Abstract:
Imprint lithography templates for patterning substrates are described. The templates include a section having a mold a first pattern of alignment forming areas and template alignment marks. The additional sections are generally devoid of a mold. One or more of the additional section may include the first pattern of a second pattern of alignment forming areas and template alignment marks. The second pattern may correspond to the first pattern.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is a continuation of U.S. patent application Ser. No. 11/695,850 filed Apr. 3, 2007, which claims priority to U.S. provisional application No. 60/788,806 filed on Apr. 3, 2006, both of which are incorporated herein by reference. 
     
    
     BACKGROUND INFORMATION 
       [0002]    Nano-fabrication involves the fabrication of very small structures, e.g., having features on the order of nanometers or smaller. One area in which nano-fabrication has had a sizeable impact is in the processing of integrated circuits. As the semiconductor processing industry continues to strive for larger production yields while increasing the circuits per unit area formed on a substrate, nano-fabrication becomes increasingly important. Nano-fabrication provides greater process control while allowing increased reduction of the minimum feature dimension of the structures formed. Other areas of development in which nano-fabrication has been employed include biotechnology, optical technology, mechanical systems and the like. 
         [0003]    An exemplary nano-fabrication technique is commonly referred to as imprint lithography. Exemplary imprint lithography processes are described in detail in numerous publications, such as U.S. patent application publication no. 2004/0065976 filed as U.S. patent application Ser. No. 10/264,960; U.S. patent application publication no. 2004/0065252 filed as U.S. patent application Ser. No. 10/264,926; and U.S. Pat. No. 6,936,194, entitled “Functional Patterning Material for Imprint Lithography Processes,” all of which are assigned to the assignee of the present invention. 
         [0004]    The imprint lithography technique disclosed in each of the aforementioned U.S. patent application publications and U.S. patent includes formation of a relief pattern in a polymerizable layer and transferring a pattern corresponding to the relief pattern into an underlying substrate. The substrate may be positioned upon a stage to obtain a desired position to facilitate patterning thereof. To that end, a mold is employed spaced-apart from the substrate with a formable liquid present between the mold and the substrate. The liquid is solidified to form a patterned layer that has a pattern recorded therein that is conforming to a shape of the surface of the mold in contact with the liquid. The mold is then separated from the patterned layer such that the mold and the substrate are spaced-apart. The substrate and the patterned layer are then subjected to processes to transfer, into the substrate, a relief image that corresponds to the pattern in the patterned layer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  is a simplified side view of a lithographic system having a template spaced-apart from a substrate; 
           [0006]      FIG. 2  is a simplified side view of the substrate shown in  FIG. 1 , having a patterned layer positioned thereon; 
           [0007]      FIG. 3  is a top down view of the template shown in  FIG. 1 ; 
           [0008]      FIG. 4  is a flow chart of a method of forming the template shown in  FIG. 1 ; 
           [0009]      FIG. 5  is a top down view of a master template formed from e-beam lithography, the master template employed to form template shown in  FIG. 1 ; 
           [0010]      FIG. 6  is a top down view of an intermediate substrate formed from the master template shown in  FIG. 1 ; the intermediate substrate having a first field formed and a plurality of substrate alignment marks; 
           [0011]      FIG. 7  is a top down view of the substrate alignment marks shown in  FIG. 6 ; 
           [0012]      FIG. 8  is a top down view of the master template, shown in  FIG. 1 , in superimposition with a portion of the intermediate substrate, shown in  FIG. 6 , with a mesa of the master template being in superimposition with a second field of the intermediate substrate; 
           [0013]      FIG. 9  is a top down view of the master template, shown in  FIG. 1 , in superimposition with a portion of the intermediate substrate, shown in  FIG. 6 , with a mesa of the master template being in superimposition with a third field of the intermediate substrate; 
           [0014]      FIG. 10  is a top down view of the master template, shown in  FIG. 1 , in superimposition with a portion of the intermediate substrate, shown in  FIG. 6 , with a mesa of the master template being in superimposition with a fourth field of the intermediate substrate; 
           [0015]      FIG. 11  is a top down view of the intermediate substrate, shown in  FIG. 6 , with a plurality of alignment marks being formed thereon prior to patterning the intermediate substrate; and 
           [0016]      FIG. 12  is a top down view of the master template, the master template having 9 fields associated therewith. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Referring to  FIG. 1 , a system  10  to form a relief pattern on a substrate  12  is shown. Substrate  12  may be coupled to a substrate chuck  14 . Substrate chuck  14  may be any chuck including, but not limited to, vacuum, pin-type, groove-type, or electromagnetic, as described in U.S. Pat. No. 6,873,087 entitled “High-Precision Orientation Alignment and Gap Control Stages for Imprint Lithography Processes,” which is incorporated herein by reference. In a further embodiment, substrate chuck  14  may be a chuck as described in U.S. Pat. No. 6,982,783 entitled “Chucking System for Modulating Shapes of Substrates” and U.S. Pat. No. 6,980,282 entitled “Method for Modulating Shapes of Substrates”, both of which are incorporated herein by reference. Substrate  12  and substrate chuck  14  may be supported upon a stage  16 . Further, stage  16 , substrate  12 , and substrate chuck  14  may be positioned on a base (not shown). Stage  16  may provide motion along the x and y axes. 
