Abstract:
In nano-imprint lithography it is important to detect thickness non-uniformity of a residual layer formed on a substrate. Such non-uniformity is compensated such that a uniform residual layer may be formed. Compensation is performed by calculating a corrected fluid drop pattern.

Description:
[0001]    The present application is a continuation of U.S. patent application Ser. No. 11/694,017 filed Mar. 30, 2007, which claims priority to U.S. provisional patent application No. 60/788,808 filed Apr. 3, 2006; and the present application is also a continuation-in-part of U.S. patent application Ser. No. 11/143,092 filed Jun. 2, 2005, which claims priority to U.S. provisional patent application No. 60/579,878 filed Jun. 3, 2004. Each of the aforementioned U.S. patent applications is incorporated by reference herein. 
     
    
     BACKGROUND 
       [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 2004/0065976 filed as U.S. patent application Ser. No. 10/264,960, entitled, “Method and a Mold to Arrange Features on a Substrate to Replicate Features having Minimal Dimensional Variability”; U.S. patent application publication 2004/0065252 filed as U.S. patent application Ser. No. 10/264,926, entitled “Method of Forming a Layer on a Substrate to Facilitate Fabrication of Metrology Standards”; 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]    Imprint lithography 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 motion stage to obtain a desired position to facilitate patterning thereof. To that end, a template is employed spaced-apart from the substrate with a formable liquid present between the template and the substrate. The liquid is solidified to form a solidified layer that has a pattern recorded therein that is conforming to a shape of the surface of the template in contact with the liquid. The template is then separated from the solidified layer such that the template and the substrate are spaced-apart. The substrate and the solidified layer are then subjected to processes to transfer, into the substrate, a relief image that corresponds to the pattern in the solidified layer. 
         [0005]    The solidified layer may comprise a residual layer of material, i.e., a contiguous layer. Residual layer thickness (RLT) and residual layer thickness uniformity are key metrics for evaluating the quality of imprinted wafers. For many applications, a plasma etch step directly follows imprinting. Film thickness uniformity requirements for plasma etching are well known in the field. RLT uniformity determines the film thickness uniformity of imprinted samples to be etched. Presently, residual layer thickness uniformity is evaluated using the unaided eye to look at fringe patterns. To that end, there is no quantitative feedback to improve the residual layer uniformity once the liquid is positioned between the template and the substrate. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0006]      FIG. 1  is a simplified side view of a lithographic system having a template spaced-apart from a substrate; 
           [0007]      FIG. 2  illustrates a residual layer; 
           [0008]      FIG. 3  is a simplified elevation view of a film thickness measurement tool proximate the substrate, shown in  FIG. 1 ; 
           [0009]      FIG. 4  illustrates an image taken by the thickness measurement tool, shown in  FIG. 3 ; 
           [0010]      FIG. 5  is simplified three dimensional representation of the image, shown in  FIG. 4 ; 
           [0011]      FIG. 6  is a top down view of the substrate having a drop pattern positioned thereon; 
           [0012]      FIGS. 7A-7D  illustrate exemplary steps for addressing a non-uniform residual layer; and 
           [0013]      FIG. 8  illustrates a process for compensating for a non-uniform residual layer. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    Referring to  FIG. 1 , a system  8  to form a relief pattern on a substrate  12  includes a stage  10  upon which substrate  12  is supported and a template  14 , having a patterning surface  18  thereon. In a further embodiment, substrate  12  may be coupled to a substrate chuck (not shown), the substrate chuck (not shown) being any chuck including, but not limited to, vacuum and electromagnetic. 
         [0015]    Template  14  and/or mold  16  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  18  comprises features defined by a plurality of spaced-apart recesses  17  and protrusions  19 . However, in a further embodiment, patterning surface  18  may be substantially smooth and/or planar. Patterning surface  18  may define an original pattern that forms the basis of a pattern to be formed on substrate  12 . 
         [0016]    Template  14  may be coupled to an imprint head  20  to facilitate movement of template  14 , and therefore, mold  16 . In a further embodiment, template  14  may be coupled to a template chuck (not shown), the template chuck (not shown) being any chuck including, but not limited to, vacuum and electromagnetic. A fluid dispense system  22  is coupled to be selectively placed in fluid communication with substrate  12  so as to deposit polymeric material  24  thereon. It should be understood that polymeric material  24  may be deposited using any known technique, e.g., drop dispense, spin-coating, dip coating, chemical vapor deposition (CVD), physical vapor deposition (PVD), and the like. 
