Abstract:
The present invention is directed to a method of forming an imprinting layer on a substrate including high resolution features, and transferring the features into a solidified region of the substrate. Desired thickness of the residual layer may be minimized in addition to visco-elastic behavior of the material.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     
         
         
           
             This application is a Continuation of U.S. patent application Ser. No. 10/264,926 filed on Oct. 4, 2002 (now abandoned), which is hereby incorporated by reference. 
           
         
       
    
    
    
     BACKGROUND INFORMATION 
     The field of invention relates generally to imprint lithography. More particularly, the present invention is directed to forming layers on a substrate to facilitate fabrication of high resolution patterning features suited for use as metrology standards. 
     Metrology standards are employed in many industries to measure the operation of varying equipment and processes. For semiconductor processes, a typical metrology standard may include grating structures, L-shaped structures and other common patterning geometries found on production devices. In this manner, the metrology standards facilitate measurement of the performance of the processing equipment. 
     Conventional metrology standards are manufactured from a variety of conventional processes, such as e-beam lithography, optical lithography, and using various materials. Exemplary materials include insulative, conductive or semiconductive materials. After formation of the metrology standards using conventional processes, a post process characterization technique is employed to measure the accuracy of the metrology features. This is due, in part, to the difficulty in repeatably producing reliable accurate metrology standards. A drawback with the conventional processes for manufacturing metrology standards is that the post process characterization step is time consuming. In addition, the difficulty in repeatably producing reliable metrology standards results in a low yield rate. A processing technique that may prove beneficial in overcoming the drawbacks of the conventional processes for fabricating metrology standards is known as imprint lithography. 
     An exemplary imprint lithography process is disclosed in U.S. Pat. No. 6,334,960 to Willson et al. Willson et al. disclose a method of forming a relief image in a structure. The method includes providing a substrate having a planarization layer. The planarization layer is covered with a polymerizable fluid composition. A mold makes mechanical contact with the polymerizable fluid. The mold includes a relief structure, and the polymerizable fluid composition fills the relief structure. The polymerizable fluid composition is then subjected to conditions to solidify and polymerize the same, forming a solidified polymeric material on the planarization layer that contains a relief structure complimentary to that of the mold. The mold is then separated from the solid polymeric material such that a replica of the relief structure in the mold is formed in the solidified polymeric material. The planarization layer and the solidified polymeric material are subjected to an environment to selectively etch the planarization layer relative to the solidified polymeric material such that a relief image is formed in the planarization layer. Advantages with this imprint lithography process are that it affords fabrication of structures with minimum feature dimensions that are far smaller than is provided employing standard semiconductor process techniques. 
     It is desired, therefore, to provide a method for reliably producing precision features on a substrate for use as metrology standards. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified elevation view of a lithographic system in accordance with the present invention; 
         FIG. 2  is a simplified representation of material from which an imprinting layer, shown in  FIG. 1 , is comprised before being polymerized and cross-linked; 
