularly in multi-layer devices, makes it highly desirable to place patterned regions as close as possible to each other without interfering with subsequent patterns. This effectively maximizes the usable area and hence the usage of the substrate. Also, imprint lithography may be used in a “mix-and-match” mode with other kinds of lithography, such as optical lithography, wherein different levels of the same device are made from different lithography technologies. It is advantageous to make the imprint lithography process compatible with other lithography techniques. A “kerf” region separates two adjacent fields on a substrate. In state-of-the-art optical lithography tools this kerf region may be as small as 50-100 microns. The size of the kerf is typically limited by the size of the blades used to separate the patterned regions. This small kerf region is expected to get smaller as the dicing blades that dice the individual chips get thinner. In order to accommodate this stringent kerf size requirement, the location of any excess liquid that is expelled from the patterned area should be well confined and repeatable. As such, the individual components, including the template, substrate, liquid and any other materials that affect the physical properties of the system, including but not limited to surface energy, interfacial energies, Hamacker constants, Van der Waals&#39; forces, viscosity, density, opacity, etc., are engineered as described herein to properly accommodate a repeatable process. 
     Formation of Discontinuous Films 
     As discussed previously, discontinuous films are formed using an appropriately patterned template. For example, a template with high aspect ratio recesses that define a border region can inhibit the flow of a liquid beyond the border area. The inhibition of the liquid within a border area is influenced by a number of factors. As discussed above template design plays a role in the confinement of a liquid. Additionally, the process by which the template is contacted with the liquid also influences the confinement of the liquid. 
       FIGS. 19A-19C  depict a cross-sectional view of a process wherein discontinuous films are formed on a surface. In one embodiment, curable liquid  40  is dispensed onto substrate  20  as a pattern of lines or droplets, as depicted in  FIG. 19A . Curable liquid  40 , therefore, does not cover an entire area of substrate  20  to be imprinted. As lower surface  536  of template  12  contacts curable liquid  40 , the force of template  12  on curable liquid  40  causes curable liquid  40  to spread over the surface of substrate  20 , as depicted in  FIG. 19B . Generally, the more force that is applied by template  12  to curable liquid  40 , the further curable liquid  40  will spread over substrate  20 . Thus, if a sufficient amount of force is applied, curable liquid  40  may be forced beyond a perimeter of template  12 , as depicted in  FIG. 19C . By controlling the forces applied to curable liquid  40  by template  12 , curable liquid  40  is confined within the predetermined borders of template  12 , as depicted in  FIG. 19D . 
     The amount of force applied to curable liquid  40  is related to the amount of liquid dispensed on substrate  20  and the distance template  12  is from substrate  20  during curing. For a negative imprint lithography process the amount of fluid dispensed onto the substrate should be less than or equal to a volume defined by: the volume of liquid required to substantially fill the recesses of the patterned template, the area of the substrate to be patterned, and the desired thickness of the cured layer. If the amount of cured liquid exceeds this volume, the liquid will be displaced from the perimeter of the template when the template is brought to the appropriate distance from the substrate. For a positive imprint lithography process the amount of liquid dispensed onto the substrate should be less than the volume defined by: the desired thickness of the cured layer (i.e., the distance between the non-recessed portions of the template and the substrate) and the surface area of the portion of the substrate to be patterned. 
     For an imprint lithography processes that uses a template that includes a border, the distance between the non-recessed surface of the template and the substrate is set between the minimum film thickness and the maximum film thickness, as previously described. Setting the height between these values allows the appropriate capillary forces to contain the liquid within the border-defined areas of the template. Additionally, the thickness of the layer should be approximately comparable to the height of the patterned features. If the cured layer is too thick, the features formed in the cured layer may be eroded before the features can be transferred to the underlying substrate. It is therefore desirable to control the volume as described above to allow the appropriate film thickness to be used. 
     The force applied by template  12  to curable liquid  40  is also influenced by the rate at which template  12  is brought into contact with curable liquid  40 . Generally, the faster template  12  is brought into contact, the more force is applied to curable liquid  40 . Thus, some measure of control of the spread of curable liquid  40  on the surface of substrate  20  may be achieved by controlling the rate at which template  12  is brought into contact with curable liquid  40 . 
