Abstract:
Methods of determining relative spatial parameters between two substrates in a process of alignment are described. Generally, multiple alignment data may be collected from phase information using a pair of alignment marks.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit under 35 U.S.C. §119(e)(1) of U.S. Provisional No. 60/992,521 and U.S. Provisional No. 60/992,548, which are hereby incorporated by reference. 
     
    
     BACKGROUND INFORMATION 
       [0002]    Nano-fabrication includes the fabrication of very small structures that have features on the order of 100 nanometers or smaller. One application in which nano-fabrication has had a sizeable impact is in the processing of integrated circuits. The semiconductor processing industry continues to strive for larger production yields while increasing the circuits per unit area formed on a substrate, therefore nano-fabrication becomes increasingly important. Nano-fabrication provides greater process control while allowing continued reduction of the minimum feature dimensions 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 in use today is commonly referred to as imprint lithography. Exemplary imprint lithography processes are described in detail in numerous publications, such as U.S. Patent Publication No. 2004/0065976, U.S. Patent Publication No. 2004/0065252, and U.S. Pat. No. 6,936,194, all of which are hereby incorporated by reference. 
         [0004]    An imprint lithography technique disclosed in each of the aforementioned U.S. patent publications and patent includes formation of a relief pattern in a formable layer (polymerizable) and transferring a pattern corresponding to the relief pattern into an underlying substrate. The substrate may be coupled to a motion stage to obtain a desired positioning to facilitate the patterning process. The patterning process uses a template spaced apart from the substrate and a formable liquid applied between the template and the substrate. The formable liquid is solidified to form a rigid layer that has a pattern conforming to a shape of the surface of the template that contacts the formable liquid. After solidification, the template is separated from the rigid layer such that the template and the substrate are spaced apart. The substrate and the solidified layer are then subjected to additional processes to transfer a relief image into the substrate that corresponds to the pattern in the solidified layer. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0005]    So that the present invention may be understood in more detail, a description of embodiments of the invention is provided with reference to the embodiments illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of the invention, and are therefore not to be considered limiting of the scope. 
           [0006]      FIG. 1  illustrates a simplified side view of a lithographic system in accordance with an embodiment of the present invention. 
           [0007]      FIG. 2  illustrates a simplified side view of the substrate shown in  FIG. 1  having a patterned layer positioned thereon. 
           [0008]      FIG. 3  illustrates a flow chart of an exemplary method for determining displacement from a set of phase measurements of a data source having at least two frequencies. 
           [0009]      FIG. 4  illustrates a graphical representation of phase angle change in relation to relative displacement. 
           [0010]      FIG. 5  illustrates a graphical representation of change in delta Δ in relation to relative displacement. 
           [0011]      FIG. 6  illustrates a graphical representation of minimization of delta Δ to provide displacement error. 
           [0012]      FIG. 7  illustrates exemplary linear gratings having periods capable of forming a moiré pattern. 
           [0013]      FIG. 8  illustrates exemplary linear gratings having incommensurate periods capable of forming a moiré pattern. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Referring to the figures, and particularly to  FIG. 1 , illustrated therein is a lithographic system  10  used to form a relief pattern on substrate  12 . Substrate  12  may be coupled to substrate chuck  14 . As illustrated, substrate chuck  14  is a vacuum chuck. Substrate chuck  14 , however, may be any chuck including, but not limited to, vacuum, pin-type, groove-type, electromagnetic, and/or the like. Exemplary chucks are described in U.S. Pat. No. 6,873,087, which is hereby incorporated by reference. 
         [0015]    Substrate  12  and substrate chuck  14  may be further supported by stage  16 . Stage  16  may provide motion along the x-, y-, and z-axes. Stage  16 , substrate  12 , and substrate chuck  14  may also be positioned on a base (not shown). 
         [0016]    Spaced-apart from substrate  12  is a template  18 . Template  18  may include a mesa  20  extending therefrom towards substrate  12 , mesa  20  having a patterning surface  22  thereon. Further, mesa  20  may be referred to as mold  20 . Alternatively, template  18  may be formed without mesa  20 . 
         [0017]    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, hardened sapphire, and/or the like. As illustrated, patterning surface  22  comprises features defined by a plurality of spaced-apart recesses  24  and/or protrusions  26 , though embodiments of the present invention are not limited to such configurations. Patterning surface  22  may define any original pattern that forms the basis of a pattern to be formed on substrate  12 . 
         [0018]    Template  18  may be coupled to chuck  28 . Chuck  28  may be configured as, but not limited to, vacuum, pin-type, groove-type, electromagnetic, and/or other similar chuck types. Exemplary chucks are further described in U.S. Pat. No. 6,873,087, which is hereby incorporated by reference. Further, chuck  28  may be coupled to imprint head  30  such that chuck  28  and/or imprint head  30  may be configured to facilitate movement of template  18 . 
         [0019]    System  10  may further comprise a fluid dispense system  32 . Fluid dispense system  32  may be used to deposit polymerizable material  34  on substrate  12 . Polymerizable material  34  may be positioned upon substrate  12  using techniques such as drop dispense, spin-coating, dip coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), thin film deposition, thick film deposition, and/or the like. Polymerizable material  34  may be disposed upon substrate  12  before and/or after a desired volume is defined between mold  20  and substrate  12  depending on design considerations. Polymerizable material  34  may comprise a monomer mixture as described in U.S. Pat. No. 7,157,036 and U.S. Patent Publication No. 2005/0187339, all of which are hereby incorporated by reference. 
         [0020]    Referring to  FIGS. 1 and 2 , system  10  may further comprise an energy source  38  coupled to direct energy  40  along path  42 . Imprint head  30  and stage  16  may be configured to position template  18  and substrate  12  in superimposition with path  42 . System  10  may be regulated by a processor  54  in communication with stage  16 , imprint head  30 , fluid dispense system  32 , and/or source  38 , and may operate on a computer readable program stored in memory  56 . 
         [0021]    Either imprint head  30 , stage  16 , or both vary a distance between mold  20  and substrate  12  to define a desired volume therebetween that is filled by polymerizable material  34 . For example, imprint head  30  may apply a force to template  18  such that mold  20  contacts polymerizable material  34 . After the desired volume is filled with polymerizable material  34 , source  38  produces energy  40 , e.g., broadband ultraviolet radiation, causing polymerizable material  34  to solidify and/or cross-link conforming to 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 , with protrusions  50  having thickness t 1  and residual layer having a thickness t 2 . 
         [0022]    The above-mentioned system and process may be further employed in imprint lithography processes and systems referred to in U.S. Pat. No. 6,932,934, U.S. Patent Publication No. 2004/0124566, U.S. Patent Publication No. 2004/0188381, and U.S. Patent Publication No. 2004/0211754, all of which are hereby incorporated by reference. 
       Dual Pitch Moire Phase Unwrapping 
       [0023]    Alignment between template  18  and substrate  12  may be facilitated by evaluation of moiré patterns provided by alignment marks as described in U.S. Publication No. 2004/0189996, which is hereby incorporated by reference. The presence of phase noise, camera theta, and ambiguous regions may complicate recovering absolute phase errors. There are numerous methods to unwrap, reconstruct, and/or recover phase errors within the field of interferometry and Fourier domain analysis. Algorithms, however, tend to be domain specific and generally none are applicable to alignment between templates  18  and substrates  12 . 
         [0024]      FIG. 3  illustrates a method  100  for recovering displacement from a set of phase measurements of a data source having two frequencies. In a step  102 , phase estimates Ph 1  and Ph 2  may be determined by: 
         [0000]        Ph   1   =A   1   +B   1   (EQ. 1) 
         [0000]        Ph   2   =−A   2   +B   2   (EQ. 2) 
         [0025]    As illustrated in  FIG. 4 , phase angles may change with relative displacement. In a step  104 , displacement error may be estimated by: 
         [0000]    
       