         [0018]    Spaced-apart from substrate  12  is a template  18  having a mold  20  extending therefrom towards substrate  20  with a patterning surface  22  thereon. Further, mesa  20  may be referred to as a mold  20 . Mesa  20  may also be referred to as a nanoimprint mold  20 . In a further embodiment, template  18  may be substantially absent of mold  20 . Template  18  and/or mold  20  may be formed from such materials including but not limited to, fused-silica, quartz, silicon, organic polymers, siloxane polymers, borosilicate glass, fluorocarbon polymers, metal, and hardened sapphire. As shown, patterning surface  22  comprises features defined by a plurality of spaced-apart recesses  24  and protrusions  26 . However, in a further embodiment, patterning surface  22  may be substantially smooth and/or planar. Patterning surface  20  may define an original pattern that forms the basis of a pattern to be formed on substrate  12 . 
         [0019]    Template  18  may be coupled to a template chuck  28 , template chuck  28  being any chuck including, but not limited to, vacuum, pin-type, groove-type, or electromagnetic, as described in U.S. Pat. No. 6,873,087. In a further embodiment, substrate chuck  14  may be a chuck as described in U.S. Pat. No. 6,982,783 and U.S. Pat. No. 6,980,282. Template chuck  28  may be coupled to an imprint head  30  to facilitate movement of template  18  and mold  20 . 
         [0020]    System  10  further comprises a fluid dispense system  32 . Fluid dispense system  32  may be in fluid communication with substrate  12  so as to deposit a polymeric material  34  thereon. System  10  may comprise any number of fluid dispensers and fluid dispense system  32  may comprise a plurality of dispensing units therein. Polymeric material  34  may be positioned upon substrate  12  using any known technique, e.g., drop dispense, spin-coating, dip coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), thin film deposition, thick film deposition, and the like. As shown, polymeric material  34  may be deposited upon substrate  12  as a plurality of spaced-apart droplets  36 . Typically, polymeric material  34  is disposed upon substrate  12  before the desired volume is defined between mold  20  and substrate  12 . However, polymeric material  34  may fill the volume after the desired volume has been obtained. 
         [0021]    Referring to  FIGS. 1 and 2 , system  10  further comprises a source  38  of energy  40  coupled to direct energy  40  along a path  42 . Imprint head  30  and stage  16  are configured to arrange mold  20  and substrate  12 , respectively, to be in superimposition and disposed in path  42 . Either imprint head  30 , stage  16 , or both vary a distance between mold  20  and substrate  12  to define a desired volume therebetween such that mold  20  contacts polymeric material  34  and the desired volume is filled by polymeric material  34 . More specifically, polymeric material  34  of droplets  36  may ingress and fill recesses  24  of mold  20 . After the desired volume is filled with polymeric material  34 , source  38  produces energy  40 , e.g., broadband ultraviolet radiation that causes polymeric material  34  to solidify and/or cross-link conforming to the shape of a surface  44  of substrate  12  and patterning surface  22 , defining a patterned layer  46  on substrate  12 . Patterned layer  46  may comprise a residual layer  48  and a plurality of features shown as protrusions  50  and recessions  52 . 