         [0017]    A source  26  of energy  28  is coupled to direct energy  28  along a path  30 . Imprint head  20  and stage  10  are configured to arrange mold  16  and substrate  12 , respectively, to be in superimposition and disposed in path  30 . Either imprint head  20 , stage  10 , or both vary a distance between mold  16  and substrate  12  to define a desired volume therebetween that is filled by polymeric material  24 . 
         [0018]    Referring to  FIGS. 1 and 2 , typically, polymeric material  24  is disposed upon substrate  12  before the desired volume is defined between mold  16  and substrate  12 . However, polymeric material  24  may fill the volume after the desired volume has been obtained. After the desired volume is filled with polymeric material  24 , source  26  produces energy  28 , e.g., broadband energy that causes polymeric material  24  to solidify and/or cross-link conforming to the shape of a surface  25  of substrate  12  and patterning surface  18 , defining a patterned layer  50  on substrate  12  having a contiguous formation of polymeric material  24  over surface  25 . More specifically, patterned layer  50  comprises sub-portions  34   a  and  34   b , with sub-portions  34   b  being in superimposition with protrusions  19 , with sub-portions  34   a  having a thickness t 1  and sub-portions  34   b  having a thickness t 2 , with sub-portions  34   b  commonly referred to as the residual layer. Thicknesses t 1  and t 2  may be any thickness desired, dependent upon the application. 
         [0019]    Referring to  FIGS. 1 ,  2 , and  3 , the broadband energy may comprise an actinic component including, but not limited to, ultraviolet wavelengths, thermal energy, electromagnetic energy, visible light and the like. The actinic component employed is known to one skilled in the art and typically depends on the material from which imprinting layer  12  is formed. Control of this process is regulated by a processor  32  that is in data communication with stage  10 , imprint head  20 , fluid dispense system  22 , source  26 , operating on a computer readable program stored in memory  34 . System  8  may further include a film thickness measurement tool  60  coupled with the substrate chuck (not shown), described further below. Film thickness measurement tool  60  may comprise an optical detection system, and further may be in data communication with processor  32 . Film thickness measurement tool  60  may be a stand alone tool commonly used in semiconductor fabrication. Such tools are commercially available from Metrosol, Inc., Filmetrics, Rudolph Technologies, and J.A. Woolam. 
         [0020]    Patterned layer  50  may have variations among thicknesses t 2 , which may be undesirable. More specifically, minimizing, if not preventing, variations among sub-portions  34   b , and thus, the residual layer may result in improved control of the critical dimension of pattered layer  50 , which may be desired. In an example, it may be desirable to reduce variations among sub-portions  34   b  below the approximately 30 nm level seen in typical imprints in order to minimize, if not prevent, the impact to etched feature critical dimension. 
         [0021]    To that end, variations in thicknesses t 2  of sub-portions  34   b  may be measured generating measured data, with the measured data facilitating a design in positioning of polymeric material  24  upon substrate  12 . In the present embodiment, polymeric material  24  is positioned as a plurality of droplets upon substrate  12 , and thus, the measured data facilitates a design in the drop pattern of polymeric material  24 . As a result, uniformity in thicknesses t 2  of the sub-portions  34   b  may be achieved. 
         [0022]    The variations in thicknesses t 2  of sub-portions  34   b  may be measured at a plurality of points employing film thickness measurement tool  60 , with the optical detection system digitizing imprinted fields, i.e., patterned layer  50 , and subsequently employing processor  32  operating on a computer readable program stored in memory  34  to analyze said imprinted fields to construct a map of the thickness t 2  of sub-portions  34   b  across patterned layer  50 . To that end, the drop pattern of polymeric material  24  may be varied, i.e., droplets may be added or subtracted, the drop offset may be varied, individual drop volumes of the plurality of drops, based upon the variations in thickness t 2  of sub-portions  34   b  to generate a drop pattern that may facilitate patterned layer  50  comprising sub-portions  34   b  having a desired thickness uniformity. 
         [0023]    Referring to  FIGS. 1 and 3 , to that end, film thickness measurement tool  60  may be positioned at a fixed angle and distance from substrate  12 , with the distance from the imprint field, i.e., patterned layer  50 , to film thickness measurement tool  60  being calculated. A calibration process may be required to obtain accurate dimensions of the imprint field. An alternative method for measuring the residual layer thickness measures the optical properties of the film, such as reflected intensity versus wavelength or circular versus elliptical polarization of light reflected from the field. These spectroscopic measurements are then fit to a model of the film stack to determine parameters of interest such as film thickness. Such a process can be implemented using the commercially available film thickness measurement tools noted above. 
