Patent Publication Number: US-2022229361-A1

Title: Roll-to-roll nanoimprint lithography tools and processes

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 62/847,193 entitled “Nanoscale Replication And Registration Using Roll-To-Roll Template With Precision Alignment,” filed on May 13, 2019 and U.S. Provisional Patent Application Ser. No. 62/847,690, entitled “Roll-To-Roll Nanofabrication Process For Flexible Cu Metal Mesh Transparent Conducting Electrodes,” filed on May 14, 2019, which are incorporated by reference herein in their entirety. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to UV-based nanoimprint lithography, and more particularly to configuring UV-based nanoimprint lithography for roll-to-roll (R2R) processing and a roll-to-roll nanofabrication process for metal mesh transparent conducting electrodes. 
     BACKGROUND 
     Nanoimprint lithography (NIL) is a method of fabricating nanometer scale patterns. It is a simple nanolithography process with low cost, high throughput and high resolution. It creates patterns by mechanical deformation of imprint resist and subsequent processes. The imprint resist is typically a monomer or polymer formulation that is cured by heat or ultraviolet (UV) light during the imprinting (UV-based nanoimprint lithography). Adhesion between the resist and the template is controlled to allow proper release. 
     UV-based nanoimprint lithography (UV-NIL) offers a variety of advantages in the replication of patterns, both uniform and non-uniform, such as by providing precise nanoscale patterning. 
     In the field of electronic devices, roll-to-roll processing, also known as web processing, reel-to-reel processing or R2R, is the process of creating electronic devices on a roll of flexible plastic or metal foil. In other fields predating this use, it can refer to any process of applying coatings, printing, or performing other processes starting with a roll of a flexible material and re-reeling after the process to create an output roll. These processes, and others, such as sheeting, can be grouped together under the general term converting. When the rolls of material have been coated, laminated or printed they can be subsequently slit to their finished size on a slitter rewinder. 
     While R2R processing is an inexpensive process, it has not been able to be utilized using precise nanoscale patterning afforded by UV-NIL. 
     Furthermore, current technologies for realizing optoelectronic devices, such as metal mesh transparent conducting electrodes, wire grid polarizers and light-trapping gratings, are limited to rigid substrates, lack the necessary patterning resolution, involve inefficient metal lift-off/etch process and/or a transfer printing step. 
     SUMMARY 
     In one embodiment of the present invention, a plate-to-roll nanoimprint lithography process for creating a roll-based high volume manufacturing template by patterning nanoscale features using a rigid template with nanoscale patterns on to a substrate held in a roll-to-roll configuration, the process comprises coating a film of a solution of resist material on the template. The process further comprises performing in-situ alignment of the template with the substrate. The process additionally comprises initiating a substantially point or line contact between the substrate and the template. Furthermore, the process comprises exercising control over an out-of-plane deflection profile of the substrate or the template. Additionally, the process comprises crosslinking the resist material with UV light while the out-of-plane deflection profile of the substrate matches a surface profile of a top surface of the template. In addition, the process comprises separating the template from the substrate through manipulation of motion of the template or the substrate. 
     In another embodiment of the present invention, a roll-to-plate nanoimprint lithography process by patterning nanoscale features using a roll-based high volume manufacturing (RHVM) template with nanoscale patterns held in a roll-to-roll configuration on to a substrate, the process comprises coating a film of a solution of nanoimprint resist material on the substrate. The process further comprises performing in-situ alignment of the substrate with the template. The process additionally comprises initiating a substantially point or line contact between the template and the substrate. Furthermore, the process comprises exercising control over an out-of-plane deflection profile of the template or the substrate. Additionally, the process comprises crosslinking the resist material with UV light while the out-of-plane deflection profile of the template matches a surface profile of a top surface of the substrate. In addition, the process comprises separating the template from the substrate through manipulation of motion of the template or the substrate. 
     In a further embodiment of the present invention, a roll-to-roll nanoimprint lithography process by patterning nanoscale features using a roll-based high volume manufacturing (RHVM) template with nanoscale patterns held in a roll-to-roll (R2R) configuration on to a substrate held in a roll-to-roll configuration, the process comprises driving the template and the substrate to be incoming at substantially a same speed and tension. The process further comprises coating a film of a solution of nanoimprint resist material on the substrate. The process additionally comprises performing an in-situ alignment of the substrate with the template. Furthermore, the process comprises initiating a substantially point or line contact between the incoming template and the incoming substrate. Additionally, the process comprises exercising control over an out-of-plane deflection profile of the substrate or the template. In addition, the process comprises crosslinking the resist material with UV light while the out-of-plane deflection profile of the template matches a surface profile of a top surface of the substrate. The process further comprises separating the template from the substrate through manipulation of the substrate or the template. 
     In another embodiment of the present invention, a method for nano-precise edge-stitching of large-area templates comprises providing a master template that contains embedded alignment marks along with optical patterns to be imprinted. The method further comprises providing a large-area substrate, which is to be tessellated with master template imprints, that contains embedded alignment marks. The method additionally comprises performing error sensing by measuring a relative displacement between pairs of embedded alignment marks on the master template and the large-area substrate. 
     In a further embodiment of the present invention, a method for selective electroless copper (Cu) metallization comprises depositing a protection layer on a substrate. The method further comprises depositing a palladium seed layer on the protection layer. The method additionally comprises dispensing a polymeric adhesion promoting layer on the palladium seed layer. Furthermore, the method comprises curing the polymeric adhesion promoting layer. Additionally, the method comprises transferring trench patterns on to a surface of the cured polymeric adhesion promoting layer forming a sample. In addition, the method comprises exposing the sample to a linear ion source in order to etch a residual layer thickness of an imprint resist layer. The method further comprises immersing the sample in a plating solution to metallize trenches of the trench patterns and form an interconnect embedded metal mesh electrode. 
     In another embodiment of the present invention, a nanoimprint lithography apparatus comprises fixtures for mounting coating systems. The apparatus further comprises an ultraviolet (UV) transparent area. The apparatus additionally comprises a module for control of an out-of-plane deflection profile of a template or a substrate. Furthermore, the apparatus comprises a stage for mounting the template which allows in-plane and out-of-plane motion of the template or a stage for mounting the substrate which allows in-plane and out-of-plane motion of the substrate. Additionally, the apparatus comprises a module for the substrate or the template held in a roll-to-roll configuration configured to ensure a substantially flat zone for imprinting. In addition, the apparatus comprises an evaporation module for evaporating resist material from the template or the substrate. 
     The foregoing has outlined rather generally the features and technical advantages of one or more embodiments of the present invention in order that the detailed description of the present invention that follows may be better understood. Additional features and advantages of the present invention will be described hereinafter which may form the subject of the claims of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the present invention can be obtained when the following detailed description is considered in conjunction with the following drawings, in which: 
         FIG. 1  is a schematic view of the Roll-to-Plate (R2P) NIL tool (also used as Plate-to-Roll (P2R) NIL tool) in accordance with an embodiment of the present invention; 
         FIG. 2  is a schematic view of the web path in the R2P tool with the nip rollers configuration in accordance with an embodiment of the present invention; 
         FIG. 3  is a schematic view of the web path in the R2P tool with the vacuum rollers configuration in accordance with an embodiment of the present invention; 
         FIG. 4  is a schematic view of the web path in the R2R NIL tool with nip rollers and independent drivers in accordance with an embodiment of the present invention; 
         FIG. 5  is a schematic view of the web path in the R2R tool with vacuum rollers and independent drivers for the substrate and template web in accordance with an embodiment of the present invention; 
         FIG. 6  is a schematic view of the web path in the R2R tool with nip rollers and a single driver for the substrate and template web in accordance with an embodiment of the present invention; 
         FIG. 7  is a schematic view of the web path in the R2R tool with vacuum rollers and a single driver for the substrate and template web in accordance with an embodiment of the present invention; 
         FIGS. 8A-8C  illustrate the architecture of the sidelay mechanism in accordance with an embodiment of the present invention; 
         FIGS. 9A-9B  illustrate the roll template tension control system in accordance with an embodiment of the present invention; 
         FIG. 10A  illustrates the precision alignment system of idlers in the imprint zone in accordance with an embodiment of the present invention; 
         FIG. 10B  illustrates the side view of the precision alignment system when the vacuum is off, the bearing air pressure is off, the cavity air pressure is off and the precision alignment system is in the dormant mode in accordance with an embodiment of the present invention; 
         FIG. 10C  illustrates the side view of the precision alignment system when the vacuum is on, the bearing air pressure is on, the cavity air pressure is on and the precision alignment system is in the conveying mode in the R2R configuration in accordance with an embodiment of the present invention; 
         FIGS. 11A-11C  illustrates the components of the UV transparent vacuum preloaded air bearing in accordance with an embodiment of the present invention; 
         FIGS. 12A-12C  illustrate the vertical-tip-tilt motion stage in accordance with an embodiment of the present invention; 
         FIGS. 13A-13B  illustrate the at-line mechanism for template and substrate parallelism in accordance with an embodiment of the present invention; 