         [0022]    System  10  may further comprise an actuation system  58  surrounding template  18 /mold  20  to facilitate alignment and overlay registration between mold  20  and substrate  12 . Actuation system  58  facilitates alignment and overlay registration by selectively deforming template  18 /mold  20 . This facilitates correcting various parameters of the pattern shape, i.e., magnification characteristics, skew/orthogonality characteristics, and trapezoidal characteristics. An example of an actuation system  58  is described in U.S. Pat. No. 7,150,622 entitled “Systems for Magnification and Distortion Correction for Imprint Lithography Processes”; U.S. Pat. No. 7,170,589 entitled “Apparatus to Vary Dimensions of a Substrate During Nano-Scale Manufacturing”; and U.S. Pat. No. 6,916,585 entitled “Method of Varying Template Dimensions to Achieve Alignment During Imprint Lithography”; all of which are incorporated by reference herein. 
         [0023]    System  10  may be regulated by a processor  54  that is in data communication with stage  16 , imprint head  30 , fluid dispense system  32 , source  38 , and actuation system  58  operating on a computer readable program stored in memory  56 . 
         [0024]    Referring to  FIG. 3 , a top down view of template  18  is shown. More specifically, mold  20  of template  18  is shown comprising a plurality of dies  60 , shown as dies  60   a - 60   d . However, in a further embodiment, mold  20  may comprise any number of dies, i.e., 2, 4, 6, 8, or 9 dies. Furthermore, each of dies  60   a - 60   d  may have substantially the same relief structure  61  formed therein. To that end, formation of dies  60  of mold  20  may be formed employing e-beam lithography. However, employing e-beam lithography may result in, inter alia, increased formation time of template  18 , which may be undesirable. To that end, a method of minimizing formation time of dies  60  of mold  20  is described below. 
         [0025]    Referring to  FIGS. 3-5 , in a first embodiment, a method of forming dies  60  of mold  20  is shown. More specifically at step  100 , a master template  62  may be formed employing e-beam lithography. Master template  62  comprises a plurality of sections  64 , shown as sections  64   a - 64   d . However, in a further embodiment, master template  62  may comprise any number of sections  64 , i.e., 2, 4, 6, 8, or 9 sections. Each section of sections  64  may be separated from an adjacent section of sections  64  by a street  66 . Further, each of sections  64  may be separated from a perimeter  68  of master template  62  by a street  70 . 
         [0026]    A section of sections  64  may comprises a mesa  72  having a relief pattern  74  defined therein. As shown, mesa  72  may be positioned in section  64   a , however, in a further embodiment, mesa  72  may be positioned in any section of sections  64 . Mesa  72  comprises sides  76   a ,  76   b ,  76   c , and  76   d , with side  76   a  being positioned opposite to side  76   c  and side  76   b  being positioned opposite to side  76   d . In an example, master template  62  may have a thickness of equal to or greater than 4 mm. 
         [0027]    Master template  62  may further comprise a plurality of alignment forming areas  78  and template alignment marks  80 . Alignment forming areas  78  and template alignment marks  80  may be positioned within streets  66  and  70 . In a further embodiment, alignment forming areas  78  and template alignment marks  80  may be positioned on a plurality of mesas. In still a further embodiment, alignment forming areas  78  may comprise checkerboard forming alignment marks and template alignment marks  80  may comprise grating alignment marks. In still a further embodiment, template alignment marks  80  may be substantially planar. 
         [0028]    Positioned adjacent mesa  72  are a first subset of alignment forming areas  78  and template alignment marks  80  defining a first pattern  82   a . As shown, positioned proximate each of sides  76   a ,  76   b ,  76   c , and  76   d  are two alignment forming areas  78  and two template alignment marks  80 . However, in a further embodiment, any number of alignment forming areas  78  and template alignment marks  80  may be positioned proximate sides  76   a ,  76   b ,  76   c , and  76   d.    
         [0029]    Master template  62  may further comprise alignment forming areas  78  and template alignment marks  80  positioned in streets  66  and  70  proximate to the remaining sections  64  of master template  62 . More specifically, a second, third, and fourth subsets of alignment forming areas  78  and template alignment marks  80  may be positioned in streets  66  and  70  proximate to sections  64   b ,  64   c , and  64   d , respectively, defining a second pattern  82   b , a third pattern  82   c , and a fourth pattern  82   d , respectively. The first pattern  82   a  may be substantially the same as the third pattern  82   c  and the second pattern  82   b  may be substantially the same as the fourth pattern  82   d . Further, the first and third patterns  82   a  and  82   c  may be differ from the second and fourth patterns  82   b  and  82   d.    