         
           
             
               
                 
                   E 
                   = 
                   
                     
                       1 
                       2 
                     
                      
                     
                       ( 
                       
                         
                           ( 
                           
                             
                               Ph 
                               1 
                             
                             × 
                             
                               
                                 P 
                                 1 
                               
                               
                                 2 
                                  
                                 Π 
                               
                             
                           
                           ) 
                         
                         - 
                         
                           ( 
                           
                             
                               Ph 
                               2 
                             
                             × 
                             
                               
                                 P 
                                 2 
                               
                               
                                 2 
                                  
                                 Π 
                               
                             
                           
                           ) 
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   
                     EQ 
                     . 
                     
                         
                     
                      
                     3 
                   
                   ) 
                 
               
             
           
         
       
     
         [0000]    If the relative shift between Ph 1  and Ph 2  is at a minimum, then B 1  and B 2  may both be equal to zero and the displacement may be calculated. If the relative shift between Ph 1  and Ph 2  is greater than the period of one or both of the frequencies, then one or both of B 1  and B 2  may be non-zero. To cancel A 1  and A 2  terms, delta Δ may be determined. In a step  106 , delta Δ may be determined by: 
         [0000]    
       
         
           
             
               
                 
                   Δ 
                   == 
                   
                     
                       1 
                       2 
                     
                      
                     
                       ( 
                       
                         
                           ( 
                           
                             
                               Ph 
                               1 
                             
                             × 
                             
                               
                                 P 
                                 1 
                               
                               
                                 2 
                                  
                                 Π 
                               
                             
                           
                           ) 
                         
                         + 
                         
                           ( 
                           
                             
                               Ph 
                               2 
                             
                             × 
                             
                               
                                 P 
                                 2 
                               
                               
                                 2 
                                  
                                 Π 
                               
                             
                           
                           ) 
                         
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   
                     EQ 
                     . 
                     