         FIG. 14  is a flowchart of a method of the process steps for R2P-NIL and R2R-NIL in the start-stop configuration in accordance with an embodiment of the present invention; 
         FIGS. 15A-15H  depict the cross-sectional views of the process steps for R2P-NIL and R2R-NIL in the start-stop configuration using the steps described in  FIG. 14  in accordance with an embodiment of the present invention; 
         FIG. 16  is a flowchart of a method of the process steps in the continuous R2R-NIL configuration in accordance with an embodiment of the present invention; 
         FIGS. 17A-17H  depict the cross-sectional views of the process steps in the continuous R2R-NIL configuration using the steps described in  FIG. 16  in accordance with an embodiment of the present invention; 
         FIGS. 18A-18C  illustrate an ink-jet assembly and fixture for large width ink-jetting in accordance with an embodiment of the present invention; 
         FIG. 19  is a schematic view of the use of inkjets in conjunction with slot-die coating to obtain non-uniform film profiles as required for non-uniform nano-patterning in accordance with an embodiment of the present invention; 
         FIG. 20  illustrates the tension and speed mismatch allowance in the template and substrate web to avoid shearing of nano-patterns in accordance with an embodiment of the present invention; 
         FIG. 21  is a schematic view of in-line metrology and DMD (digital micromirror device) based thermal actuation to control the resist thickness profile before entering the NIL module in accordance with an embodiment of the present invention; 
         FIG. 22  illustrates an in-line overlay sensing subsystem in accordance with an embodiment of the present invention; 
         FIG. 23  is a schematic view of the Moiré alignment marks on the template and the Moiré alignment marks on the substrate in accordance with an embodiment of the present invention; 
         FIG. 24  is a schematic view denoting a Moiré microscope apparatus suitable for embodiments with precise web handling in accordance with an embodiment of the present invention; 
         FIG. 25  is a schematic view denoting Moiré alignment marks with coarse alignment bars for embodiments without stringent web handling requirements in accordance with an embodiment of the present invention; 
         FIGS. 26A-26B  illustrate the at-line overlay metrology apparatus in accordance with an embodiment of the present invention; 
         FIG. 27  illustrates an automated mechanism for orientating idler rollers for the template web in accordance with an embodiment of the present invention; 
         FIG. 28  is a schematic view of vertical motion roll substrate stages for overlay correction due to rigid body motion errors in accordance with an embodiment of the present invention; 
         FIG. 29  illustrates a zoomed-in view of the 6 degree of the freedom flexure stage describing the compliant mechanisms deployed for overlay correction in accordance with an embodiment of the present invention; 
         FIG. 30  is a schematic of a substrate web accumulator for embodiments involving overlay correction in accordance with an embodiment of the present invention; 
         FIG. 31  is a schematic of a template composed of a 3×3 grid of imprinted patterns, showing various kinds of edge-stitching errors in accordance with an embodiment of the present invention; 
         FIG. 32  is a schematic of a large-area substrate to be tessellated with a 3×3 grid of master patterns with the first field in the process of being patterned in accordance with an embodiment of the present invention; 
         FIG. 33  is a schematic of a master template and a large-area substrate with a dense array of alignment marks in accordance with an embodiment of the present invention; 
         FIG. 34  illustrates an exemplar fabrication sequence for the master template in accordance with an embodiment of the present invention; 
         FIG. 35  illustrates an exemplar fabrication sequence for embedding alignment marks in the large area-substrate in accordance with an embodiment of the present invention; 
         FIG. 36  illustrates an exemplar sequence for edge-stitching in a non-rectilinear substrate (alignment) grid in accordance with an embodiment of the present invention; 
         FIG. 37  illustrates exemplar scenarios where edge-stitching could fail in accordance with an embodiment of the present invention; 
         FIG. 38  illustrates the motion configuration with the large-area X, Y stage on the substrate side and the theta (θ) stage on the template side in accordance with an embodiment of the present invention; 
         FIG. 39  illustrates an alternative embodiment for motion configuration with a gantry type X, Y stage on the template stage in accordance with an embodiment of the present invention; 
         FIG. 40  illustrates an exemplar configuration for the template and substrate-side thermal actuation in accordance with an embodiment of the present invention; 
         FIG. 41  illustrates an exemplar configuration for the substrate-side pinhole array to improve thermal conductivity in accordance with an embodiment of the present invention; 
         FIG. 42  is a flowchart of a method for selective electroless Cu (ECu) metallization in accordance with an embodiment of the present invention; 
         FIGS. 43A-43G  depict the cross-sectional views for selective ECu metallization using the steps described in  FIG. 42  in accordance with an embodiment of the present invention; 
         FIG. 44A  illustrates an image of patterned quartz (insert is of fields consisting of trench grids) in accordance of an embodiment of the present invention; 
         FIGS. 44B-44C  are scanning electron microscope (SEM) images of the fine grid pattern in accordance of an embodiment of the present invention; and 
         FIGS. 44D-44F  are SEM images of the coarse grid pattern after 60 seconds of ECu plating in accordance of an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     As stated in the Background section, UV-based nanoimprint lithography (UV-NIL) offers a variety of advantages in the replication of patterns, both uniform and non-uniform, such as by providing precise nanoscale patterning. 
     In the field of electronic devices, roll-to-roll processing, also known as web processing, reel-to-reel processing or R2R, is the process of creating electronic devices on a roll of flexible plastic or metal foil. In other fields predating this use, it can refer to any process of applying coatings, printing, or performing other processes starting with a roll of a flexible material and re-reeling after the process to create an output roll. These processes, and others, such as sheeting, can be grouped together under the general term converting. When the rolls of material have been coated, laminated or printed they can be subsequently slit to their finished size on a slitter rewinder. 
     While R2R processing is an inexpensive process, it has not been able to be utilized using precise nanoscale patterning afforded by UV-NIL. 
     The principles of the present invention provide the means for configuring UV-NIL for R2R processing, which combines the benefits of inexpensive R2R processing with the precise nanoscale patterning afforded by NIL as discussed herein. 
     Referring to the Figures in detail,  FIG. 1  is a schematic view of the Roll-to-Plate (R2P) NIL tool  100  (also used as a Plate-to-Roll (P2R) NIL tool) in accordance with an embodiment of the present invention.  FIG. 2  illustrates a schematic view of the web path in the R2P NIL tool  100  with the nip rollers configuration in accordance with an embodiment of the present invention. 
     Referring to  FIGS. 1 and 2  in combination, R2P NIL tool  100  uses a roll template to imprint on a rigid substrate  201 . Tool  100  includes a diameter sensor  101 , sidelay linear bearing  102 , tie beams  103 , sidelay actuator  104 , edge sensor  105 , machine feet  106 , granite slab  107 , base support  108 , space  109  for electronics, pneumatic controllers, etc., reel chuck assemblies  110 , load cell rollers  111 , capstan roller  112 , nip roller  113 , ultraviolet (UV) exposure lamp  114 , sidewalls  115 , coating assembly  116 , UV transparent chuck/conveyer  117 , substrate chuck/conveyer  118 , vertical-tip-tilt stage  119 , and linear stages  120 . 
     In one embodiment, a master template (e.g., a gen 2.5 glass with dimensions 400 mm×500 mm) can be used as a rigid template and to imprint upwards on a flexible roll substrate (e.g., a 500 mm wide web made of polycarbonate, PET, PEN, etc.). This process is called replication. The plate traversing system consists of three stages, a linear XY stage for slot-die coating using a slot-die coater  208  and ink jetting and a vertical, tip and tilt stage  119  to control parallelism and separation of the template from the substrate. A stage (see element  211 ) with a travel range of 100-10000 mm enables positioning and coating the plate using a slot-die coater  208  and in some embodiments, the inkjet. Vertical stage (see element  119 ) is driven by actuators, such as piezoelectric elements, and voice coil motors (VCMs) (driven by VCM stage  205  for vertical, tip and tilt motion). One embodiment of the stage provides a vertical displacement of 0.1-50 mm and an angular travel range of 0.1-5 degrees. Another embodiment of the stage provides an increased angular travel range of ˜5-30 degrees, albeit it occupies a larger space. Both the stages are mounted on a granite base  107  to dampen vibrations. The template web handling module consists of unwind and rewind rollers, rollers  202  for interleaving and de-interleaving, drive rollers  207 , nip rollers  113  for tension control and precision rollers to ensure a flat zone for imprinting. The sidelay module  203  ensures that the web is wound on each other without lateral error (telescoping). The template roll is unwound from a supply roller  206 , de-interleaved, and passed through a drive roller  207 . Drive roller  207  provides the necessary tension control in the imprinting region. Various embodiments of drive roller  207  are described later herein. Downstream of the imprinting region, the template web is interleaved (via interleaf roller  202 ) to prevent particle contamination and wound back on take-up roller  206 . In one embodiment, every roller in the system is mounted on manual alignment stages for accurate axial orientation. A broadband UV lamp  114  is used to cure imprint resist  209 . Imprint actuation is achieved using UV transparent vacuum chucks  117  (see also vacuum pin chuck  210  of  FIG. 2 ) with a central zone of positive air cavity pressure. In one embodiment, the material for components of UV transparent vacuum preloaded air bearings includes UV transmitting acrylic, quartz or cyclic olefin copolymer. 
       FIG. 2  shows the web path followed by the template web and the interleaf film during removal and application. Tension control is achieved through a nip and drive roller assembly (nip roller  113  and drive rollers  207 ). Polyurethane rollers are used to apply normal pressure on drive roller  207  which improves friction and allows higher tension limited by motor capacity. In one embodiment, nip roller  113  is axially parallel to drive roller  207 . In one embodiment, precision idlers  204  are used to flatten the roll. A UV lamp  114  is placed directly above the imprint zone. The UV transparent vacuum preloaded air bearing is positioned between the template and UV lamp  114 . Precision idlers  204  are shown which flatten the web and ensure minimal out of plane errors and in-plane shear errors. 
       FIG. 3  is a schematic view of the web path in R2P tool  100  with the vacuum rollers configuration in accordance with an embodiment of the present invention. 