         [0030]    Referring to  FIGS. 4-6 , at step  102 , polymeric material  34  may be positioned on a intermediate substrate  84  by drop dispense, spin-coating, dip coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), thin film deposition, thick film deposition, and the like. More specifically, intermediate substrate  84  may comprise a plurality of fields  86 , shown as fields  86   a - 86   d . However, in a further embodiment, intermediate substrate  84  may comprises any number of fields  86 , i.e. 2, 4, 6, 8, or 9 fields. In the present example, the number of fields  86  of intermediate substrate  84  may be substantially the same as the number of sections  64  of mater template  62 . To that end, polymeric material  34  may be positioned on field  586   a . Furthermore, polymeric material  34  may be positioned on a plurality of regions  88 , with regions laying  88  outside of fields  86   a - 86   d . In an example, intermediate substrate  84  may have a thickness of in a range of 0.05 mm to 3 mm. 
         [0031]    At step  104 , a desired spatial relationship may be obtained between master template  62  and intermediate substrate  84 , and more specifically, between field  86   a  and mesa  72 . Further at step  104 , polymeric material  34  of field  86   a  may fill the desired volume between field  86   a  of intermediate substrate  84  and mesa  72  of master template  62  and polymeric material  34  of regions  88  may fill the desired volume between regions  88  of substrate and alignment forming areas  78  of master template  62 . 
         [0032]    At step  106 , polymeric material  34  positioned on field  86   a  and regions  88  of intermediate substrate  84  may be solidified and/or cross-linked and mesa  72  of master template  62  may be separated from polymeric material  34  positioned on field  86   a , defining a patterned layer  90   a , and may be separated from polymeric material  34  positioned on regions  88 , defining substrate alignment marks  92 . As a result of intermediate substrate  84  having a thickness substantially less than a thickness of master template  62 , a separation force may be minimized, which may be desirable. 
         [0033]    Referring to  FIG. 7 , in a further embodiment, each of substrate alignment marks  92  may further comprise image placement metrology marks  94 . Image placement metrology marks  94  may be measured known image placement or image registration systems, e.g., LMS IPRO available from Leica Microsystems of Bannockburn, Ill. 
         [0034]    Referring to  FIGS. 4 ,  5 , and  8 , at step  108 , polymeric material  34  may be positioned on field  86   b  in any of the methods mentioned above with respect to  FIG. 6  and step  102 . 
         [0035]    At step  110 , a desired spatial relationship may be obtained between template alignment marks  80  of master template  62  and substrate alignment marks  92  of intermediate substrate  84  such that a desired spatial relationship between master template  62  and intermediate substrate  84  may be obtained, and more specifically, in the present example, between field  86   b  and mesa  72 . A desired spatial relationship between template alignment marks  80  and substrate alignment marks  92  may include template alignment marks  80  and substrate alignment marks  92  being in superimposition; however, in a further embodiment, template alignment marks  80  and substrate alignment marks  92  may be offset in the x-y plane a desired amount to compensate for variations among the first, second, third, and fourth patterns  82   a ,  82   b ,  82   c , and  82   d  of alignment forming areas  78  and template alignment marks  80 . 
         [0036]    Alignment between template alignment marks  80  and substrate alignment marks  92  may be determined employing an alignment system as described in U.S. Pat. No. 7,292,326 entitled “Interferometric Analysis for the Manufacture of Nano-Scale Devices,” which is incorporated herein by reference. Further at step  110 , polymeric material  34  of field  86   b  may fill the desired volume between field  86   b  of intermediate substrate  84  and mesa  72  of master template  62 . 
         [0037]    At step  112 , polymeric material  34  positioned on field  86   b  of intermediate substrate  84  may be solidified and/or cross-linked and mesa  72  of master template  62  may be separated from polymeric material  34  positioned on intermediate substrate  84 , defining a patterned layer  90   b  on field  86   b.    
         [0038]    Referring to  FIGS. 4 ,  5 , and  9 , at step  114 , polymeric material  34  may be positioned on field  86   c  in any of the methods mentioned above with respect to  FIG. 6  and step  102 . 