     All of these features are considered when positioning template  12  with respect to substrate  20  for an imprint lithography process. By controlling these variables in a predetermined manner, the flow of curable liquid  40  may be controlled to stay confined within a predetermined area. 
     Alignment Techniques 
     Overlay alignment schemes include measurement of alignment errors followed by compensation of these errors to achieve accurate alignment of a patterned template and a desired imprint location on a substrate. Correct placement of the template with respect to the substrate is important for achieving proper alignment of the patterned layer with any previously formed layers on the substrate. Placement error, as used herein, generally refers to X-Y positioning errors between a template and substrate (that is, translation along the X- and/or Y-axis). Placement errors, in one embodiment, are determined and corrected for by using a through the template optical device, as depicted in  FIG. 14 . 
       FIG. 28  illustrates a schematic diagram of optical system  3820  through the template optical imaging system  3800  (see also  FIG. 14 ). Optical system  3820  is configured to focus two alignment marks from different planes onto a single focal plane. Optical system  3820  may use the change of focal length resulting from light with distinct wavelengths to determine the alignment of the template with an underlying substrate. Optical system  3820  may include optical imaging device  3810 , an illumination source (not shown), and a focusing device  3805 . Light with distinct wavelengths may be generated either by using individual light sources or by using a single broad band light source and inserting optical band-pass filters between the imaging plane and the alignment marks. Depending on the gap between patterned template  3700  and substrate  2500 , different wavelengths are selected to adjust the focal lengths. Under each wavelength of light used, each overlay mark may produce two images on the imaging plane, as depicted in  FIG. 29 . A first image  2601 , using a specific wavelength of light, is a clearly focused image. A second image  2602 , using the same wavelength of light, is an out-of-focus image. In order to eliminate each out-of-focus image, several methods may be used. 
     In a first method, under illumination with a first wavelength of light, two images may be received by optical imaging device  3810 . Images are depicted in  FIG. 29  and generally referenced by numeral  2604 . While images are depicted as squares, it should be understood that any other shape might be used, including crosses. Image  2602  corresponds to an overlay alignment mark on the substrate. Image  2601  corresponds to an overlay alignment mark on the template. When image  2602  is focused, image  2601  is out of focus. In an embodiment, an image processing technique may be used to erase geometric data corresponding to pixels associated with image  2602 . Thus, the out-of-focus image of the substrate mark may be eliminated, leaving only image  2601 . Using the same procedure and a second wavelength of light, images  2605  and  2606  may be formed on optical imaging device  3810 . The out-of-focus image  2606  is then eliminated, leaving only image  2605 . The two remaining focused images  2601  and  2605  are then combined onto a single imaging plane  2603  for making overlay error measurements. 
     A second method may utilize two coplanar polarizing arrays, as depicted in  FIG. 30 , and polarized illumination sources.  FIG. 30  illustrates overlay marks  2701  and orthogonally polarizing arrays  2702 . Polarizing arrays  2702  are formed on the template surface or placed above the surface. Under two polarized illumination sources, only focused images  2703  (each corresponding to a distinct wavelength and polarization) may appear on the imaging plane. Thus, out-of-focus images are filtered out by polarizing arrays  2702 . An advantage of this method may be that it may not require an image processing technique to eliminate out-focused images. 
     Moiré pattern based overlay measurement has been used for optical lithography processes. For imprint lithography processes, where two layers of Moiré patterns are not on the same plane but still overlapped in the imaging array, acquiring two individual focused images may be difficult to achieve. However, carefully controlling the gap between the template and substrate within the depth of focus of the optical measurement tool and without direct contact between the template and substrate may allow two layers of Moiré patterns to be simultaneously acquired with minimal focusing problems. It is believed that other standard overlay schemes based on the Moiré patterns may be directly implemented to imprint lithography process. 