     Referring to  FIG. 3 , a pair of vacuum rollers  301  are used to provide tension to the roll template in the imprinting region. In general, vacuum rollers  301  are useful when dealing with delicate webs or sparse pattern density. Vacuum rollers  301  provide tension without normal compressive force on the patterned side of the roll template. The normal force created by vacuum rollers  301  is sufficient for the desired tension range (˜10-5000 N/m). 
       FIG. 3  further illustrates UV transparent vacuum preloaded air bearing  302 . 
       FIG. 4  is a schematic view of the Roll-to-Roll (R2R) NIL tool with nip rollers and independent drivers for the substrate and template web in accordance with an embodiment of the present invention. 
     Referring to  FIG. 4 , the R2R NIL tool uses a roll template to imprint on a roll substrate in either a start-and-stop discrete manner or a continuous manner. The roll substrate  401  is unwound from a supply roller and de-interleaved. It is then passed through an optional web cleaning module (not shown) which removes particles on the web. In one embodiment, it is followed by a tensioned-web slot die coater  402  which deposits an imprint resist solution, where the thickness of the resist solution can be 50-10,000 nm. Any solvent in the resist can be evaporated using an oven or an infrared (IR) heater  403 . In one embodiment, the resist material is coated on the substrate using slot-die coating, tensioned-web slot-die coating, kiss gravure coating, micro-gravure coating, doctor blading, knife-edge coating, ink jetting or a combination thereof to control a film thickness profile of the resist material. 
     In one embodiment, a film of a solution of resist material is coated on the template. In one embodiment, a film of a solution of nanoimprint resist material is coated on the substrate. 
     Substrate web  401  then passes through the imprint zone  404  through a vacuum preloaded air bearing  405  used as a contactless conveyer, where it is actuated upon by UV transparent air bars and the template web  406  is brought in contact to it. Several embodiments of the drive and actuation processes are described below. After imprinting and separation, the patterned web  401  passes through a spectral imaging module  407  and scatterometry module  408  to characterize and quantify defects. Following metrology module  407  are the take-up roller  206  (see  FIGS. 2-3 ) and the interleaf roller  202  (see  FIGS. 2-3 ) along with an optional web cleaning module (not shown). 
     Referring to  FIG. 4 , a couple of nip rollers  113  are used to drive the web and provide tension control. In one embodiment, substrate web  401  and template web  406  have independent drivers. Speed and tension matching is also carried out in the imprinting region (imprint zone  404 ) 
       FIG. 5  is a schematic view of the web path in the R2R tool with vacuum rollers  301  (see  FIG. 3 ) and independent drivers for the substrate web  401  and the template web  406  in accordance with an embodiment of the present invention. 
     As shown in  FIG. 5 , a pair of vacuum rollers  301  is used to provide tension control. 
       FIG. 6  is a schematic view of the web path in the R2R tool with nip rollers  113  ( FIGS. 1-2 and 4 ) and a single driver for substrate and template web  401 ,  406  ( FIGS. 4-5 ) in accordance with an embodiment of the present invention. 
     Referring to  FIG. 6 , a single nip roller  113  downstream of the imprint region is used to drive both the substrate and template rollers  401 ,  406 . This prevents issues due to mismatching of speed and tension. The oncoming substrate and template web  401 ,  406  are made to contact each other along a single line through air bearings. The vertical tip tilt stage  119  ( FIG. 1 ) is used to mount the bottom vacuum preloaded air bearing and provide gap control and proper alignment. 
       FIG. 7  is a schematic view of the web path in the R2R tool with vacuum rollers  301  and a single driver for substrate and template web  401 ,  402  ( FIGS. 4 and 5 ) in accordance with an embodiment of the present invention. 
       FIGS. 8A-8C  illustrate the architecture of the sidelay module  203  ( FIGS. 2-7 ) in accordance with an embodiment of the present invention. Referring to  FIGS. 8A-8C ,  FIGS. 8A-8C  illustrate that sidelay module  203  is used to ensure that the web does not displace laterally due to accumulating errors (telescoping). The unwind roller  801 , de-interleaf roller  202 , load cell roller  111 , nip roller  113  and drive roller  207  are mounted on a carriage than can translate in a perpendicular direction to the web motion. An edge guide sensor  802  is used to locate the lateral position of the roll template along with limit switches to detect the end of the travel range. 
       FIGS. 8B-8C  further illustrate that linear bearings  803  transverse to the web motion, tie beams  804 , sidelay actuator  104  ( FIG. 1 ), sensors  805  for reel diameter measurement, and a linear motor moving sidelay module  806  transverse to the web with respect to the stationary frame  807 . 
       FIGS. 9A-9B  illustrate the roll template tension control system in accordance with an embodiment of the present invention. Referring to  FIGS. 9A-9B , the tension control is maintained using a nip roller  113  of the nip+drive roller  901  (nip+drive roller includes nip roller  113  and drive roller  207  of  FIG. 2 ) in the imprint module, and unwind and rewind rollers for overall web tension. Load cells  902 - 906  (load cell for unwind tension  902 , load cell for de-interleaf tension  903 , load cell for imprinting zone tension  904 , load cell for rewind tension  905  and load cell for interleaf tension  906 ) and diameter measurement sensors  907  are used to calculated tension in each region. These sensor inputs are fed to the motion controller driving the motors and appropriate tension control is achieved. 
       FIG. 10A  illustrates the precision alignment system  1000  of idlers in the imprint zone in accordance with an embodiment of the present invention. Referring to  FIG. 10A , mechanism  1000  includes a precision idler  204  mounted on self-aligning bearings  1001 . Self-aligning bearings  1001  are themselves mounted on 2-axis stages  1002  (e.g., XY stages) to ensure proper alignment of rollers. The 2-axis stages are located on the sidewalls through line boring. Laser tracking sensors can be used to measure misalignment between any 2 rollers in the system. 
       FIG. 10B  illustrates the side view of precision alignment system  1000  when the vacuum is off, the bearing air pressure is off, the cavity air pressure is off and precision alignment system  1000  is in the dormant mode in accordance with an embodiment of the present invention. In such a mode, micrometer knobs  1003  are mounted to the ball end  1004  glued to the micrometer actuator via micrometer mounts  1005 . As shown in  FIG. 10B , the ball ends  1004  are protected via a ball sleeve  1006 . Additionally, as shown in  FIG. 10B , in one embodiment, there may be a stationary plate  1007  to which micrometers are fastened. 
       FIG. 10C  illustrates the side view of precision alignment system  1000  when the vacuum is on, the bearing air pressure is on, the cavity air pressure is on and precision alignment system  1000  is in the conveying mode in the R2R configuration in accordance with an embodiment of the present invention. In such a mode, there exists an air cavity  1008  with a gap of less than 100 micrometers between template web  406  and UV transparent vacuum preloaded air bearing  302  ( FIG. 3 ) is maintained through the vacuum to sustain cavity pressure. 
       FIGS. 11A-11C  illustrates the components of the UV transparent vacuum preloaded air bearing  302  in accordance with an embodiment of the present invention. Referring to  FIGS. 11A-11C ,  FIGS. 11A-11C  illustrate that UV transparent vacuum preloaded air bearing assembly  302  consisting of 3 plates,  1101 ,  1102 ,  1103 . In one embodiment, the bottom plate  1101  (adjacent to substrate web  401 ) is made of porous ceramic to ensure vacuum chucking of the web with minimal dimples in stop-and-start applications. In continuous applications, vacuum and positive air pressure are both applied to convey the web. In one embodiment, the central zone is UV transparent. Furthermore, in one embodiment, metal plates  1102 ,  1103  in the middle and away from the web are used to route air and vacuum to the necessary areas of the web. In one embodiment, the three plate assembly sits on kinematic joints that can be manually aligned as needed. Capacitive sensors are incorporated on the edges of the air bearings for alignment correction. In one embodiment, the UV transparent region  1108  is drilled with holes and pathways  1109  to pump air onto the template web to create a curvature as shown in  FIG. 11C . This curvature is used to ensure substantially point or line contact with liquid resist on the substrate web. An array of cameras can be optionally mounted on top of the UVT (ultraviolet transmitting) chuck to observe formation of bubbles, if any. In case of any bubble entrapment, extra air can be targeted at the specific location using the pathways in the UV transparent chuck to mitigate the bubble. In one embodiment, image processing is used to detect bubbles and pneumatic controllers are automatically activated. A similar assembly is used below the substrate web in the conveyer/chuck mode. The substrate chuck assembly may not have a UV transparent part because the UV lamp is situated above the template. However, in some embodiments, this configuration may be reversed. 
       FIG. 11B  shows the substrate side of the vacuum preloaded air bearing  302  for two different modes. In one of the modes (left side), the vacuum is on, the air pressure is on and the mode is the conveying mode in the R2R configuration. In the other mode (right side), the vacuum is on, the air pressure is off and the mode is the chucking mode in the R2P configuration. 
       FIG. 11C  shows the side section view of vacuum preloaded air bearing  302 , which includes the UVT (ultraviolet transmitting) acrylic plate  1110  and the porous region  1111  with through holes  1109  on edges to the chuck/convey web as shown in the bottom view of UV transparent preloaded air bearing showing the UV transparent region.  FIG. 11C  further illustrates vacuum supply  1112  and bearing  1113  with positive pressure supply. 
       FIGS. 12A-12C  illustrate the vertical-tip-tilt motion stage  119  ( FIG. 1 ) in accordance with an embodiment of the present invention. 
     Referring to  FIGS. 12A-12C ,  FIGS. 12A-12C  describe the stage for vertical motion and tip and tilt alignment. Three actuators  1201  are mounted vertically on a base plate  1202  as shown in  FIG. 12A . The vertical motion of the actuators is defined by the compliant translational joints that are designed to increase range of motion while maintaining high stiffness. Limit switches and mechanical hard stops are added to sense the end of the travel range and avoid damage to the motors and bearings. 
     In particular,  FIG. 12A  illustrates a flexural universal bearing  1203  ( FIG. 12C  includes a detailed drawing of flexural universal bearing  1203 ) connected to base plate  1202  and translational flexure bearing  1204  ( FIG. 12B  includes a detailed drawing of translational flexure bearing  1204 ). In one embodiment, a displacement sensor  1205  is placed on translational flexure bearing  1204  connected to stationary chassis  1206 . Additionally, as shown in  FIG. 12A , each actuator  1201  includes a voice coil motor  1207 . 