         FIG. 3  is a simplified representation of cross-linked polymer material into which the material shown in  FIG. 2  is transformed after being subjected to radiation; 
         FIG. 4  is a simplified elevation view of the mold spaced-apart from the imprinting layer, shown in  FIG. 1 , after patterning of the imprinting layer; 
         FIG. 5  is a detailed view of the imprinting layer shown in  FIG. 4  demonstrating the non-planarity of substrate; 
         FIG. 6  is a detailed view of the imprinting layer shown in  FIG. 5  showing the transfer of the features in the imprinting layer into the substrate during an etching process; 
         FIG. 7  is a detailed view of the substrate shown in  FIG. 6  after completion of the etch process that transfers features of the imprinting layer into the substrate; 
         FIG. 8  is a perspective view of the substrate shown in  FIGS. 1-7 ; 
         FIG. 9  is a detailed view of a mold shown in  FIG. 1 , in accordance with one embodiment of the present invention; 
         FIG. 10  is a detailed view of the imprinting layer shown in  FIG. 4  using a planarization layer to overcome the non-planarity of the substrate, in accordance with a second embodiment of the present invention; 
         FIG. 11  is plan view of the substrate shown in  FIG. 10 , with a patterned imprinting layer being present; and 
         FIG. 12  is a plan view of the substrate shown in  FIG. 11  after etching of the pattern into planarization layer. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , a lithographic system in accordance with an embodiment of the present invention includes a substrate  10 , having a substantially planar region shown as surface  12 . Disposed opposite substrate  10  is an imprint device, such as a mold  14 , having a plurality of features thereon, forming a plurality of spaced-apart recessions  16  and protrusions  18 . In the present embodiment, recessions  16  are a plurality of grooves extending along a direction parallel to protrusions  18  that provide a cross-section of mold  14  with a shape of a battlement. However, recessions  16  may correspond to virtually any feature required to create an integrated circuit. A translation device  20  is connected between mold  14  and substrate  10  to vary a distance “d” between mold  14  and substrate  10 . A radiation source  22  is located so that mold  14  is positioned between radiation source  22  and substrate  10 . Radiation source  22  is configured to impinge radiation on substrate  10 . To realize this, mold  14  is fabricated from material that allows it to be substantially transparent to the radiation produced by radiation source  22 . 
     Referring to both  FIGS. 1 and 2 , a flowable region, such as an imprinting layer  24 , is disposed formed on surface  12 . Flowable region may be formed using any known technique such as a hot embossing process disclosed in U.S. Pat. No. 5,772,905, which is incorporated by reference in its entirety herein, or a laser assisted direct imprinting (LADI) process of the type described by Chou et al. in  Ultrafast and Direct Imprint of Nanostructures in Silicon , Nature, Col. 417, pp. 835-837, June 2002. In the present embodiment, however, flowable region is formed using imprint lithography. Specifically, flowable region consists of imprinting layer  24  deposited as a plurality of spaced-apart discrete beads  25  of material  25   a  on substrate  10 , discussed more fully below. Imprinting layer  24  is formed from a material  25   a  that may be selectively polymerized and cross-linked to record a desired pattern. Material  25   a  is shown in  FIG. 3  as being cross-linked at points  25   b , forming cross-linked polymer material  25   c.    
     Referring to  FIGS. 1 ,  2  and  4 , the pattern recorded by imprinting layer  24  is produced, in part, by mechanical contact with mold  14 . To that end, translation device  20  reduces the distance “d” to allow imprinting layer  24  to come into mechanical contact with mold  14 , spreading beads  25  so as to form imprinting layer  24  with a contiguous formation of material  25   a  over surface  12 . In one embodiment, distance “d” is reduced to allow sub-portions  24   a  of imprinting layer  24  to ingress into and fill recessions  16 . 