     Another concern with overlay alignment for imprint lithography processes that use UV curable liquid materials may be the visibility of the alignment marks. For the overlay placement error measurement, two overlay marks, one on the template and the other on substrate are used. However, since it is desirable for the template to be transparent to a curing agent, the template overlay marks, in some embodiments, are not opaque lines. Rather, the template overlay marks are topographical features of the template surface. In some embodiment, the marks are made of the same material as the template. In addition, UV curable liquids may have a refractive index that is similar to the refractive index of the template materials (e.g., quartz). Therefore, when the UV curable liquid fills the gap between the template and the substrate, template overlay marks may become very difficult to recognize. If the template overlay marks are made with an opaque material (e.g., chromium), the UV curable liquid below the overlay marks may not be properly exposed to the UV light. 
     In an embodiment, overlay marks are used on the template that are seen by optical imaging system  3800  but are opaque to the curing light (e.g., UV light). An embodiment of this approach is illustrated in  FIG. 31 . In  FIG. 31 , instead of completely opaque lines, overlay marks  3102  on the template may be formed of fine polarizing lines  3101 . For example, suitable fine polarizing lines have a width about ½ to ¼ of the wavelength of activating light used as the curing agent. The line width of polarizing lines  3101  should be small enough so that activating light passing between two lines is diffracted sufficiently to cause curing of all the liquid below the lines. In such an embodiment, the activating light may be polarized according to the polarization of overlay marks  3102 . Polarizing the activating light provides a relatively uniform exposure to all the template regions including regions having overlay marks  3102 . Light used to locate overlay marks  3102  on the template may be broadband light or a specific wavelength that may not cure the liquid material. This light need not be polarized. Polarizing lines  3101  are substantially opaque to the measuring light, thus making overlay marks  3102  visible using established overlay error measuring tools. Fine polarized overlay marks are fabricated on the template using existing techniques, such as electron beam lithography. 
     In another embodiment, overlay marks  3102  are formed of a different material than the template. For example, a material selected to form the template overlay marks  3102  may be substantially opaque to visible light, but transparent to activating light used as the curing agent (e.g., UV light). For example, SiO x  where X is less than 2, may be used as such a material. In particular, structures formed of SiO x , where X is about 1.5, are substantially opaque to visible light, but transparent to UV curing light. 
     Liquid Dispensing Patterns 
     In all embodiments of an imprint lithography process, a liquid is dispensed onto a substrate. While the following description is directed to dispensing liquids on substrate, it should be understood that the same liquid dispensing techniques are also used when dispensing liquids onto a template. Liquid dispensing is a carefully controlled process. In general, liquid dispensing is controlled such that a predetermined amount of liquid is dispensed in the proper location on the substrate. Additionally, the volume of liquid is also controlled. The combination of the proper volume of liquid and the proper location of the liquid is controlled by using the liquid dispensing systems described herein. Step and repeat processes, in particular, use a combination of liquid volume control and liquid placement to confine patterning to a specified field. 
     A variety of liquid dispensing patterns are used. Patterns may be in the form of continuous lines or patterns of droplets of liquid. In some embodiments, relative motion between a displacement based liquid dispenser tip and an imprinting member is used to form a pattern with substantially continuous lines on a portion of the imprinting member. Balancing rates of dispensing and relative motion is used to control the size of the cross-section of the line and the shape of the line. During the dispensing process, the dispenser tips are fixed near (e.g., on the order of tens of microns) to the substrate. Two examples of continuous patterns are depicted in  FIGS. 32A and 32B . The pattern depicted in  FIGS. 32A and 32B  is a sinusoidal pattern; however, other patterns are possible. As depicted in  FIGS. 32A and 32B , a continuous line pattern may be drawn using either a single dispenser tip  2401  or multiple dispenser tips  2402 . Alternatively, a pattern of droplets may be used, as depicted in  FIG. 32C . In one embodiment, a pattern of droplets that has a central droplet that has a greater volume than surrounding droplets is used. When the template contacts the droplets, the liquid spreads to fill the patterning area of the template, depicted in  FIG. 32C . 