       FIGS. 13A-13B  illustrate a precision alignment mechanism  1300  for plates and webs in accordance with an embodiment of the present invention. As shown in  FIG. 13A , mechanism  1300  includes a UV transparent chuck  117  with incorporated capacitance sensors. Mechanism  1300  further includes a roll template  1301  on precision idlers  204 , a pin chuck  1302  with incorporated capacitance sensors, and a VCM stage  1303  for vertical, tip and tilt motion. As shown in  FIG. 13B , metal  1304  is deposited on the edges of roll template  1301  to measure parallelism. 
     As shown in  FIG. 13A , mechanism  1300  is deployed to ensure parallelism between UV transparent chuck  1107 , the template web precision idlers  204  and the substrate chuck (or substrate air bearing). In one embodiment, vertical-tip-tilt motion stage  119  ( FIG. 1 ) is automatically controlled. In one embodiment, the vacuum chuck (not shown) mounted on vertical-tip-tilt motion stage  119  is incorporated with capacitive sensors. In one embodiment, UV transparent vacuum preloaded air bearing&#39;s pitch and roll angle is manually adjusted by mounting the air bearing on a kinematic joint. The metallic template web (or any material responsive to displacement measurement sensors) traverses through precision idlers  204  mounted on manual alignment stages. As a result, parallelism can be maintained between the three bodies with an accuracy of less than 0.1 radians. 
       FIGS. 14 and 15A-15H  illustrate the process steps involved in the R2P-NIL and R2R-NIL in the start-stop configuration.  FIG. 14  is a flowchart of a method  1400  of the process steps for R2P-NIL and R2R-NIL in the start-stop configuration in accordance with an embodiment of the present invention.  FIGS. 15A-15H  depict the cross-sectional views of the process steps for R2P-NIL and R2R-NIL in the start-stop configuration using the steps described in  FIG. 14  in accordance with an embodiment of the present invention. 
     Referring to  FIG. 14 , in conjunction with  FIGS. 15A-15H , in step  1401 , substrate  1501  is positioned via a substrate web guide for R2R as shown in  FIG. 15A . 
     In step  1402 , a slot-die coating of resist solution  1502  is performed as shown in  FIG. 15B . In one embodiment, a ˜10% resist solution  1502  is deposited on substrate  1501 . 
     In step  1403 , solvent evaporation is performed thereby exposing resist solution  1502  to IR radiation  1503  leaving a resist layer  1504  as shown in  FIG. 15C . In one embodiment, by IR drying, the 90% solvent evaporates leaving a 10-1000 nm resist layer  1504  (or 25 nm BT20 adhesive layer). 
     In step  1404 , the plate temperature is cooled to ambient conditions. 
     In step  1405 , template  1505  is bowed until contact is made with substrate  1501  as shown in  FIG. 15D . In one embodiment, roll template  1505  is bowed using the UV transparent vacuum preloaded air bearings  302  ( FIG. 3 ). In one embodiment, bowing is utilized for bubble mitigation. In one embodiment, web deflection is substantially higher than the flatness of the substrate to ensure single point or single line contact. 
     Once contact is made, capillary forces are allowed to take over and air bar pressure is increased in step  1406  to aid in capillary fill  1506  as shown in  FIG. 15E . 
     In step  1407 , air bar pressure is continued to be applied with UV flash  1507  as shown in  FIG. 15F . In one embodiment, a broadband UV lamp is used to cure resist  1504 . 
     In step  1408 , UV transparent vacuum preloaded air bearing cavity pressure is reduced to recreate the bow of template  1505  for controlled delamination as shown in  FIG. 15G . In one embodiment, template  1505  is bowed to ensure proper peeling in order to prevent pattern shear with template separation. The vertical-tip-tilt stage can also be used to aid the process of template separation. The UVT (ultraviolet transmitting) vacuum preloaded air bearing can also be used to maintain the web position by chucking the web along its edges. Cameras mounted on the top-side of the UV transparent vacuum preloaded air bearing  302  are used to observe bubble entrapment, if any. In one embodiment, the cavity air pressure used for bowing can be appropriately corrected to mitigate the bubble. 
     In step  1409 , inline spectral imaging and scatterometry  1508  are utilized to characterize and quantify defects as shown in  FIG. 15H . 
       FIGS. 16 and 17A-17H  illustrate the process steps involved in the continuous R2R-NIL configuration.  FIG. 16  is a flowchart of a method  1600  of the process steps in the continuous R2R-NIL configuration in accordance with an embodiment of the present invention.  FIGS. 17A-17H  depict the cross-sectional views of the process steps in the continuous R2R-NIL configuration using the steps described in  FIG. 16  in accordance with an embodiment of the present invention. 
     Referring to  FIG. 16 , in conjunction with  FIGS. 17A-17H , in step  1601 , substrate  1701  is positioned via a substrate web guide as shown in  FIG. 17A . In one embodiment, a web guide with a 1, 10, 100 or 1,000 micrometer accuracy is used to maintain roll alignment and prevent telescoping over the entire process. 
     In step  1602 , a slot-die coating of resist solution  1702  is performed as shown in  FIG. 17B . In one embodiment, a ˜10% resist solution  1702  is deposited on substrate  1701 . In one embodiment, slot-die coating is preceded with de-interleaving and web cleaning. 
     In step  1603 , solvent evaporation is performed thereby exposing resist solution  1702  to IR radiation  1703  leaving a resist layer  1704  as shown in  FIG. 17C . In one embodiment, by IR drying, the 90% solvent evaporates leaving a 10-1,000 nm resist layer  1804  (or 25 nm BT20 adhesive layer). 
     In step  1604 , the web temperature is cooled to bring the web temperature to ambient conditions. 
     In step  1605 , incoming template  1705  and substrate  1701  with resist layer  1704  are bowed to mitigate bubbles as shown in  FIG. 17D . In one embodiment, template  1705  and substrate  1701  are maintained at the same tension and are traversing at the same speed. The amount of speed and tension mismatch the patterns can handle without shearing is discussed further below. 
     As template  1705  and substrate  1701  approach the imprint area, the vacuum preloaded air bearings on the top and bottom induce a curvature by applying positive pressure. This curvature induces a line contact and mitigates bubbles. Downstream of the curvature zone, template  1705  and substrate  1701  are in complete contact which allows capillary fill  1706  in step  1606  as shown in  FIG. 17E . Cameras mounted on the top-side of UV transparent vacuum preloaded air bearing  302  ( FIG. 3 ) are used to observe bubble entrapment, if any. The positive air pressure can be appropriately corrected to mitigate the bubble 
     In step  1607 , UV flash  1707  is performed as shown in  FIG. 17F . 
     In step  1608 , template  1705  and substrate  1701  are separated without sheer via controlled delamination as shown in  FIG. 17G . For controlled separation, the curvature induced downstream of the imprinting zone leads to a single line separation and proper peeling. In one embodiment, it is ensured that the gap between the web and vacuum preloaded air bearing  302  is small enough (&lt;100 μm) by increasing the vacuum pressure at the edges. Due to this, curvature in the web due to cavity in the pressure is produced faster. 
     In step  1609 , inline spectral imaging and scatterometry  1708  are utilized to characterize and quantify defects as shown in  FIG. 17H . 
       FIGS. 18A-18C  illustrate an ink-jet assembly and fixture for large width ink-jetting in accordance with an embodiment of the present invention. Referring to  FIGS. 18A-18C ,  FIG. 18A  illustrates the top view  1801  and  FIG. 18B  illustrates the bottom view  1802  of the large width inkjet assembly.  FIG. 18C  further illustrates the compliant mechanism  1803  that includes the fixed body  1804 , compliant revolute joints  1805 , and manual actuators  1806 . 
     In one embodiment, inkjet drops are deposited uniformly with an accuracy of 1-200 micrometers over a large width (500 mm). In another embodiment, an inkjet head is mounted on a stage with compliant bearings allowing motion in Y and θ. Combining one or more such inkjet stages provides a fixture with the necessary degrees of freedoms and sufficient range of motions to dispense drops uniformly. 
       FIG. 19  is a schematic view of the use of inkjets in conjunction with slot-die coating to obtain non-uniform film profiles as required for non-uniform nano-patterning in accordance with an embodiment of the present invention. 
     As shown in  FIG. 19 , slot-die coater  1901  deposits a resist solution  1902  on substrate  1903 , where the solvent in resist solution  1902  is evaporated via IR heater  1904 . As also shown in  FIG. 19 , inkjet heads  1905  are used to deposit inkjet drops  1906  using inkjet fixture  1907 . 
     Inkjet deposition of resist on slot-die coated films allows local control of the film thickness for better residual layer control assuming there are systematic non-uniformities in the system. The inkjetting can be done prior to the patterning step, and after evaporation by dispensing a formulation of the resist without the solvent. The determination of locations and volumes of inkjetted drops on the slot-die coated films can be done based on the pattern information on the template as well as the measurement of film thickness on the substrate. 
     In general, the determination of the locations of inkjetted drops, and initial alignment and contact between the template and the substrate requires robust metrology of the incoming film as well as the outgoing pattern. This metrology needs to be in-situ and can be coupled automatically with process control with the machine in the loop or with the help of reduced-order, physical, statistical or empirical models of various unit steps in the process. Based on this metrology, the process can be adjusted to ensure that all tolerances are substantially met during the initial start-up phase during which it is expected that the metrology would be the rate-limiting step. Following this initial start-up, the system can be run with minimal metrology sampled intelligently across the process in a feedforward “blind” manner until there is an anomaly that is detected. 
     It has been reported that exceeding the coating window at higher traversing speeds in slot-die coating leads to bead breakup and air entrainment leading to non-uniform coating. Consequently, although average film thickness decreases, it also leads to ribbing, i.e., waviness along cross web direction. By modelling air flow into slot gap, an exact description of the film thickness variation would be predicted. In one embodiment, non-uniformities in film thickness due to ribbing is compensated by inkjet dispense through a feed forward control system. This method would be used to coat films with high throughput. The slot-die coater can also be equipped with a vacuum box near the upstream lip to stabilize the bead and prevent air entrainment in the slot. 
     In one embodiment, an ex-situ metrology setup to measure film thickness variation due to air entrainment involves an array of reflectometers (or a microscope). Once film thickness variation has been mapped, the inkjet dispenser is used to dispense resist drops on the substrate at locations of lower thicknesses. 
     A fluid-template interaction model is used to calculate the effect of capillary forces on a tensioned web, particularly to check if the web collapses under capillary forces. A quantified relation between applied tension and film thickness variation is also found. Based on the lubrication theory which characterize thin film flows, the following partial differential equations (PDEs) govern the physics of the fluid-web interaction. 
     