         [0039]    At step  116 , a desired spatial relationship may be obtained between template alignment marks  80  of master template  62  and substrate alignment marks  92  of intermediate substrate  84  such that a desired spatial relationship between master template  62  and intermediate substrate  84  may be obtained, and more specifically, in the present example, between field  86   c  and mesa  72 . To that end, to obtain a desired spatial relationship between template alignment marks  80  of master template  62  and substrate alignment marks  92 , master template  62  may be rotated about the z-axis, and more specifically, rotated 180° with respect to intermediate substrate  84 . As a result, a desired spatial relationship may be obtained between template alignment marks  80  and substrate alignment marks  92 . Further at step  116 , polymeric material  34  of field  86   c  may fill the desired volume between field  86   c  of intermediate substrate  84  and mesa  72  of master template  62 . In a further embodiment, master template  62  may be rotated prior to positioning polymeric material  34  on fields  86   c  of intermediate substrate  84 . 
         [0040]    At step  118 , polymeric material  34  positioned on field  86   c  of intermediate substrate  84  may be solidified and/or cross-linked and mesa  72  of master template  62  may be separated from polymeric material  34  positioned on field  86   a , defining a patterned layer  90   c.    
         [0041]    Referring to  FIGS. 4 and 5 , at step  120 , steps  108 ,  110 , and  112  may be repeated for field  86   d  of intermediate substrate  84 , defining patterned layer  90   d  on field  86   d . In a further embodiment, steps  108 ,  110 , and  112  may be repeated for any number of fields  86  of intermediate substrate  84 . 
         [0042]    Referring to  FIGS. 4 ,  5 , and  10 , after forming patterned layers  90   a ,  90   b ,  90   c , and  90   d  on fields  86   a ,  86   b ,  86   c , and  86   d , respectively, intermediate substrate  84  may be employed to form a pattern in a final substrate  96 . More specifically, at step  122 , polymeric material  34  may be positioned on final substrate  96  employing any of the methods mentioned above with respect to step  102  and  FIG. 6 . Final substrate  96  may comprise a plurality of fields  98 , shown as fields  98   a - 98   d . However, in a further embodiment, final substrate  96  may comprises any number of fields  98 , i.e. 2, 4, 6, 8, or 9 fields. In the present embodiment, the number of fields  98  of final substrate  96  may be substantially the same as the number of fields  86  of intermediate substrate  84 . To that end, polymeric material  34  may be positioned on fields  98  of final substrate  96 . In an example, final substrate  96  may have a thickness of equal to or greater than 4 mm. 
         [0043]    At step  124 , a desired spatial relationship may be obtained between intermediate substrate  84  and final substrate  96  such that polymeric material  34  on final substrate  96  may fill the desired volume between intermediate substrate  84  and final substrate  96 . 
         [0044]    At step  126 , polymeric material  34  positioned on final substrate  96  may be solidified and/or cross-linked and intermediate substrate  84  may be separated from polymeric material  34  positioned on final substrate  96 , defining a plurality of patterned layers  99  in each of fields  98 , with each of patterned layers  99  being substantially the same as dies  60  of mold  20 , and thus, final substrate  96  may be substantially the same as template  18 . 
         [0045]    Referring to  FIGS. 4-6 , in a second embodiment, it may be desired to form template  18  from master template  62  in a single patterning step. To that end, each of patterned layer  90  positioned on fields  86  of intermediate substrate  84  may be substantially the same as dies  60  of mold  20  and thus, intermediate substrate  84  may be substantially the same as template  18 . In the present example, master template  62  may have a thickness of approximately 2.29 mm and intermediate substrate  84  may have a thickness of 6.35 mm. 
         [0046]    Referring to  FIG. 11 , in still a further embodiment, substrate alignment marks  92  may be formed on intermediate substrate  84  in a separate step. More specifically, substrate alignment marks  92  may be formed on intermediate substrate  84  prior to forming patterned layer  90  on intermediate substrate  84 . To that end, substrate alignment marks  92  may be formed employing a) an optical lithography tool with accurate global inteferometry, such as a 913 nm scanner lithography tool available from ASML of the Netherlands or b) an optical lithography tool with excel interferometry, such as the Nanoruler described at http://www.sciencedaily.com/releases/2004/02/040203233840.htm, which is incorporated herein by reference. As a result, alignment between fields  86  of intermediate substrate  84  may be obtained, i.e., field to field alignment. 