     Dispensing rate, V d , and relative lateral velocity of an imprinting member, v 5 , may be related as follows
 
 v   d   =V   d   /t   d (dispensing volume/dispensing period),  (1)
 
 v   s   =L/t   d (line length/dispensing period),  (2)
 
v d =a L(where, ‘a’ is the cross section area of line pattern),  (3)
 
     Therefore,
 
v d =a V s   (4)
 
     The width of the initial line pattern may normally depend on the tip size of a dispenser. The dispenser tip may be fixed. In an embodiment, a liquid dispensing controller is used to control the volume of liquid dispensed (V d ) and the time taken to dispense the liquid (t d ). If V d  and t d  are fixed, increasing the length of the line leads to lower height of the cross-section of the line patterned. Increasing pattern length may be achieved by increasing the spatial frequency of the periodic patterns. Lower height of the pattern may lead to a decrease in the amount of liquid to be displaced during imprint processes. By using multiple tips connected to the same dispensing line, line patterns with long lengths may be formed faster as compared to the case of a single dispenser tip. Alternatively, a plurality of closely spaced drops is used to form a line with an accurate volume. 
     Separation of Template 
     After curing of the liquid is completed, the template is separated from the cured liquid. Since the template and substrate are almost perfectly parallel, the assembly of the template, imprinted layer, and substrate leads to a substantially uniform contact between the template and the cured liquid. Such a system may require a large separation force to separate the template from the cured liquid. In the case of a flexible template or substrate, the separation, in one embodiment, is performed using a “peeling process.” However, use of a flexible template or substrate may be undesirable for high-resolution overlay alignment. In the case of a quartz template and a silicon substrate, a peeling process may be difficult to implement. In one embodiment, a “peel and pull” process is performed to separate the template from an imprinted layer. An embodiment of a peel and pull process is illustrated in  FIGS. 33A-33C . 
       FIG. 33A  depicts a template  12  embedded in curable liquid  40 . After curing of curable liquid  40 , either the template  12  or substrate  20  may be tilted to intentionally induce an angle  3604  between template  12  and substrate  20 , as depicted in  FIG. 33B . A pre-calibration stage, either coupled to template  12  or substrate  20  may be used to induce a tilt between template  12  and curable liquid  40 . The relative lateral motion between template  12  and substrate  20  may be insignificant during the tilting motion if the tilting axis is located close to the template  12 -substrate  20  interface. Once angle  3604  between template  12  and substrate  20  is large enough, template  12  may be separated from substrate  20  using only Z-axis motion (i.e., vertical motion). This peel and pull method may result in desired portions  44  being left intact on a transfer layer  18  and substrate  20  without undesirable shearing. 
     Electrostatic Curing Process 
     In addition to the above-described embodiments, embodiments described herein include forming patterned structures by using electric fields. Cured layers formed using electric fields to induce a pattern in the cured layer may be used for single imprinting or step and repeat processes. 
       FIG. 34  depicts an embodiment of template  1200  and substrate  1202 . Template  1200 , in one embodiment, is formed from a material that is transparent to activating light to allow curing of the polymerizable composition by exposure to activating light. Forming template  1200  from a transparent material also allows the use of established optical techniques to measure the gap between template  1200  and substrate  1202  and to measure overlay marks to perform overlay alignment and magnification correction during formation of the structures. Template  1200  is also thermally and mechanically stable to provide nano-resolution patterning capability. Template  1200  includes an electrically conducting material and/or layer  1204  to allow electric fields to be generated at template-substrate interface. 
     In one embodiment, a blank of fused silica (e.g., quartz) is used as the material for base  1206  of template  1200 . Indium tin oxide (ITO) is deposited onto base  1206 . ITO is transparent to visible and UV light and is a conducting material. ITO may be patterned using high-resolution electron beam lithography. A low-surface energy coating, as previously described, may be coated onto template  1200  to improve the release characteristics between template  1200  and the polymerized composition. Substrate  1202  may include standard wafer materials, such as Si, GaAs, SiGeC and InP. A UV curable liquid and/or a thermally curable liquid may be used as polymerizable composition  1208 . In an embodiment, polymerizable composition  1208  may be spin coated onto wafer  1210 . In another embodiment, a predetermined volume of polymerizable composition  1208  may be dispensed onto substrate  1202  in a predetermined pattern, as described herein. In some embodiments, transfer layer  1212  may be placed between wafer  1210  and polymerizable composition  1208 . Transfer layer  1212  material properties and thickness may be chosen to allow for the creation of high-aspect ratio structures from low-aspect ratio structures created in the cured liquid material. Connecting ITO to a voltage source  1214  may generate an electric field between template  1200  and substrate  1202 . 