       
         
           
             
               
                 
                   ∂ 
                   h 
                 
                 
                   ∂ 
                   t 
                 
               
               = 
               
                 
                   ∂ 
                   
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                 ⁢ 
                 
                   { 
                   
                     
                       
                         h 
                         s 
                         2 
                       
                       
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     where h 1 =resist film thickness, h 2 =gap of the template web from the substrate web in the region not containing resist, P f =fluid pressure, P a =pressure from air bearings, T 0 =applied web tension. A solution is assumed of the below format. 
     
       
         
           
             
               
                 h 
                 1 
               
               = 
               
                 
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                         A 
                         i 
                       
                       ⁡ 
                       
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                         t 
                         ) 
                       
                     
                     ⁢ 
                     
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                       ⁡ 
                       
                         ( 
                         
                           
                             l 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
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                             ⁢ 
                             
                                 
                             
                             ⁢ 
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     Using continuity, differentiability and capillary pressure difference boundary conditions at the fluid-air interface and symmetry elsewhere, the equations can be solved numerically. 
       FIG. 20  illustrates the tension and speed mismatch allowance in the template and substrate web to avoid shearing of nano-patterns in accordance with an embodiment of the present invention. 
     Process control in slot-die coating can be done by monitoring the bead location and liquid pressure. Pressure below a threshold leads to air entrainment leading to defects. Bead contact with the lips of the slot-die also indicates onset of air entrainment. 
     Reflectometers can be used to measure the imprint resist film thickness along a width. Any anomaly in film thickness can be used as a sensor to trigger changes in flow conditions. 
     The following equation describes wet film thickness in Tensioned Web Over Slot Die (TWOSD). T (tension), coating speed (V), and Pac (exit pressure) can be adjusted on the fly to minimize film thicknesses. Parameters, such as wrapping angle, slot gap and height, can be varied offline to achieve minimization. It is to be noted that larger wrapping angles are indirectly proportional to wet film thicknesses. 
     
       
         
           
             
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             This correlation was first applied to experimental data for Die A, and the numerical constants obtained by least-square fitting were found to be:
           Φ=0.982   b=0.50   c=0.36   d=1.38.   
         
           
         
       
    
       FIG. 21  is a schematic view of the in-line metrology and DMD (digital micromirror device) based thermal actuation to control the resist thickness profile before entering the NIL module in accordance with an embodiment of the present invention. The DMD device is useful for spatial control of the resist thickness profile to allow imprinting of patterns with varying densities or to compensate for systematic defects in the process. 
     Referring to  FIG. 21 , IR heater  2103  is used to remove the solvent in the wet film  2102  deposited on substrate  2101  via IR radiation. The imprint resist film thickness can be controlled to mitigate non-uniformities created by the slot-die coating and evaporation process. An ellipsometer/reflectometer  2105  is used to measure thickness at a location. This measurement is used as a reference to calibrate charge-coupled device (CCD) camera  2104 . CCD camera  2104  then provides large area film thicknesses based on thin film interference of broadband light (above yellow). The non-uniformity data collected can be used to actuate a DMD array and provide IR flux to compensate. 
     Feedforward models can also be built by first collecting data across several experiments and then running offline optimization routines to determine the best process conditions. Alternatively, process control can also be conducted through “machine-in-the-loop” sensing and optimization using techniques, such as neural nets, genetic algorithms, etc. After establishment of feedforward models, the use of intelligent sampling and virtual metrology techniques can be used to enable real-time automatic process control. 
     Spectral imaging and scatterometry are used to characterize and quantify defects after the NIL process and can be used for feedback and optimization. 
     Flow of a fluid in domains that have much smaller thickness than lateral length scales are adequately described by the lubrication approximation. For Marangoni, i.e., surface tension gradient, driven flows in the presence of evaporation, the lubrication approximation leads to the following equation: 
     
       
         
           
             
               
                 
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                         [ 
                         
                           
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             = 
             
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     where h=film thickness, t=time, x=spatial co-ordinate, μ=viscosity, γ=surface tension, J=mass flux across interface, ρ 1 =liquid density, and ρ v =vapor density. In this equation, temperature controls the viscosity, surface tension, densities as well as the mass flux across the interface. 
     Preliminary understanding of thin film flows in the presence of evaporation and surface tension gradients can be understood with the help of a linear stability analysis. Work done in the literature suggests that, for diffusion-limited flows, i.e., flows in which the local ambient is saturated with the vapor near the interface and evaporation is limited by diffusion of the vapor, any local film thickness perturbations are damped. This implies that non-uniform films will tend to become uniform in the absence of local substrate topography. On the other hand, for transfer-limited flows, i.e., flows in which there is advection at the interface that prevents the vapor from being saturated at the interface, the flow is unstable. This implies that troughs and valleys get amplified, which renders the film increasingly non-uniform 
     This model has been used to study and predict instabilities in the imprint resist film. In one embodiment, the thin film lubrication theory, with a surface tension boundary condition at the air-resist interface, is used. In one embodiment, the one dimensional PDE is solved using a 4 th  order Range-Kutta method. Based on appropriate heat input, instabilities can be created or mitigated in a uniform/non-uniform film. 
       FIG. 22  illustrates an in-line overlay sensing subsystem  2200  in accordance with an embodiment of the present invention. Referring to  FIG. 22 , subsystem  2200  includes a CCD camera  2201 , the edge of patterned area  2202 , stainless steel substrate  2203 , a microscope  2204 , a light source  2205 , a glass template  2206  and fixtures for microscopes  2207  (can be attached to an XY stage). 
     In one embodiment, in-line overlay sensing apparatus  2200  consists of Moiré microscopes aimed at the Moiré marks on the edges of the patterned area on the template and the edges of the imprinting area of the substrate. In one embodiment, the number of Moiré microscopes is between 6-24. The Moiré microscopes are appended with a light source  2205  and CCD camera  2201 . 
       FIG. 23  is a schematic view of the Moiré alignment marks  2301  on the template and the Moiré alignment marks  2302  on the substrate in accordance with an embodiment of the present invention. 
       FIG. 24  is a schematic view denoting a Moiré microscope apparatus suitable for embodiments with precise web handling in accordance with an embodiment of the present invention. 
     Referring to  FIG. 24 , in one embodiment, the Moiré marks are brought within the field of view  2401  of the microscopes  2402  through the web handling system. Once Moiré fringes are captured, the template housing is aligned using in-plane motion (XYθ) to achieve desired overlay. For example, given a web handling accuracy of ±10 micrometers, a 60 nm sensing resolution can be obtained using a microscope  2402  of field of view of 2 mm and P 1 , P 2  and P H  set as 40, 45 and 1 μm, respectively. If necessary, microscopes  2402  are placed on automated XY stages to ensure Moiré marks are in the field of view  2401  of microscopes  2402 .  FIG. 24  further illustrates the capture range  2405 . The capture range is intended to mean the range of misalignments from the aligned position over which alignment can be achieved. 
     In another embodiment, large bars (equal in size to Moiré fringes) are patterned on template  2403  and substrate  2404  alongside the Moiré marks. These bars are directly viewed from microscope  2402 . Moiré marks can be brought into the field of the microscopes  2402  by traversing template  2403  and substrate  2404  by observing the coarse alignment bars through microscope  2402 . 
       FIG. 25  is a schematic view denoting Moiré alignment marks with coarse alignment bars for embodiments without stringent web handling requirements in accordance with an embodiment of the present invention. 
       FIGS. 26A-26B  illustrate at-line overlay metrology apparatus  2600  in accordance with an embodiment of the present invention. 
     Referring to  FIGS. 26A-26B , apparatus  2600  includes an at-line overlay system  2601 , an imprint module  2602 , an accumulation of resist  2603  as well as an XY stage  2604  with CCD camera  2605 , a light source  2606  and microscope  2607 . 
     An at-line overlay metrology system  2601  is used to calculate the distortion of the patterned grid with respect to an ideal grid. In one embodiment, it is set up downstream of nanoimprinting module  2602 . In on embodiment, the patterning cycle is temporarily deactivated for at-line overlay measurements. A large travel stage may be used to ensure the positioning of microscope  2607  on the Moiré marks across the width of the web. In one embodiment, a small travel axis is to compensate for errors due to web distortion, stage alignment inaccuracy, etc. 
       FIG. 27  illustrates an automated mechanism for orientating idler rollers for the template web in accordance with an embodiment of the present invention. 
     Referring to  FIG. 27 , template and substrate rollers  2701  are aligned such that their axes are planar and parallel to avoid web distortion errors due to non-uniform tension along the web. In one embodiment of the setup used to align rollers  2701  to each other, each end of rollers  2701  is attached to a passive joint  2702  compliant in the planar directions (XY). For high modulus web materials, such as stainless steel and glass, uniform tension is applied along the width of the web which minimizes strain in the system and self-aligns rollers  2701 . In another embodiment, each end of roller  2701  is connected to a picomotor driven XY stage which is actively controlled to minimize misalignment. Laser tracking sensors can be used to measure misalignment between any 2 rollers in the system. 
     Referring to  FIG. 28 ,  FIG. 28  is a schematic view of vertical motion roll substrate stages for overlay correction due to rigid body motion errors in accordance with an embodiment of the present invention. 
     In one embodiment of the system, the substrate rollers mounted on a rigid frame are actuated by four voice coil actuators  2801  to achieve XYθ motion.  FIG. 28  further illustrates the stage  2802  for in-plane motion of XYθ for overlay. Linear actuators  2801  are connected to the substrate housing via a revolute flexure joint. In one embodiment, a prismatic flexure joint is used to constrain the direction of voice coil actuation. Based on feedback from the Moiré microscopes, the actuators are controlled to achieve desired overlay by producing rigid body planar motion of template  2803  with the substrate web fixed in place. The entire frame is connected to a larger frame for vertical motion actuation. 
     Furthermore,  FIG. 28  illustrates four linear actuators  2804  to achieve Z motion as well as stage  2805  for motion along z for imprint and delamination. 
       FIG. 29  illustrates a zoomed-in view of the 6 degrees of freedom flexure stage for the roll substrate describing the compliant mechanisms deployed for overlay correction in accordance with an embodiment of the present invention. 
     In another embodiment of the system, each end of the substrate is controlled via voice coil actuators to achieve controlled substrate deformation along with rigid body motion. This embodiment provides shape control and magnification control of the substrate which improves overlay. The Z-head for vertical motion is the same as in the previous embodiment discussed above. 
       FIG. 30  is a schematic of a substrate web accumulator  3001  necessary for embodiments involving overlay correction utilizing an idler roller  3002  in accordance with an embodiment of the present invention. 
     Because the disclosed process and system consists of several sub-modules, each with their own tension control requirements, in one embodiment, an accumulator  3001  is used to separate the coating and drying areas with the nanoimprint area. The nanoimprint area may undergo additional nanoprecise motion, especially for initiating contact and maintaining alignment and overlay, thus requiring the decoupling of tension in that step. For this purpose, in one embodiment, two accumulator rollers, akin to traction rollers, are proposed to compensate for processing speed differences and tension control between imprinting and coating. In one embodiment, the web hangs between the first and second accumulator rollers. 
     Substrates or film stacks, such as polycarbonate, polyethylene terephthalate (PET), etc. are nonconductive materials. These substrates or film stacks may not need precise residual layer control due to the fact that they cannot be subjected to a lot of heat during post-processing steps, such as etching and deposition, without causing undesirable distortions in the substrate. The heating of the substrates is also important to remove solvents after coating the resist film, and because of the inability of the substrates to conduct this heat, this may be transferred to the resist material setting up undesirable flow patterns and causing a loss in uniformity control. Moreover, it becomes important to heat the substrate uniformly, so that temperature gradients and consequent thermal stresses are minimized. 
     Substrates, such as Si, amorphous Si, stainless steel, etc. are conductive material. For such substrates, sub 1000-nm overlay is achievable with shape control through thermal actuators (e.g., a Peltier heater array). These substrates can conduct heat, and hence are more suited for post-processing steps, such as etching, thereby making residual layer control more feasible. Moreover, they can also lead to better heat conduction in the solvent evaporation step allowing the resist film to have a constant temperature substrate, thereby suppressing any undesirable temperature-induced flows. 
     The imprint material formulation consists of imprint resist comprising of considerable amount of components having similar volatility, dissolved in a solvent that is considerably more volatile than the rest of the components. The solvent role is to dilute the required quantity of imprint resist to higher volume thus allowing for a better way of spreading small amounts of imprint resist over the substrate and managing the final dry film thickness starting from a thicker initial wet film. Once the imprint resist solution is deposited on the substrate, the solvent evaporates first while the rest of the components evaporate at a much lower rate due to their lower volatility. This results in a mixture containing higher concentration of the other components and residual or negligible amounts of solvent. Appropriately formulated systems may perform satisfactorily under a range of compositions. Formulation design may take into account the expected amount of material that needs to be evaporated, such that the optimum range of component ratios is not disrupted. Further, certain components, such as the photoinitiator or crosslinkers, will almost always be less volatile, as seen in the table below (Table 1). 
     Besides solvents, an imprint resist formulation may contain a mixture of some, or all the following components: an initiator; polymerizable monomers with one active group; polymerizable monomers with more than one active group referred to in the art as crosslinkers; and surfactants. This list is not exhaustive as other components may be present according to desired performance and applications. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Boiling Point 
               