         [0047]    Referring to  FIGS. 3 ,  5 , and  6 , to that end, as described above, mold  20  may have four dies associated therewith. However, as mentioned above, mold  20  may have any number of dies associated therewith, and thus, master template  62 , intermediate substrate  84 , and final substrate  96  may scale according. As shown in  FIG. 12 , master template  62  may have nine sections  64  associated therewith. To that end, each of sections  64  of master template  62  may have a pattern of alignment forming areas  78  and template alignment marks  80  proximate thereto, and more specifically, each section of sections  64  may have a pattern of alignment forming areas  78  and template alignment marks  80  differing from a pattern of alignment forming areas  78  and template alignment marks  80  of surrounding sections of sections  64 . More specifically, sections  64   a ,  64   c ,  64   e ,  64   g , and  64   i  may have a fifth pattern of alignment forming areas  78  and template alignment marks  80  proximate thereto and sections  64   b ,  64   d ,  64   f , and  64   h  may have a sixth pattern of alignment forming areas  78  and template alignment marks  80  proximate thereto, with the fifth pattern of alignment forming areas  78  and template alignment marks  80  being substantially the same as the first pattern mentioned above with respect to  FIG. 5 , and the sixth pattern of alignment forming areas  78  and template alignment marks  80  being substantially the same as the third pattern mentioned above with respect to  FIG. 5 . Further, each of sections  64   e ,  64   g , and  64   i  may be patterned in the above-mentioned method analogous to patterning of section  64   c  and each of sections  64   f  and  64   h  may be patterned in the above-mentioned method analogous to patterning of sections  64   b  and  64   d.    
         [0048]    Furthermore, it may be desired to minimize mechanical distortions present in template  18  formed in any of the methods mentioned above. To that end, master template  62 , intermediate substrate  84 , and final substrate  96  may be substantially flat. More specifically, master template  62 , intermediate substrate  84 , and final substrate  96  may have a flatness better than 100 nm, preferably better than 50 nm, preferably better than 20 nm and further preferably better than 10 nm over the patterning area. To further minimize the aforementioned mechanical distortions, inter alia, minimize image placement errors, intermediate substrate  84  may conform to master template  62 . To that end, master template  62 , intermediate substrate  84 , and final substrate  96  may be positioned upon a chuck analogous to substrate chuck  14  mentioned above with respect to  FIG. 1 . To that end, a shape of master template  62 , intermediate substrate  84 , and final substrate  96  may be determined employing an air gauge system (not shown) coupled with an XY stage (not shown); a laser distance sensor system (not shown) coupled with an XY stage (not shown); or a full field 3D profiler (not shown) as described in http://www.zygo.com/?/products/metrology.htm, which is incorporated by reference herein. Moreover, each of master template  62 , intermediate substrate  84 , and final substrate  96  may be formed from substantially the same material, with the material including but not limited to, fused-silica and ultra-low-expansion glass. Further, a difference in temperature between master template  62 , intermediate substrate  84 , and final substrate  96  may be less than 0.05° C., preferably less than 0.01° C., and further preferably less than 0.001° C. 
         [0049]    To further minimize, if not prevent, errors present formed in any of the methods mentioned above, in the first embodiment mentioned above, master template  62  may have an actuation system coupled thereto analogous to actuation system  58  mentioned above with respect to  FIG. 1 . In the second embodiment mentioned above, final substrate  96  may have an actuation system coupled thereto analogous to actuation system  58  mentioned above with respect to  FIG. 1 . 
         [0050]    The above-mentioned methods may be analogously employed in formation of photomasks for photolithography. Photomasks are typically 4× (the relief pattern of the photomask is 5 times the size of the desired features to be formed on the substrate). Advanced photomask that may be employed in photolithography with KrF (248 nm) laser and ArF (193 nm) laser may further comprise sub-resolution features that are smaller than the primary features. These sub-resolution features may be also known as optical proximity correction features or reticle enhanced features. The sub-resolution features do not print; they are designed to enhance the quality of the primary features. As mentioned above, the primary features are 4×. For example, for a feature of the size of 50 nm on the wafer, the primary photomask feature is 200 nm. The sub-resolution features may be as small as 1× or smaller or as large as approaching 4×. Typically the small sub-resolution features are about 1.5×; for 50 nm wafer features, this translates to 75 nm on the photomask. The 4× photomasks are for example are of size 100 mm by 100 mm for a 25 mm by 35 mm wafer field size; and 104 mm by 132 mm for a 26 mm by 33 mm wafer field size. These fields typically have 2, 4, 6, or more dies in them each of which have substantially the same pattern requirements. Thus, the above-mentioned method may be analogously employed in formation of photomasks for photolithography. 
         [0051]    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. Therefore, the scope of the invention should not be limited by the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.