     In  FIGS. 35A-35D  and  FIGS. 36A-36C , two embodiments of the above-described process are illustrated. In each embodiment, a desired uniform gap may be maintained between template  1200  and substrate  1202 . An electric field of the desired magnitude may be applied resulting in the attraction of polymerizable composition  1208  towards the raised portions  1216  of template  1200 . 
     In  FIGS. 35A-35D , the gap and field magnitudes are such that polymerizable composition  1208  makes direct contact and adheres to template  1200 . A curing agent (e.g., activating light  1218  and/or heat) may be used to cure the liquid. Once desired structures have been formed, template  1200  may be separated from substrate  1202  by methods described herein. 
     In  FIGS. 36A-36C , the gap and field magnitudes may be chosen such that polymerizable composition  1208  achieves a topography that is essentially the same as that of template  1200 . This topography may be achieved without making direct contact with template  1200 . A curing agent (e.g., activating light  1218 ) may be used to cure the liquid. In the embodiment of  FIGS. 35A-35D  and  FIGS. 36A-36C , a subsequent etch process may be used to remove the cured material  1220 . A further etch may also be used if transfer layer  1212  is present between cured material  1220  and wafer  1210 , as depicted in  FIGS. 35A-35D  and  FIGS. 36A-36C . 
     In another embodiment,  FIG. 37A  depicts an electrically conductive template that includes a continuous layer of electrically conductive portions  1504  coupled to a non-conductive bases  1502 . As shown in  FIG. 37B  the non-conductive bases  1502  of the template are isolated from each other by the conductive portions  1504 . The template may be used in a “positive” imprint process, as described above. 
     In an embodiment, an “adjustable” template may be used to form a pattern on a substrate. The term “adjustable” template, in the context of this embodiment, generally refers to a template that includes electrically conductive portions that are independently controlled. Controlling a conductive portion of the template refers to turning on, turning off, and/or adjusting an electric field of the conductive portion. This concept is illustrated in  FIG. 42 . Template  1700  includes electrically conductive portions  1702  and non-conductive material  1704 . Non-conductive material  1704  insulates conductive portions  1702  from each other. Template  1700  is substantially transparent to some or all types of activating light. In an embodiment, template  1700  is formed from materials that are thermally stable. Conductive portions  1702  may be formed from, for example, ITO. Non-conductive material  1704  may be formed from, for example, silicon dioxide. Conductive portions  1702  form a pattern complementary to a pattern to be produced on a masking layer. The pattern of conductive portions  1702  is formed in nonconducting material  1704  using methods known to those skilled in the art. Conductive portions  1702  are to be electrically connected  1706  to power source  1708 , either independently or together. In an embodiment where the conductive portions  1702  are independently connected to power source  1708 , there may be a control device  1710  to independently adjust the electric field generated by one or more conductive portions  1702 . In an embodiment, electrical connectors  1712  run through non-conductive material  1704  from another side to connect to conductive portions  1702 . In an alternate embodiment, conductive portions  1702  extend through nonconductive material  1704  such that electrical connectors  1712  are not required. 
     Such embodiments may create lithographic patterned structures quickly (in a time of less than about 1 second). The structures generally have sizes on the order of tens of nanometers. In one embodiment, curing a polymerizable composition in the presence of electric fields creates a patterned layer on a substrate. The pattern is created by placing a template with specific nanometer-scale topography at a controlled distance (e.g., within nanometers) from the surface of a thin layer of the curable liquid on a substrate. If all or a portion of the desired structures are regularly repeating patterns, such as an array of dots, the pattern on the template may be considerably larger than the size of the desired repeating structures. 