               
                 Role 
                 Material 
                 [° C. at 1 atm] 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 Monomers 
                 2-Ethylhexyl Methacrylate 
                 218 
               
               
                   
                 Cyclohexyl Methacrylate 
                 210 
               
               
                   
                 Isobornyl Methacrylate 
                 258 
               
               
                   
                 Tetrahydrofurfuryl Methacrylate 
                 222 
               
               
                   
                 Benzyl Methacrylate 
                 243 
               
               
                 Crosslinker 
                 Ethylene glycol Dimethacrylate 
                 240 
               
               
                 Surfactant 
                 1H,1H,2H,2H- 
                 209 
               
               
                   
                 Perfluorodecyltriethoxysilane 
               
               
                 Photoinitiators 
                 Irgacure 184 
                 &gt;300 
               
               
                   
                 Irgacure 819 
                 &gt;300 
               
               
                   
                 Irgacure 2959 
                 &gt;300 
               
               
                 Solvent 
                 MIBK 
                 117 
               
               
                   
                 Ethyl acetate 
                 77 
               
               
                   
               
            
           
         
       
     
     Downstream process considerations may preclude the use of UV-crosslinkable polymers. For example, most methacrylate polymers have a glass-transition temperature (Tg) of ˜150° C. Any downstream thermal processing beyond 150° C. may damage the material. There are other thermoset polymers, such as polyimide, that have a much higher Tg of ˜350° C. Hence, using this polymer can alleviate concerns with thermal processing. But these materials are also highly viscous, which makes them difficult to coat with substantially lower volumes. To achieve this, the polyimide material can be diluted in a solvent, which can reduce their viscosity and make the material amenable to coating. The solvent will need to be completely evaporated to minimize condensation on the substrate. This can be done by using a solvent with substantially higher volatility (e.g., methyl isobutyl ketone (MIBK), ethyl acetate) and using a heated substrate chuck or IR lamps to completely and rapidly evaporate the solvent. 
     The prevention of contamination is an important aspect of this tool, given that the nanoimprint lithography process is sensitive to particle contamination and is the last unit step in the proposed architecture. Typically, particle contamination can be minimized by maintaining a positive pressure inside the tool along with constant re-circulation. However, for this tool configuration, there will be areas of negative pressure (exhaust), especially where there is active evaporation of solvents and/or resist materials. For this purpose, the air handling inside the tool can be based on cross-flow, so that venting of air to the user is minimized while maintaining a positive pressure inside the tool. 
     A digital twin of a manufacturing tool is a model-based representation of the tool which is used to monitor and predict the performance and yield of the tool. The digital twin is often used in advanced manufacturing environments (e.g., semiconductor manufacturing) where there is availability of a substantial amount of data from the sensors in the tool. The data from the sensors is then analyzed with respect to the output of the tool (in terms of yield, performance, etc.) with the help of data analytics techniques, such that a model of the tool is constructed. This model can be completely data-based or also have a physics-based underpinning. In one embodiment, a digital twin is created for the R2P and R2R tools. 
     Furthermore, the principles of the present invention include novel techniques for fabricating large-area templates for display applications using J-FIL. 
     Display applications generally require patterning of areas significantly larger than most semiconductor applications, but allow relaxed resolution because of larger feature sizes. This permits large-area low-resolution mask-writing techniques, such as laser scribing, to be used for display photomask fabrication. Upcoming display technologies, however, pose significant challenges for the display patterning infrastructure. Developments, such as Organic Light Emitting Diodes (OLEDs), are already driving down feature resolution to sub-micrometer levels. Future developments, such as metamaterial optical elements, would most likely drive feature sizes down into the sub-50 nm regime. At this point, optical methods, such as laser scribing, would be infeasible for pattern generation. Currently, the semiconductor industry uses Electron Beam Lithography (EBL) for sub-50 nm pattern generation. However, EBL has extremely low throughput, and would be quite infeasible for making display scale masks. Additionally, large-area mask-to-substrate pattern transfer would no longer be feasible using photolithography since advanced photolithography techniques can pattern sub-50 nm features only over small areas. 
     Jet-and-Flash Imprint Lithography (J-FIL) is a next generation lithography technique that uses mechanical means to transfer patterns from a template mask onto a substrate. Feature sizes in J-FIL are not limited by the wavelength of the exposure source, and features, as small as 3 nm, have been demonstrated before. J-FIL is also not limited by pattern area, since it does not require large assemblies of focusing optics for pattern transfer. In fact, whole wafer (single-imprint) patterning of sub-10 nm features has been demonstrated using J-FIL before. Additionally, J-FIL can pattern 3-D structures in a single imprint; whereas, photolithography can only pattern 3-D structures as assemblies of multiple 2-D layers. J-FIL therefore appears to be a promising candidate, both for fabricating large-area templates, and for patterning large-area display substrates (using large-area templates). The description below will explore techniques for large-area template fabrication using J-FIL. 
     It should be noted that J-FIL, like photolithography, is simply a pattern replication method. A pattern generation technique, such as EBL, is still needed to masklessly fabricate a small unit pattern. J-FIL can then be used to tessellate a large-area template using this unit pattern, either in one sitting, or recursively. 
     It is worth mentioning that the following three layers in modern displays are the ones which are moving towards sub-50 nm (even sub-100 nm) feature sizes—polarizer layers, metal mesh layers (in touch-based displays) and thin film transistor layers. 
     Wire grid polarizers with sub-100 nm pitches are increasingly being explored for polarizer elements. Metamaterial based polarizer elements, with improved transmission efficiency, are being explored in research. Such polarizer elements would necessitate an edge-stitching precision which is some fraction of the minimum feature dimension. 
     For polarizer (and metal mesh) layers, when tessellating a large-area template using J-FIL, it is only necessary to ensure nano-precise edge-stitching, since imprecisely stitched edges could lead to light leaking through those edges and creating a visually unappealing display. Methods for achieving this are discussed further below. 
     For thin film transistor layers, large-area template fabrication using J-FIL requires registration to a global grid, instead of localized edge-stitching. Methods for achieving this are described further below. 
     The degree to which display applications are sensitive to edge-stitching errors depends on the feature sizes involved, and sensitivity of human vision in detecting large-area defect patterns. Photonic waveguides used in telecommunication, and recently in heads-up-displays as well, are sensitive to sub-100 nm edge-stitching errors. However, for polarizer and metal mesh layers, the loss in light transmission and contrast due to sub-100 nm stitching errors is generally not perceivable in an isolated polarizer or metal mesh element. However, when combined with other defective display layers, and varied viewing conditions (oblique angles, low light scenes, etc.) nanoscale stitching errors can result in visually perceivable defects and an overall unsatisfying viewing experience. Such minor fabrication errors, which are hard to quantify in strict optical terms, yet result in perceivable defects, are referred to as “mura.” Of the many types of mura, the one which is relevant here is stitch mura. 
       FIG. 31  is a schematic of a template composed of a 3×3 grid of imprinted patterns, showing various kinds of edge-stitching errors in accordance with an embodiment of the present invention. 
       FIG. 31  shows a large area template  3101  with various possible stitching error modes (rigid-body errors  3102 , higher-order stitching errors  3103 , mixed stitching errors  3104 ). The extent to which such errors effect overall display performance (contrast ratio, transmission, mura) can be evaluated using human-in-the-loop experiments, and computational-electromagnetics (CEM) techniques, such as finite-difference time-domain (FDTD), Eigenmode Expansion, etc. 
     Furthermore,  FIG. 31  shows various kinds of defects, such as the edge translation defect  3105 , edge translation defect  3106 , edge rotation defect  3107  and higher-order edge defects  3108 . Edge translation defect  3105  corresponds to a defect along the stitch edge  3109  between polarizer region 1  3110  and polarizer region 2  3111 . 
       FIGS. 32 and 33  show a generic scheme for measuring and correcting stitching errors to within the bounds derived using human-in-the-loop and CEM experiments in accordance with an embodiment of the present invention. 
     In particular,  FIG. 32  is a schematic of a large-area substrate to be tessellated with a 3×3 grid of master patterns with the first field in the process of being patterned in accordance with an embodiment of the present invention.  FIG. 33  further illustrates that alignment marks are embedded in both the wafer and template and are used for nano-precise edge stitching. 
     Furthermore, in particular,  FIG. 33  is a schematic of a master template and a large-area substrate with a dense array of alignment marks in accordance with an embodiment of the present invention. 
     Referring to  FIGS. 32 and 33 , master template  3201  contains embedded alignment marks  3202 , along with the optical patterns to be imprinted. The large-area substrate  3203 , which is to be tessellated with master template imprints, contains embedded alignment marks as well. Error sensing is achieved by measuring the relative displacement between pairs of embedded alignment marks. Error correction is achieved using stage actuators for rigid-body errors, and thermal actuators for higher-order errors. 