     To facilitate filling of recessions  16 , material  25   a  is provided with the requisite properties to completely fill recessions while covering surface  12  with a contiguous formation of material  25   a . In the present embodiment, sub-portions  24   a  of imprinting layer  24  in superimposition with protrusions  18  remain after the desired, usually minimum distance “d”, has been reached, leaving sub-portions  24   a  with a thickness t 1 , and sub-portions  24   b  with a thickness, t 2 . Thicknesses “t 1 ” and “t 2 ” may be any thickness desired, dependent upon the application. Typically, t 1  is selected so as to be no greater than twice width u of sub-portions  24   a , i.e., t 1 ≦2u. 
     Referring to  FIGS. 1 ,  2  and  3 , after a desired distance “d” has been reached, radiation source  22  produces actinic radiation that polymerizes and cross-links material  25   a , forming cross-linked polymer material  25   c . As a result, the composition of imprinting layer  24  transforms from material  25   a  to material  25   c , which is a solid. Specifically, material  25   c  is solidified to provide side  24   c  of imprinting layer  24  with a shape conforming to a shape of a surface  14   a  of mold  14 , shown more clearly in  FIG. 4 . 
     Referring to  FIGS. 1 ,  2  and  3  an exemplary radiation source  22  may produce ultraviolet radiation. Other radiation sources may be employed, such as thermal, electromagnetic and the like. The selection of radiation employed to initiate the polymerization of the material in imprinting layer  24  is known to one skilled in the art and typically depends on the specific application which is desired. After imprinting layer  24  is transformed to consist of material  25   c , translation device  20  increases the distance “d” so that mold  14  and imprinting layer  24  are spaced-apart. 
     Referring to  FIG. 4 , additional processing may be employed to complete the patterning of substrate  10 . For example, substrate  10  and imprinting layer  24  may be etched to increase the aspect ratio of recesses  30  in imprinting layer  24 . To facilitate etching, the material from which imprinting layer  24  is formed may be varied to define a relative etch rate with respect to substrate  10 , as desired. The relative etch rate of imprinting layer  24  to substrate  10  may be in a range of about 1.5:1 to about 100:1. Alternatively, or in addition to, imprinting layer  24  may be provided with an etch differential with respect to photo-resist material (not shown) selectively disposed on side  24   c . The photo-resist material (not shown) may be provided to further pattern imprinting layer  24 , using known techniques. Any etch process may be employed, dependent upon the etch rate desired and the underlying constituents that form substrate  10  and imprinting layer  24 . Exemplary etch processes may include plasma etching, reactive ion etching, chemical wet etching and the like. 
     Referring to  FIG. 5 , a problem addressed by the present invention concerns formation of features on substrates having extreme topologies when compared to the dimensions of features formed thereon. As a result, substrate  10  appears to present a non-planar surface  12 . This has been traditionally found in substrates formed from gallium arsenide (GAs) or indium phosphide (InP). However, as the feature dimensions decrease substrates that have historically been considered planar may present a non-planar surface to features formed thereon. For example, substrate  10  is shown with variations in surface height. The variation in height frustrates attempts to control the dimensions of features formed into substrate  10 , because of the resulting differences in distances between nadirs  130   a  and  160   a  from surface  12 , shown as h 1  and h 2 , respectively. The height differential, Δh, between surface nadir  130   a  and nadir  160   a  is defined as follows:
 