     The replication of the pattern on the template may be achieved by applying an electric field between the template and the substrate. Because the liquid and air (or vacuum) have different dielectric constants and the electric field varies locally due to the presence of the topography of the template, an electrostatic force may be generated that attracts regions of the liquid toward the template. Surface tension or capillary pressures tend to stabilize the film. At high electric field strengths, the polymerizable composition may be made to attach to the template and de-wet from the substrate at certain points. However, the attachment of the liquid film will occur provided the ratio of electrostatic forces is comparable to the capillary forces, which are measured by the dimensionless number Λ. The magnitude of the electrostatic force is approximately εE 2 d 2 , where ε is the permittivity of vacuum, E is the magnitude of the electric field, and d is the feature size. The magnitude of the capillary forces is approximately γd, where γ is the liquid-gas surface tension. The ratio of these two forces is 
             Λ   =         ɛ   ⁢           ⁢     E   2     ⁢   d     γ     .           
In order to deform the interface and cause it to attach to the upper surface, the electric field must be such that L is approximately unity. The precise value depends on the details of the topography of the plates and the ratio of liquid-gas permittivities and heights, but this number will be 0(1). Thus, the electric field is approximately given by
 
             E   ∼         (     γ     ɛ   ⁢           ⁢   d       )       1   2       .           
This polymerizable composition may be hardened in place by polymerization of the composition. The template may be treated with a low energy self-assembled monolayer film (e.g., a fluorinated surfactant) to aid in detachment of the template from the polymerized composition.
 
     An example of the above approximations is given below. For d=100 nm and γ=30 mJ/m, and ε=8.85×10−12 C 2 /J−m, E=1.8×10 8  V/m, which corresponds to a potential difference between the plates of 18 V if the plate spacing is 100 nm or 180 V if the plate spacing is 1000 nm. Note that the feature size 
               d   ∼     γ     ɛ   ⁢           ⁢     E   2           ,         
which means that the size of the feature decreases with the square of the electric field. Thus, 50 nm features would require voltages on the order of 25 or 250 V for 100 and 1000 nm plate spacings, respectively.
 
     It may be possible to control the electric field, the design of the topography of the template, and the proximity of the template to the liquid surface so as to create a pattern in the polymerizable composition that does not come into contact with the surface of the template. This technique may eliminate the need for mechanical separation of the template from the polymerized composition. This technique may also eliminate a potential source of defects in the pattern. In the absence of contact, however, the liquid may not form sharp, high-resolution structures that are as well defined, as in the case of contact. This may be addressed by first creating structures in the polymerizable composition that are partially defined at a given electric field. Subsequently, the gap may be increased between the template and substrate while simultaneously increasing the magnitude of the electric field to “draw-out” the liquid to form clearly defined structures without requiring contact. 
     The polymerizable composition may be deposited on top of a transfer layer as previously described. Such a bi-layer process allows low aspect ratio, high-resolution structures formed using electrical fields to be followed by an etch process to yield high-aspect ratio, high-resolution structures. Such a bi-layer process may also be used to perform a “metal lift-off process” to deposit a metal on the substrate such that the metal is left behind after lift-off in the trench areas of the originally created structures. 
     Using a low viscosity polymerizable composition, pattern formation using electric fields may be fast (e.g., less than about 1 sec.), and the structure may be rapidly cured. Avoiding temperature variations in the substrate and the polymerizable composition may also avoid undesirable pattern distortion that makes nano-resolution layer-to-layer alignment impractical. In addition, as mentioned above, it is possible to quickly form a pattern without contact with the template, thus eliminating defects associated with imprint methods that require direct contact. 
     In this patent, certain U.S. patents, and U.S. patent applications have been incorporated by reference. The text of such U.S. patents, and U.S. patent applications is, however, only incorporated by reference to the extent that no conflict exists between such text and the other statements and drawings set forth herein. In the event of such conflict, U.S. patents, and U.S. patent applications are specifically not incorporated by reference in this patent. 
     While this invention has been described with references to various illustrative embodiments, the description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.