     The following features are worth noting about this scheme. 
     Embedded alignment marks do not get printed during the tessellation process. This ensures that the optically functional area is maximized, and no area is taken up by alignment marks, which might create noticeable periodic defects. 
     Alignment marks, in both master template  3201  and large-area substrate  3203 , are patterned in groups of two or more contiguous marks  3204 . This way, during an imprint step, the template alignment marks  3205  can be aligned to substrate alignment marks on an unpatterned region of the substrate. Additionally, because of contiguous placement of alignment marks at stitch-edges, even if a prior imprint is not perfectly aligned with the alignment grid, perfect edge-stitching could still be achieved by compensating for this prior imprint&#39;s misalignment in the current imprint. 
     In one embodiment, the master template pattern layer is index-matched to the resist, ensuring that during the in-liquid align process, patterns present underneath the alignment marks do not interfere with error measurement. 
     Depending on the level of edge-stitching precision needed, the density of alignment marks can be varied as shown in  FIG. 33 , which shows a dense alignment grid. 
     For successfully measuring the amount of edge mis-stitching, a first point on an edge of an imprint needs to be metrologically linked to an adjacent second point on the adjacent edge of the adjoining imprint. Since alignment marks cannot be patterned right at the edge of the master template field, a link between embedded alignment marks and the field edge is established as shown in  FIG. 34 . 
       FIG. 34  illustrates an exemplar fabrication sequence for the master template  3401  in accordance with an embodiment of the present invention. Referring to  FIG. 34 , master template  3401  contains two layers of patterns—the first (embedded) layer contains only alignment marks  3402 , and the second layer contains the actual optical patterns  3403 . The first layer is patterned on a quartz blank  3404  (which subsequently becomes the master template  3405 ) using a direct write method, such as e-beam lithography (EBL). Each alignment mark within a contiguous group (as indicated in  FIG. 32 ) has its relative position (to other alignment marks in the group) known to within the writing grid of the direct write tool. The second layer, which consists of optical patterns and outside-edge alignment marks, is direct written on a second quartz blank  3406 . This second pre-master template  3407  can subsequently be imprinted on the first pre-master template, with the relative position of the two templates measured using the outside-edge alignment marks (see element  3408 ). This is followed by a pattern layer etch  3409  and an etch for field edge demaracation  3410  resulting in the master template  3411 . In this way, the distance between an embedded alignment mark on the master template and its nearest edge can be derived, accurate to within (2*Δ wg +Δ 121a ). 
     A third (or fourth) pre-master template which contains a contiguous set of two or more alignment marks is used to pattern the embedded alignment mark layer on the substrate for the large-area template as shown in  FIG. 35 .  FIG. 35  illustrates an exemplar fabrication sequence for embedding alignment marks in the large area-substrate  3501  in accordance with an embodiment of the present invention. It worth noting here that the precision with which the alignment grid approaches perfect rectilinearity is dependent on the stage (X,Y,θ) motion specifications. 
     However, a non-rectilinear grid, due to an imprecise stage, can still be aligned using the alignment correction methods described further below. A schematic for how such an alignment scheme might work is shown in  FIG. 36 .  FIG. 36  illustrates an exemplar sequence for edge-stitching in a non-rectilinear substrate (alignment) grid in accordance with an embodiment of the present invention. 
     Alignment marks are patterned on the large-area substrate in groups of two, four, or more, to ensure that adjacent marks have the same misalignment from an ideal grid, if any. This relaxes the accuracy required of the motion stage, since any misalignment measured at one alignment mark can be adjusted for in the reading of the adjacent alignment mark to ensure proper stitching. 
     For example, as shown in  FIG. 36 , the misaligned pattern  3601  is aligned using stage actuation  3602  resulting in a post stage-correction  3603 . It is noted that there is some residual error, which may be left as is without affecting the final edge-stitching performance. 
     A second imprint step may then be started (see element  3604 ), where the left edge of the second imprint can be perfectly stitched with the right edge of the first imprint (using stage and thermal actuators) based on knowledge of the relative distances between alignment marks and field edges and the alignment marks themselves. The right edge of the second imprint, however, can be severely misaligned with respect to the underlying grid (see element  3605 ). The distortion of the second field during imprint (using thermal actuators) is used to align the right edge to the alignment grid (see element  3606 ). 
     However, beyond a certain limiting stage inaccuracy, the alignment method of  FIG. 40  can fail, such as shown in  FIG. 37 .  FIG. 37  illustrates exemplar scenarios where edge-stitching could fail in accordance with an embodiment of the present invention. For instance, if deviations from rectilinearity are too high, the right edge of a second imprint can simply not be within the capture range of the alignment marks (see element  3701 ). Additionally, thermal actuation might not be able to fully correct for large deviations of the master template alignment marks from the substrate marks, leading to residual errors which might accumulate over multiple imprints and eventually lead to a capture range based stitching failure (see element  3702 ). Achieving greater stage accuracy over large-areas requires not only tighter stage fabrication specifications, but also better calibration of the motion stage. 
     Any alignment mark capable of online alignment measurement with nanoscale precision could be used for edge mis-stitching detection. One possible choice could be the Moiré-based alignment marks, which have been previously used for sub-5 nm overlay in J-FIL. 
     In one embodiment, coarse stitching-error corrections can be implemented using the X, Y, θ stages. 
     Referring to  FIG. 38 ,  FIG. 38  illustrates the motion configuration with the large-area X, Y stage on the substrate side and the theta (θ) stage on the template side in accordance with an embodiment of the present invention. 
     In one embodiment, X, Y stage  3801  could be an air bearing/roller bearing/magnetic levitation stage with large-area substrate  3802  and the substrate chuck directly mounted on this stage. Theta stage  3803  for this configuration would be attached to z-head assembly  3804 . Granite base  3805 , in this embodiment, would be approximately twice the length and width of the large-area substrate. Furthermore, in one embodiment, a granite bridge  3806  is attached to granite base  3805 . In one embodiment, UV exposure would need to happen from the template side, since UV exposure from the substrate side would necessitate an open-frame X, Y stage which would lead to large bowing of the substrate chuck and substrate. 
       FIG. 39  illustrates an alternative embodiment for motion configuration with a gantry type X, Y stage on the template stage in accordance with an embodiment of the present invention. 
     Referring to  FIG. 39 , substrate  3901  and the substrate chuck is fixed to granite base  3902  with a multi-point mount  3903  and remains stationary during imprinting. Furthermore, in one embodiment, Z-head assembly  3904  is mounted on a gantry type Y stage  3905 , which could be an air bearing, roller bearing or magnetic levitation type stage. The long-stroke gantry-type stage  3905  could further have a shorter stroke stage on which z-head assembly  3904  is further mounted. In one embodiment, Z-head assembly  3904  contains mechanisms for z-axis motion and theta motion. This could be achieved either using voice coils for z-motion and a separate theta stage  3906 , or in a combined form using a hexapod assembly.  FIG. 39  further illustrates x stage  3907 . 
     In one embodiment, fine stitching-error correction can be implemented using thermal actuation. This has previously been described for semiconductor applications. Essentially, discrete regions of template and/or substrate are heated and/or cooled in a precise manner to produce nanoscale shape changes. 
       FIG. 40  illustrates an exemplar configuration for template and substrate-side thermal actuation in accordance with an embodiment of the present invention. 
     Referring to  FIG. 40 ,  FIG. 40  illustrates a z-head assembly  4000  that incudes alignment microscopes  4001  with an alignment beam  4002 . Furthermore, assembly  4000  includes voice coils  4003  for z motion with UV exposure  4004  from the sides of master template  4005 . Additionally, assembly  4000  includes a theta stage  4006  with apertures for metrology, thermal actuators  4007  and a transparent template chuck  4008 . 
     It would generally be more efficient from a control standpoint to have a high density of thermal actuators  4007  on the template side, and a low density of actuators  4007  on the substrate side. In one embodiment, the thermal actuator grid, as well as template chuck  4008 , have apertures to allow the passage of light beams for alignment mark metrology. 
     Additionally, in one embodiment, template chuck  4008  is made from transparent materials (such as transparent SiC, Sapphire, etc.), with a reflective coating on top to permit UV exposure  4004  from the side. 
     It should be noted that the choice of template and substrate materials is important in implementing a viable thermal actuation scheme. If the thermal conductivity of the template and/or large-area substrate is too low, the time for thermal corrections to take effect might be prohibitively high. Thermal conductivities of templates/substrates could be improved by etching pinholes and filling them with higher conductivity materials, such as silicon, sapphire, etc. as shown in  FIG. 41 . Such a pinhole etch, and material deposition can be achieved using standard semiconductor fabrication techniques. 
       FIG. 41  illustrates an exemplar configuration for a substrate-side pinhole array to improve thermal conductivity in accordance with an embodiment of the present invention. 
     As shown in  FIG. 41 , pinholes  4101  span the thickness of substrate  4102  except for the top pattern layer. Pinholes  4101  may be filled with thermally conductive material In one embodiment, the diameter of pinhole  4101  may be 10s of micrometers to 100s of micrometers. 
     Embodiments of the present invention also include recursive pattern transfer. 