                         
                     
                      
                     4 
                   
                   ) 
                 
               
             
           
         
       
     
         [0000]    As illustrated in  FIG. 5 , delta Δ may change with relative displacement. In a step  108 , delta Δ may be minimized. For example, delta Δ may be minimized by iteratively searching the phase wrap space to find value of n 1  and n 2  wherein: 
         [0000]    
       
         
           
             
               
                 
                   
                     B 
                     1 
                   
                   = 
                   
                     ( 
                     
                       
                         2 
                          
                         Π 
                          
                         
                             
                         
                          
                         
                           n 
                           1 
                         
                       
                       
                         P 
                         1 
                       
                     
                     ) 
                   
                 
               
               
                 
                   ( 
                   
                     EQ 
                     . 
                     
                         
                     
                      
                     5 
                   
                   ) 
                 
               
             
             
               
                 
                   
                     B 
                     2 
                   
                   = 
                   
                     ( 
                     
                       
                         2 
                          
                         Π 
                          
                         
                             
                         
                          
                         
                           n 
                           2 
                         
                       
                       
                         P 
                         2 
                       
                     
                     ) 
                   
                 
               
               
                 
                   ( 
                   
                     EQ 
                     . 
                     
                         
                     
                      
                     6 
                   
                   ) 
                 
               
             
           
         
       
     
         [0026]    Ideally, delta Δ may be equal to zero. When real data is present, delta Δ may be less than a threshold value T, wherein the threshold value T is generally less than the step in delta Δ that results from a phase wrap. The dataset of  FIG. 5  illustrates how the value of delta Δ may be minimized. The result of minimizing delta Δ is the value of displacement error E (shown in  FIG. 6 ) and indicates the true difference is recovered. 
         [0027]    The procedure minimizing delta Δ may be iterative wherein an initial direction may be selected and then Ph 1  may be unwrapped with delta Δ redetermined. Additionally, as Ph 2  is unwrapped, delta Δ may be redetermined. This procedure may continue until a maximum number of unwraps is exceeded or delta Δ is less than the threshold T. If delta Δ is greater than the threshold T, then the direction may be changed and the unwrapping steps moved in the opposite direction. 
         [0028]    It should be noted that method  100  may be generalized to configurations with three phase values wherein Ph 3  similarly tracks Ph 1 . Using this configuration, phase errors introduced by camera rotation may be canceled. Additionally, method  100  may be generalized to configurations wherein Ph 1  and Ph 2  are moving in the same direction. Using this configuration, delta Δ and displacement error E may be swapped. 
       Incommensurate Moire Patterns for Template Alignment 
       [0029]    Moiré patterns may occur through two semi-transparent gratings having different periods as discussed in further detail in U.S. Publication No. 2004/0189996, which is hereby incorporated by reference. 
         [0030]    Incommensurate periods may be used to increase the capture range of a moiré mark. For example, incommensurate period may increase the amount of displacement that may be measured. 
         [0031]    Within the prior art, typically two moiré patterns are used to eliminate ambiguity in selecting a unique position during alignment of template  18  with substrate  12 . In order to create two moiré patterns, generally four gratings are used, some of which may have the same period and/or different period. As such, the two standard moiré pattern method generally works for a limited range of displacement only as the two moiré patterns may achieve minima at the same moment multiple times if displacement continues. If the periods of moiré patterns are incommensurate, however, a unique position may be determined during alignment of template  18  providing an increase in the capture range. Although the following description provides for two pairs of linear grating, it should be noted, that additional pairs of gratings may used to further increase the capture range. 
         [0032]      FIG. 7  illustrates two linear gratings with periods P 3  and P 4 . Periods P 3  and P 4  form a moiré pattern having period P M1 . Generally, the closer the periods P 3  and P 4 , the larger the period P M1 . Further, two additional linear gratings with period P 5  and P 6  (not shown) form moiré pattern having period P M2 . 
         [0033]      FIG. 8  illustrates moiré patterns wherein periods P m1  and P m2  are incommensurate resulting in patterns defined by: 
         [0000]        P   m2   ≠n ( P   m1 )  (EQ. 7) 
         [0000]    wherein n is an integer number. The equivalent positions may be represented by an oscillating function with the minima of two different moiré patterns being at the same location only once as the periods are incommensurate. Incommensurate periods provide a unique position of template  18  and/or substrate  12  at which both periods P m1  and P m2  may be aligned to a desired position. This may eliminate ambiguity in selecting the unique position during alignment of template  18 . Further, incommensurate periods may be used for automatic alignment of template  18 .