Δ h=|h   1   −h   2 |  (1)
 
Height differential, Δh, results in differing etch characteristics of vias formed into substrate  10 , discussed more fully below with respect to  FIGS. 6 and 7 .
 
     Referring to  FIGS. 5 ,  6  and  7 , transfer of the features, such as recesses  131 ,  141 ,  151 ,  161  and sub-portions  24   a , in imprinting layer  24  into substrate  10  occurs through etch processes. The height differential, Δh, results during formation of via  261  in substrate  10  before formation of the remaining vias, which will be formed in regions of substrate  10  in superimposition with recesses  131 ,  141  and  151 . This results from the time during which substrate  10  is etched during formation of vias. Specifically, nadir  160   a  reaches surface  12  of substrate  10  before the remaining nadirs  130   a ,  140   a  and  150   a . As a result an etch differential occurs, i.e., the etch process to which substrate  10  is exposed to form vias therein differs over substrate surface  12 . The etch differential is problematic, because it results in anisotropic etching that distorts the features transferred into substrate  10  from imprinting layer  24 . The distortion presents, inter alia, by variations in width w 3  between vias  231 ,  241 ,  251  and  261  formed into substrate  10 . 
     Ideally, the width of recesses  131 ,  141 ,  151  and  161 , w 1 , should be substantially similar to width w 3 . However the height differential, Δh, results in w 3  of vias  251  and  261  being greater than w 1 , as well as larger than w 3  of vias  231  and  241 . The difference between the widths w 3  of vias  231 ,  241 ,  251  and  261  defines a differential width Δw. The greater the height differential, Δh, the greater the differential width Δw. As a result Δw of via  231  and  261  is greater than Δw of vias  231  and  251 . 
     Referring to both  FIGS. 4 ,  6 ,  7  and  8 , to avoid these drawbacks, the present invention seeks to minimize the height differential Δh by minimizing layer thickness t 2  and selecting a region of substrate  10  upon which to locate and define area, A, so as to maximize the planarity of area A. Optimized production yield favors maximization of area A. However, it was determined that the smaller area, A, is made, the greater the planarity of substrate surface  12  in area, A. In short, minimization of area, A, maximizes the planarity of the same. Thus, attempts to obtain large production yields, appears to be in conflict with maximizing the planarity of area, A, because maximizing the area A reduces the planarity of surface  12  associated with area, A. 
     The manufacture of metrology standards, however, does not require large yields. Therefore, in the present embodiment of the invention, the location and size of area, A, is chosen to maximize the planarity of surface  12  in area, A of surface  12  over which vias  231 ,  241 ,  251  and  261  are formed. It is believed that by appropriately selecting area, A, over which vias  231 ,  241 ,  251  and  261  are formed, it will be possible to deposit an imprinting layer  24  of sufficiently small thickness t 2  while minimizing height differential Δh, if not abrogating the height differential Δh entirely. This provides greater control over the dimensions of recesses  131 ,  141 ,  151  and  161 , that may be subsequently formed into imprinting layer  24 , thereby affording the fabrication of features on the order of a few nanometers. 
     Referring to  FIGS. 1 ,  4  and  8 , to that end, the minimum layer thickness was chosen to avoid visco-elastic behavior of the liquid in beads  25 . It is believed that visco-elastic behavior makes difficult controlling the imprinting process. For example, the visco-elastic behavior defines a minimum thickness that layer  24  may reach, after which fluid properties, such as flow, cease. This may present by bulges in nadirs  130   a ,  140   a ,  150   a  and  160   a  as well as other problematic characteristics. In the present embodiment it was determined that providing imprinting layer  24  with a minimum thickness t 2  of no less than approximately 10 nanometers satisfied this criteria, i.e., it was the minimum thickness that could be achieved while preventing imprinting layer  24  from demonstrating visco-elastic behavior. Assuming a uniform thickness, t 2 , over layer  24 , e.g., sub-portions  24   a  and recesses  131 ,  141 ,  151  and  161  not being present so that side  24   c  is planar it was determined that the volume of liquid in beads  25  may define the planarity of side  24   d  that forms an interface with surface  12  and is disposed opposite to side  24   c . The volume is typically selected to maximize the planarity of side  24   d , which forms an interface with surface  12 . With a priori knowledge of the topology of surface  12 , the size and locus of area, A, may be chosen to maximize planarity over area A. Knowing A and the desired layer thickness t 2 , the volume, V, may be derived from the following relationship:
 