     In case the master template pattern has a small extent (for instance, the tip-based masters are generally 10s of micrometers in extent), a recursive tessellation could be used to create larger and larger intermediate master templates, which could eventually be used to create patterns on meter scale substrates. 
     Furthermore, technologies for realizing optoelectronic devices, such as metal mesh transparent conducting electrodes, wire grid polarizers and light-trapping gratings, are limited to rigid substrates, lack the necessary patterning resolution, involve inefficient metal lift-off/etch process and/or a transfer printing steps. 
     The principles of the present invention provide the means for fabricating metallic structures on a variety of substrates both rigid and flexible. Precise control of material stack properties and process parameters allows for the continuous creation of arbitrary geometry lines and shapes consisting of metal over large areas with extremely high resolution. This can enable scalable fabrication of optoelectronic devices, such as metal mesh transparent conducting electrodes, wire grid polarizers and light-trapping gratings with superior optical, electrical and mechanical properties. Furthermore, various embodiments of the present invention enable fabrication of arbitrary nanopatterned metal films with a critical feature size in the nm scale by selective metallization on both rigid and compliant substrates. 
     Some embodiments of the present invention involve a novel combination of lithography, material stacks and process flows that incorporates interdisciplinary technologies in order to fabricate said optoelectronic devices at a commercial scale. 
     Transparent conducting electrodes (TCEs) are essential components in many optoelectronic and display technologies including light-emitting diodes, photovoltaics, and display touch screen panels. Transparent conducting oxides, specifically indium-doped tin oxide (ITO), are currently the industry standard TCE material due to their high electrical conductance and optical transparency. However, conventional ITO electrodes are intrinsically brittle, require high-temperature vacuum processing and suffer from fluctuating material costs making them undesirable for future generation optoelectronic and display devices and incompatible for flexible devices. As a result, many alternative TCEs have garnered significant research interest over the past few decades. Metal mesh-based electrodes have recently appeared as the most pragmatic solution to replace ITO for future flexible devices due to their highly tunable electrical and optical properties, low material cost and inherent mechanical robustness. However, metal mesh TCEs require high-resolution, ultra-large area nanoscale patterning on flexible polymer substrates which is beyond the capabilities of optical lithography. Moreover, commercial metal mesh electrodes will depend upon high throughput, scalable roll-to-roll (R2R) processing in order to meet the cost needs of the projected markets. 
     The present invention enables a R2R fabrication process for realizing metal nano-mesh TCEs on flexible substrates as discussed herein. In particular, embodiments of the present invention are directed to a R2R compatible fabrication process for realizing copper (CU) metal nano-mesh TCEs on flexible substrates. 
     Electroless Cu (ECu) deposition is a redox reaction consisting of an oxidation reaction of a reducing agent and a reduction reaction of Cu ions from the solution onto a catalytically activated surface. While ECu plating is an energetically favorable process, it requires a catalyst species deposited on a surface in order to reduce the activation energy of the reaction and initiate spontaneous decomposition of Cu. Therefore, ECu deposits nucleate at the sites of catalytic seed material, and films selectively grow on activated surfaces only where there is an exposed catalyst to the solution. 
     Based on exploratory experiments, it has been found that ECu is suitable for use in a R2R nanofabrication process for Cu metal nano-mesh TCEs. For example, it has been discovered that a less than 5 nm thick palladium (Pd) seed layer may be used for reliable ECu deposition of high-quality. It has further been discovered that the Pd seed layer and ECu films exhibit good adhesion to polycarbonate (PC) substrates. Additionally, it has been discovered that a Pd layer is continuous for thicknesses equal to and greater than 10 nm. Furthermore, it has been discovered that ECu films begin as isolated islands and coalesce to form a continuous layer in three distinct phases of growth: nucleation, granular merging and uniform film. Additionally, it has been discovered that the average grain size of ECu is less than 75 nm. It has further been discovered that the grain size is independent of plating time and seed layer thickness. Furthermore, it has been discovered that the deposition rate of ECu films is more than 20 nm/min. Additionally, it has been discovered that resistivity of electroless deposited copper is between ˜5-30 μΩ cm. 
     In one embodiment, selective ECu metallization is achieved by using a process, referred to herein as the “etch process approach,” by isolating certain areas of an activated surface from interacting with the plating solution. In the Etch process, the patterned imprint resist acts as the blocking layer material. UV irradiated polymerized imprint resist exhibits remarkable chemical resilience and is known to be insoluble in ECu plating solution. Moreover, the Etch process does not suffer from the geometric and microstructure limitations related to shadow-dependent oblique angle deposition. A description of the Etch process steps is provided below in connection with  FIGS. 42 and 43A-43G . 
       FIG. 42  is a flowchart of a method  4200  for selective ECu metallization in accordance with an embodiment of the present invention.  FIGS. 43A-43G  depict the cross-sectional views for selective ECu metallization using the steps described in  FIG. 42  in accordance with an embodiment of the present invention. 
     Referring to  FIG. 42 , in conjunction with  FIGS. 43A-43G , in step  4201 , a protection layer  4301  is deposited on a substrate  4302 , such as a rigid substrate (e.g., quartz) or a flexible substrate (e.g., polycarbonate (PC)), as shown in  FIGS. 43A-43B . In one embodiment, protection layer  4301  is deposited via Physical Vapor Deposition (PVD). In one embodiment, protection layer  4301  acts as a barrier between the substrate and a polymeric adhesion promoting material containing strong solvent later in the process scheme. In one embodiment, protection layer  4301  is a metal-oxide (e.g., Al 2 O 3 ). 
     In step  4202 , a palladium (Pd) seed layer  4303  is sputtered on protection layer  4301  as shown in  FIG. 43C . In one embodiment, Pd is used to catalytically activate the surface of protection layer  4301  for subsequent ECu plating. 
     In step  4203 , a polymeric adhesion promoting layer  4304  is then dispensed on Pd seed layer  4303  in order to successfully perform NIL on the Pd coated protection layer surface as shown in  FIG. 43D . The adhesion layer ensures UV cured imprint resist separates from the imprint template rather than the substrate surface during the last step in J-FIL. In wafer-scale experimentation, dispersion of the adhesion layer is completed by spin-coating, but slot-die coating can accomplish the same task for R2R processing. Adhesion layer coated samples are then cured in step  4204  at temperatures below the glass transition temperature (T g ) of PC to evaporate off solvents as shown between  FIGS. 43D and 43E . 
     In step  4205 , nanoimprint lithography (NIL) is used to transfer trench patterns  4305  on to the substrate surface (layer  4304 ) as shown in  FIG. 43E . In one embodiment, trenches have a height of approximately between 50 nm and 300 nm, linewidths between 100 nm and 900 nm and a pitch between 1 μm and 9 μm. 
     In step  4206 , samples undergo exposure to the linear ion source (LIS) equipped in the Emerson &amp; Renwick GENESIS series tool platform in order to etch the residual layer thickness (RLT) of the imprint resist layer as shown in  FIG. 43F . The LIS works by bombarding a mixture of Ar and O 2  ions towards the substrate to allow oxidation of organics and also physically mill away material. Therefore, the Pd and protection layers  4303 ,  4301  should function as an etch stop in the Etch process scheme. The LIS etch exposes Pd catalyst only at the bottom of trenches in imprint resist allowing for selective ECu deposition. 
     In step  4207 , samples are immersed in a plating solution to metallize trenches  4306  and form an interconnect embedded metal mesh electrode as shown in  FIG. 43G . 
       FIGS. 44A-44F  show results of the fabricated metal mesh on a quartz substrate using LIS exposure time and immersion in a ECu plating solution. 
       FIG. 44A  illustrates an image of patterned quartz (insert is of fields consisting of trench grids) in accordance of an embodiment of the present invention. 
       FIGS. 44B-44C  are SEM images of the fine grid pattern in accordance of an embodiment of the present invention. 
       FIGS. 44D-44F  are SEM images of the coarse grid pattern after 60 seconds of ECu plating in accordance of an embodiment of the present invention. 
     Slight Cu deposits are seen around the edge of the patterned quartz wafer in  FIG. 44A  since the Pd seed was sputtered over the entire face of the wafer but was mostly removed under exposure to the LIS. In both the fine and coarse grid geometries, high-quality selective ECu plating is observed and is continuous throughout the trenches. Defect density and the total number of defects are extremely low exemplifying the robustness of the Etch process approach. Furthermore, average Cu grain size is on par with other electroless plating films i.e., ˜45 nm. 
     An alternative embodiment to method  4200  includes depositing Pd via atomic layer deposition in the trenches before ECu plating. 
     The LIS etch process approach discussed above has successfully demonstrated selective electroless Cu deposition of high quality and uniformity within subwavelength trench geometries. Cu metal nano-mesh grids with remarkably low defect densities may be fabricated on stiff and flexible (quartz and PC) substrates using the Etch process. 
     Based on experimental work using the Etch process approach discussed above, the following has been learned. The Pd catalyst is not corrupted by application of adhesion promoting polymeric material and subsequent RLT etch by LIS exposure. The Etch process flow is capable of high-quality selective electroless Cu plating within trenches. Furthermore, LIS exposure mills the Pd seed layer in addition to organic resist and adhesion promoter layers. The LIS etch is anisotropic in the vertical and horizontal directions. 
     Consequently, the principles of the present invention provide an imprint, etch and electroless plating process for fabricating nanoscale metal mesh TCEs on flexible substrates suitable for R2R processing. Performance of fabricated metal mesh electrodes using the proposed nanofabrication process surpasses predictive models for transmittance and conductivity with significant opportunity for optimization. 
     The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.