         [0024]    Referring to  FIGS. 1 and 4 , after an image of the imprint field is taken by film thickness measurement tool  60 , processor  32  operating on a computer readable program stored in memory  34  may employ an algorithm to convert the image into a square (or, rectangle, circular, etc.) imprint area. Subsequently, processor  32  may convert differences in color and shade grades into a Z-height profile of the imprint field.  FIG. 5  shows an example of a three-dimensional representation of the field shown in  FIG. 4 . Furthermore, the computer readable program stored in memory  34  may comprise a program entitled ImageJ available from http://rsb.info.nih.gov/ij/. 
         [0025]    Further analysis of the imprinted filed is performed to map surface  25  of substrate  12  with a polynomial two-dimensional function, f(x,y). In this way, we can assign a specific thickness to each (x,y) point. Further, an average g(x,y) may be calculated, as well as deviation from this average: w(x,y)=g(x,y)−f(x,y). 
         [0026]    The slope g(x,y) will be used to calculate the offsets in X and Y directions of the drop pattern. Deviation function w(x,y) will be used to control local unit fluid volume; number of drops, position of drops and drop volume itself. 
         [0027]      FIG. 6  shows an exemplary drop pattern of polymeric material  24  used for imprinting that produced a desired thickness profile shown on  FIG. 5 . Using a multi-nozzle dispensing unit, various drop patterns can be generated on the substrate, such as a uniform grid superimposed with localized compensating drops. 
         [0028]    Furthermore, the drop pattern on  FIG. 6  corresponds to the following drop matrix, M(x,y): 
         [0029]    1: (0, 0) 3.3113E-4 uL (microliters)×29 drops
       (0,0) refers to the center of the template       
 
         [0031]    2: (−0.95, 0.95) 3.3113E-4 uL×6 
         [0032]    3: (−0.65, 0.95) 3.3113E-4 uL×15 
         [0033]    4: (−0.95, 0.65) 3.3113E-4 uL×6 
         [0034]    5: (−0.73, 0.73) 3.3113E-4 uL×15 
         [0035]    6: (−0.56, 0.56) 3.3113E-4 uL×16 
         [0036]    7: (−0.4, 0.4) 3.3113E-4 uL×13 
         [0037]    8: (−0.24, 0.26) 3.3113E-4 uL×6 
         [0038]    9: (0, 0.32) 3.3113E-4 uL×6 
         [0039]    10: (0, 0.52) 3.3113E-4 uL×13 
         [0040]    11: (−0.15, 1) 3.3113E-4 uL×7 
         [0041]    12: (0, 0.8) 3.3113E-4 uL×20 
         [0042]    13: (0.15, 1) 3.3113E-4 uL×7 
         [0043]    14: (0.65, 0.95) 3.3113E-4 uL×15 
         [0044]    15: (0.95, 0.95) 3.3113E-4 uL×6 
         [0045]    16: (0.95, 0.65) 3.3113E-4 uL×6 
         [0046]    17: (0.73, 0.73) 3.3113E-4 uL×15 
         [0047]    18: (0.56, 0.56) 3.3113E-4 uL×13 
         [0048]    19: (0.4, 0.4) 3.3113E-4 uL×13 
         [0049]    20: (0.24, 0.26) 3.3113E-4 uL×6 
         [0050]    21: (0.3, 0) 3.3113E-4 uL×6 
         [0051]    22: (0.5, 0) 3.3113E-4 uL×13 
         [0052]    23: (1, 0.15) 3.3113E-4 uL×7 
         [0053]    24: (0.8, 0) 3.3113E-4 uL×15 
         [0054]    25: (1, −0.15) 3.3113E-4 uL×7 
         [0055]    26: (0.95, −0.65) 3.3113E-4 uL×6 
         [0056]    27: (0.95, −0.95) 3.3113E-4 uL×6 
         [0057]    28: (0.65, −0.95) 3.3113E-4 uL×10 
         [0058]    29: (0.73, −0.73) 3.3113E-4 uL×15 
         [0059]    30: (0.56, −0.56) 3.3113E-4 uL×13 
         [0060]    31: (0.4, −0.4) 3.3113E-4 uL×13 
         [0061]    32: (0.24, −0.26) 3.3113E-4 uL×6 
         [0062]    33: (0, −0.32) 3.3113E-4 uL×6 
         [0063]    34: (0, −0.52) 3.3113E-4 uL×13 
         [0064]    35: (0.15, −1) 3.3113E-4 uL×7 
         [0065]    36: (0, −0.8) 3.3113E-4 uL×15 
         [0066]    37: (−0.15, −1) 3.3113E-4 uL×7 
         [0067]    38: (−0.24, −0.26) 3.3113E-4 uL×6 
         [0068]    39: (−0.4, −0.4) 3.3113E-4 uL×13 
         [0069]    40: (−0.56, −0.56) 3.3113E-4 uL×19 
         [0070]    41: (−0.73, −0.73) 3.3113E-4 uL×15 