 V=At   2   (2)
 
     However, with the presence of features, such as sub-portions  24   a  and recesses  131 ,  141 ,  151  and  161 , results in layer  24  having a varying thickness over area, A. Thus, equation (2) is modified to take into consideration volumetric changes required due to the varying thickness of layer  24  over area, A. Specifically, the volume, V, is chosen so as to minimize thickness t 2 , while avoiding visco-elastic behavior and providing the requisite quantity of liquid to include features, such as sub-portions  24   a  of thickness t 1 , and recess  131 ,  141 ,  151  and  161  into layer  24 . As a result, in accordance with this embodiment of the invention, the volume, V, of liquid in beads  25  may be defined as follows:
 
 V=A ( t   2   +ft   1 )  (3)
 
where f is the fill factor and A, t 2  and t 2  are as defined above.
 
     Referring to  FIGS. 1 ,  4 ,  7 ,  8  and  9 , further control of the dimensions of features formed into substrate  10  may be achieved by proper placement and selection of recessions  16  and protrusions  18  over surface  14   a . Specifically, the arrangement of recessions  16  and protrusions  18  on mold  14  may be designed to define a uniform fill factor over mold surface  14   a . As a result, the size of etch areas will be substantially equal to the size of non-etch areas of substrate  10  in area A, where features on mold surface  14   a  are imprinted. This arrangement of features reduces, if not avoids, variations in imprinting layer  24  thickness by minimizing pattern density variations. By avoiding thickness variations in imprinting layer  24 , distortions caused by the transfer of features into substrate  10  during etch processes are reduced, if not avoided. Additional control can be obtained by having the recessions  16  and protrusions  18  formed to be periodic over surface  14   a  of mold  14 . As a result, the features transferred to imprinting layer  24  and subsequently etched into area A, i.e., vias  231 ,  241 ,  251  and  261 , fully populate and are periodic in area A. 
     It should be noted that mold surface  14   a  may be formed with uniform period features having common shapes, as well as having differing shapes, as shown. Further, recessions  16  and protrusions  18  may be arranged on mold  14  to form virtually any desired geometric pattern. Exemplary patterns include a series of linear grooves/projections  80 , a series of L-Shaped grooves/projections  82 , a series of intersecting grooves/projections defining a matrix  84 , and a series of arcuate grooves/projections  86 . Additionally, pillars  88  may project from mold  14  and have any cross-sectional shape desired, e.g., circular, polygonal etc. 
     Additionally, it is desired not to employ features as part of the metrology standards that are located proximate to the edge of imprinting layer  24  and, therefore, area A. These features become distorted when transferred into substrate  10  during etching. The distortion is produced by edge-effects due to micro-loading, thereby exacerbating control of the feature dimensions. 
     Referring to  FIGS. 7 and 8 , in another embodiment of the present invention, further control of formation of vias  231 ,  241 ,  251  and  261  may be achieved by orientating the lattice structure of substrate  10  to ensure that sidewalls  231   a ,  241   a ,  251   a  and  261   a  are orientated to be substantially parallel to one of the crystal planes of the material from which the substrate  10  is formed. For example, substrate  10  may be fabricated so that the sidewalls  231   a ,  241   a ,  251   a  and  261   a  extend parallel to either of the 100, 010 or the 110 planes. This facilitates more precise control of the width w 3  of vias  231 ,  241 ,  251  and  261  in furtherance of uniformity of the same among all features formed in area A, particularly when features of imprinting layer  24  are transferred into substrate  10  using wet etch chemistries. 
     Referring to  FIG. 1  in accordance with another embodiment of the present invention, to further provide greater control of the feature dimensions in imprinting layers  24 , it has been found that the force {right arrow over (F)} applied by mold  14  should be deminimis and only sufficient magnitude to facilitate contact with beads  25 . The spreading of liquid in beads  25  should be attributable primarily through capillary action with mold surface  14   a.    
     Referring to  FIGS. 1 ,  2  and  4 , the characteristics of material  25   a  are important to efficiently pattern substrate  10  in light of the unique deposition process that is in accordance with the present invention. As mentioned above, material  25   a  is deposited on substrate  10  as a plurality of discrete and spaced-apart beads  25 . The combined volume of beads  25  is such that the material  25   a  is distributed appropriately over area of surface  12  where imprinting layer  24  is to be formed. As a result, imprinting layer  24  is spread and patterned concurrently, with the pattern being subsequently set by exposure to radiation, such as ultraviolet radiation. It is desired, therefore, that material  25   a  has certain characteristics to facilitate even spreading of material  25   a  in beads  25  over surface  12  so that the all thicknesses t 1  are substantially uniform and all thickness t 2  are substantially uniform and all widths, w 1 , are substantially uniform. The desirable characteristics include having a suitable viscosity to demonstrate satisfaction with these characteristics, as well as the ability to wet surface of substrate  10  and avoid subsequent pit or hole formation after polymerization. To that end, in one example, the wettability of imprinting layer  24 , as defined by the contact angle method, should be such that the angle, Θ 1 , is defined as follows:
 
0&gt;Θ 1 &lt;75°  (4)
 
     With these two characteristics being satisfied, imprinting layer  24  may be made sufficiently thin while avoiding formation of pits or holes in the thinner regions of imprinting layer  24 . 
     Referring to  FIGS. 2 ,  3 ,  4  and  5 , another desirable characteristic that it is desired for material  25   a  to possess is thermal stability such that the variation in an angle Φ, measured between a nadir  30   a  of a recess  30  and a sidewall  30   b  thereof, does not vary more than 10% after being heated to 75° C. for thirty (30) minutes. Additionally, material  25   a  should transform to material  25   c , i.e., polymerize and cross-link, when subjected to a pulse of radiation containing less than 5 J cm −2 . In the present example, polymerization and cross-linking was determined by analyzing the infrared absorption of the “C═C” bond contained in material  25   a . Additionally, it is desired that substrate surface  12  be relatively inert toward material  25   a , such that less than 500 nm of surface  12  be dissolved as a result sixty (60) seconds of contact with material  25   a . It is further desired that the wetting of mold  14  by imprinting layer  24  be minimized, i.e., wetting angle, Θ 2 , be should be of requisite magnitude. To that end, the wetting angle, Θ 2 , should be greater than 75°. 
     The constituent components that form material  25   a  to provide the aforementioned characteristics may differ. This results from substrate  10  being formed from a number of different materials. As a result, the chemical composition of surface  12  varies dependent upon the material from which substrate  10  is formed. For example, substrate  10  may be formed from silicon, plastics, gallium arsenide, mercury telluride, and composites thereof. Additionally, substrate  10  may include one or more layers in region, e.g., dielectric layer, metal layers, semiconductor layer and the like. 
     Referring to  FIGS. 2 and 3 , in one embodiment of the present invention, the constituent components of material  25   a  consist of acrylated monomers or methacrylated monomers that are not silyated, a cross-linking agent, and an initiator. The non-silyated acryl or methacryl monomers are selected to provide material  25   a  with a minimal viscosity, e.g., viscosity approximating the viscosity of water (1-2 cps) or less. However, it has been determined that the speed of imprinting may be sacrificed in favor of higher accuracy in feature dimensions. As a result, a much higher viscosity material may be employed. As a result the range of viscosity that may be employed is from 1 to 1,000 centipoise or greater. The cross-linking agent is included to cross-link the molecules of the non-silyated monomers, providing material  25   a  with the properties to record a pattern thereon having very small feature sizes, on the order of a few nanometers and to provide the aforementioned thermal stability for further processing. To that end, the initiator is provided to produce a free radical reaction in response to radiation, causing the non-silyated monomers and the cross-linking agent to polymerize and cross-link, forming a cross-linked polymer material  25   c . In the present example, a photo-initiator responsive to ultraviolet radiation is employed. In addition, if desired, a silyated monomer may also be included in material  25   a  to control the etch rate of the resulting cross-linked polymer material  25   c , without substantially affecting the viscosity of material  25   a.    
     Examples of non-silyated monomers include, but are not limited to, butyl acrylate, methyl acrylate, methyl methacrylate, or mixtures thereof. The non-silyated monomer may make up approximately 25% to 60% by weight of material  25   a . It is believed that the monomer provides adhesion to an underlying organic transfer layer, discussed more fully below. 
     The cross-linking agent is a monomer that includes two or more polymerizable groups. In one embodiment, polyfunctional siloxane derivatives may be used as a cross-linking agent. An example of a polyfunctional siloxane derivative is 1,3-bis(3-methacryloxypropyl)-tetramethyl disiloxane. Another suitable cross-linking agent consists of ethylene diol diacrylate. The cross-linking agent may be present in material  25   a  in amounts of up to 20% by weight, but is more typically present in an amount of 5% to 15% by weight. 
     The initiator may be any component that initiates a free radical reaction in response to radiation, produced by radiation source  22 , shown in  FIG. 1 , impinging thereupon and being absorbed thereby. Suitable initiators may include, but are not limited to, photo-initiators such as 1-hydroxycyclohexyl phenyl ketone or phenylbis(2,4,6-trimethyl benzoyl)phosphine oxide. The initiator may be present in material  25   a  in amounts of up to 5% by weight, but is typically present in an amount of 1% to 4% by weight. 
     Were it desired to include silylated monomers in material  25   a , suitable silylated monomers may include, but are not limited to, silyl-acryloxy and silyl methacryloxy derivatives. Specific examples are methacryloxypropyl tris(tri-methylsiloxy)silane and (3-acryloxypropyl)tris(tri-methoxysiloxy)-silane. Silylated monomers may be present in material  25   a  in amounts from 25% to 50% by weight. The curable liquid may also include a dimethyl siloxane derivative. Examples of dimethyl siloxane derivatives include, but are not limited to, (acryloxypropyl)methylsiloxane dimethylsiloxane copolymer. 
     Referring to both  FIGS. 1 and 2 , exemplary compositions for material  25   a  are as follows: 
     Composition 1 
     
         
         n-butyl acrylate+(3-acryloxypropyltristrimethylsiloxy)silane+1,3-bis(3-methacryloxypropyl)tetramethyldisiloxane 
       
    
     Composition 2 
     
         
         t-n-butyl acrylate+(3-acryloxypropyltristrimethylsiloxy)silane+Ethylene diol diacrylate 
       