         [0071]    42: (−0.65, −0.95) 3.3113E-4 uL×10 
         [0072]    43: (−0.95, −0.95) 3.3113E-4 uL×6 
         [0073]    44: (−0.95, −0.65) 3.3113E-4 uL×6 
         [0074]    45: (−1, −0.15) 3.3113E-4 uL×7 
         [0075]    46: (−0.8, 0) 3.3113E-4 uL×20 
         [0076]    47: (−1, 0.15) 3.3113E-4 uL×7 
         [0077]    48: (−0.5, 0) 3.3113E-4 uL×13 
         [0078]    49: (−0.3, 0) 3.3113E-4 uL×6 
         [0079]    To that end, to compensate for variations among thicknesses t 2  of sub-portions  34   b , the following may be employed: 
         [0080]    1. Use function g(x,y) to calculate drop pattern offset represented as a vector S: 
         [0000]        S=−A  grad( g ( x,y )) i−B  grad( g ( x,y )) j,    
         [0081]    where i and j are the unit vectors along X and Y axes. A, B are the proportionality coefficients that need to be determined experimentally, for instance, using a blank mesa template. Imprint new field and measure g(x,y) again. Verify that the slope in X and Y is near zero. 
         [0082]    2. After gradient of function g(x,y) is minimized, individual drop volumes are addressed. Multiply the drop pattern matrix M(x,y) by function w′(x,y), where: 
         [0000]        w ′( x,y )= w ( x,y )/(max( w ( x,y ))−min( w ( x,y ))) 
         [0083]    So new drop pattern M′(x,y) will be: 
         [0000]        M ′( x,y )= M ( x,y )* w ′( x,y ) 
         [0084]    3. Verify that the new imprint has uniform thickness by measuring the slope of g(x,y) and minimizing function w(x,y). 
         [0085]    A process for obtaining a uniform residual layer thickness (RLT) is illustrated in  FIGS. 7A-7D  and  8 . In step  801 , the imprint tool is calibrated to determine how much fluid to dispense to make an imprint with a desired thickness. In step  802 , a uniform distribution of fluid is deposited on the substrate as illustrated in  FIG. 7A . An imprint is performed. Evaporation and other non-uniformities may cause the RLT to be non-uniform. In step  803 , RLT uniformity is measured across a dense array of points in the imprinted field using the film thickness measurement tool  60 . In step  804 , if a desired uniformity is achieved, then the process may end in step  805 . If not (see  FIG. 7B ), then the process proceeds to step  806 , where one of the above algorithms is employed, such as in software running in processor  32 , to calculate a new corrected drop pattern, which will add drops, or increase drop size, to thin areas and/or remove drops, or decrease drop size, from thick areas to achieve improved RLT uniformity. The process then returns to step  802  to make a new imprint using the corrected drop pattern (see  FIG. 7C ), and steps  803  and  804  are performed again. This process may be repeated as needed until a desired uniformity RLT is achieved, as illustrated in  FIG. 7D . 
         [0086]    This above-mentioned method may be employed to obtain a desired volume of polymeric fluid  24  positioned upon substrate  12  to the volume of features (protrusions  17  and recesses  19 ) in mold  16 . In a further embodiment, the above-mentioned method may be employed to compensate for evaporation in the plurality of droplets of polymeric material  24  after positioning the same upon substrate  12  and prior to contact with mold  16 . In both cases, matching a volume of polymeric material  24  upon substrate  12  to the volume of features in mold  16  result in improved residual layer uniformity, i.e., variations among thicknesses t 2  of sub-portions  34   b . This improved residual layer uniformity enables better control of feature CDs across imprinted and etched wafers. Furthermore, the above-mentioned may also minimize, if not reduce, and impact of faceting during a breakthrough etch of the residual layer. 
         [0087]    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.