    
     Composition 3 
     
         
         t-butyl acrylate+methacryloxypropylpentamethyldisiloxane+1,3-bis(3-methacryloxypropyl)tetramethyldisiloxane 
       
    
     The above-identified compositions also include stabilizers that are well known in the chemical art to increase the operational life, as well as initiators. Further, to reduce distortions in the features of imprinting layer  24  due to shrinkage of material  25   a  during curing, e.g., exposure to actinic radiation such as ultraviolet radiation, silicon nano-balls may be added to the material  25   a  either before patterning, e.g., before application of beads  25  to surface  12 , or after application of beads  25  to surface  12 . 
     Referring to  FIGS. 1 ,  2  and  3 , additionally, to ensure that imprinting layer  24  does not adhere to mold  14 , surface  14   a  may be treated with a modifying agent. One such modifying agent is a release layer (not shown) formed from a fluorocarbon silylating agent. The release layer and other surface modifying agents, may be applied using any known process. For example, processing techniques that may include chemical vapor deposition method, physical vapor deposition, atomic layer deposition or various other techniques, brazing and the like. In this configuration, imprinting layer  24  is located between substrate  10  and release layer (not shown), during imprint lithography processes. 
     Referring to  FIGS. 4 and 10 , in some cases the non-planar topology of substrate  110  may frustrate deposition of an imprinting layer  24 . This may be overcome by the use of a planarization layer  125 . Planarization layer  125  functions to present a planar surface  125   a  to imprinting layer  124 , shown more clearly in  FIG. 11 . 
     Referring to both  FIGS. 10 and 11 , planarization layer  125  may be formed from a number of differing materials, such as, for example, thermoset polymers, thermoplastic polymers, polyepoxies, polyamides, polyurethanes, polycarbonates, polyesters, and combinations thereof. In the present example, planarization layer  125  is formed from an aromatic material so as to possess a continuous, smooth, relatively defect-free surface that may exhibit excellent adhesion to the imprinting layer  124 . Specifically, surface  125   a  presents a planar region upon which imprinting layer  124  may be disposed and recesses  331 ,  341 ,  351  and  361  are formed. 
     Planarization layer  125  may be disposed on substrate  110  using any known deposition technique. In the present example, planarization layer  125  is disposed on substrate  110  using spin-on techniques. However, it was discovered that during etching, that the difference in height between nadirs  330   a  and  360   a  from surface  112 , shown as h 3  and h 4 , respectively, results in differing etch characteristics of vias formed into substrate  110 , for the reasons discussed above. The height differential between surface nadir  330   a  and nadir  360   a  is defined as follows:
 
Δ h′=|h   3   −h   4 |  (5)
 
     Referring to both  FIGS. 11 and 12 , during the etching process, the features in imprinting layer  124 , such as sub-portions  224   a  are transferred into both planarization layer  125  and substrate  110 , forming sub-portions  225   a . Spaced apart between sub-portions  225   a  are vias  431 ,  441 ,  451  and  461 . Due to height differential Δh′ anisotropic etching occurs that distorts the features transferred into substrate  110  from imprinting layer  124 , as discussed above. To avoid the problems presented by the height differential Δh′ the solutions described above may apply with equal weight here. An additional advantage with providing planarization layer  125  is that it may be formulated to compensate for the anisotropicity of the etch that occurs due to the height differential, Δh, defined by equation 1. As a result, planarization layer may be employed to reduce, if not overcome, the deleterious effects of the height differential, Δh, defined by equation 1. 
     The embodiments of the present invention described above are exemplary. Many changes and modifications may be made to the disclosure recited above, while remaining within the scope of the invention. For example, as mentioned above, many of the embodiments discussed above may be implemented in existing imprint lithography processes that do not employ formation of an imprinting layer by deposition of beads of polymerizable material. Exemplary processes in which differing embodiments of the present invention may be employed include a hot embossing process disclosed in U.S. Pat. No. 5,772,905; which is incorporated by reference in its entirety herein. Additionally, many of the embodiments of the present invention may be employed using a laser assisted direct imprinting (LADI) process of the type described by Chou et al. in  Ultrafast and Direct Imprint of Nanostructures in Silicon , Nature, Col. 417, pp. 835-837, June 2002. Therefore, the scope of the invention should be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.