Abstract:
Methods of imprint lithography are described. Generally, the methods include imprinting, via a patterned mold, a pattern into a polymerizable fluid composition on a substrate to form a patterned imprinting layer. A conformal layer is overlayed on the patterned imprinting layer. A portion of the conformal layer is used as a hard mask for subsequent processing. The imprinted pattern may be transferred to the substrate by a plurality of etches.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
       [0001]    This application is a continuation of U.S. Ser. No. 12/689,773, filed Jan. 19, 2010, which is a continuation of U.S. Pat. No. 7,670,953, filed Aug. 24, 2007, which is a continuation of U.S. Pat. No. 7,323,417, filed Dec. 15, 2006, which is a continuation of U.S. Pat. No. 7,186,656, filed Sep. 21, 2004, which is a continuation-in-part of U.S. Ser. No. 10/850,876, filed on May 21, 2004 (abandoned). U.S. Pat. No. 7,670,953 is also a continuation of U.S. Pat. No. 7,261,831, filed Nov. 17, 2006, which is a continuation of U.S. Pat. No. 7,179,396, filed Mar. 25, 2003. All of the aforementioned applications and patents are incorporated herein by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The field of invention relates generally to micro-fabrication of structures. More particularly, the present invention is directed to patterning substrates in furtherance of the formation of structures. 
         [0003]    Micro-fabrication involves the fabrication of very small structures, e.g., having features on the order of micro-meters or smaller. One area in which micro-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, micro-fabrication becomes increasingly important. Micro-fabrication provides greater process control while allowing increased reduction of the minimum feature dimension of the structures formed. Other areas of development in which micro-fabrication has been employed include biotechnology, optical technology, mechanical systems and the like. 
         [0004]    An exemplary micro-fabrication technique is shown 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 transfer layer. The transfer layer is covered with a polymerizable fluid composition. An imprint device makes mechanical contact with the polymerizable fluid. The imprint device includes a relief structure formed from lands and grooves. The polymerizable fluid composition fills the relief structure, with the thickness of the polymerizable fluid in superimposition with the lands defining a residual thickness. The polymerizable fluid composition is then subjected to conditions to solidify and polymerize the same, forming a solidified polymeric material on the transfer layer that contains a relief structure complimentary to that of the imprint device. The imprint device is then separated from the solid polymeric material such that a replica of the relief structure in the imprint device is formed in the solidified polymeric material. The transfer layer and the solidified polymeric material are subjected to an environment to selectively etch the transfer layer relative to the solidified polymeric material such that a relief image is formed in the transfer layer. Thereafter, conventional etching processes may be employed to transfer the pattern of the relief structure into the substrate. 
         [0005]    It is desired to minimize dimensional variations between the pattern recorded in the polymeric material from the pattern transferred into the substrate, referred to as transfer distortions. To that end, many attempts have been made to advance the micro-fabrication technique of Willson et al. For example, it has been desired to minimize the residual thickness of the solidified polymeric material. The thinner the residual thickness, the greater reduction in transfer distortions. The residual thickness of the solidified polymeric material is proportional to the residual thickness of the polymerizable fluid. However, the rate at which the polymerizable fluid fills the relief structure is inversely proportional to the cube of the residual thickness of polymerizable fluid. It is manifest that minimizing the transfer distortions increases the time required to record the pattern in the substrate. Thus, a tradeoff exists between throughput and minimization of transfer distortions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a perspective view of a lithographic system in accordance with the present invention; 
           [0007]      FIG. 2  is a simplified elevation view of a lithographic system, shown in  FIG. 1 , employed to create a patterned imprinting layer in accordance with the present invention; 
           [0008]      FIG. 3  is a simplified representation of material from which a patterned imprinting layer, shown in  FIG. 2 , is comprised before being polymerized and cross-linked in accordance with the present invention; 
           [0009]      FIG. 4  is a simplified representation of cross-linked polymer material into which the material shown in  FIG. 3  is transformed after being subjected to radiation in accordance with the present invention; 
           [0010]      FIG. 5  is a simplified elevation view of an imprint device spaced-apart from the patterned imprinting layer, shown in  FIG. 1 , after patterning in accordance with the present invention; 
           [0011]      FIG. 6  is a simplified elevation view of a lithographic system, shown in  FIG. 1 , after formation of a multi-layered structure by deposition of a conformal layer, adjacent to the patterned imprinting layer, employing a mold in accordance with one embodiment of the present invention; 
           [0012]      FIG. 7  is a simplified elevation view after a blanket etch of the multi-layered structure, shown in  FIG. 6 , after formation of a crown surface in the conformal layer with portions of the patterned imprinting layer being exposed in accordance with one embodiment of the present invention; 
           [0013]      FIG. 8  is a simplified elevation view of the multi-layered structure, shown in  FIG. 7 , after subjecting the crown surface to an anisotropic etch to expose regions of a substrate in accordance with the present invention; 
           [0014]      FIG. 9  is a simplified elevation view of material in an imprint device and substrate employed with the present invention in accordance with an alternate embodiment of the present invention; 
           [0015]      FIG. 10  is a simplified elevation view of a lithographic system, shown in  FIG. 1 , after formation of a multi-layered structure by deposition of a conformal layer, adjacent to the patterned imprinting layer, employing a planarized mold in accordance with an alternate embodiment of the present invention; and 
           [0016]      FIG. 11  is a simplified elevation view of a multi-layered structure after deposition of a conformal layer in accordance with an alternate embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]      FIG. 1  depicts a lithographic system  10  in accordance with one embodiment of the present invention that includes a pair of spaced-apart bridge supports  12  having a bridge  14  and a stage support  16  extending therebetween. Bridge  14  and stage support  16  are spaced-apart. Coupled to bridge  14  is an imprint head  18 , which extends from bridge  14  toward stage support  16 . Disposed upon stage support  16  to face imprint head  18  is a motion stage  20 . Motion stage  20  is configured to move with respect to stage support  16  along X and Y axes. A radiation source  22  is coupled to system  10  to impinge actinic radiation upon motion stage  20 . As shown, radiation source  22  is coupled to bridge  14  and includes a power generator  23  connected to radiation source  22 . 
         [0018]    Referring to both  FIGS. 1 and 2 , connected to imprint head  18  is a substrate  26  having a patterned mold  28  thereon. Patterned mold  28  includes a plurality of features defined by a plurality of spaced-apart recesses  28   a  and projections  28   b.  Projections  28   b  have a width W 1 , and recesses  28   a  have a width W 2 , both of which are measured in a direction that extends transversely to Z axis. The plurality of features defines an original pattern that is to be transferred into a wafer  31  positioned on motion stage  20 . To that end, imprint head  18  is adapted to move along the Z axis and vary a distance “d” between patterned mold  28  and wafer  31 . Alternatively, or in conjunction with imprint head  18 , motion stage  20  may move substrate  26  along the Z-axis. In this manner, the features on patterned mold  28  may be imprinted into a flowable region of wafer  31 , discussed more fully below. Radiation source  22  is located so that patterned mold  28  is positioned between radiation source  22  and wafer  31 . As a result, patterned mold  28  is fabricated from material that allows it to be substantially transparent to the radiation produced by radiation source  22 . 
         [0019]    Referring to both  FIGS. 2 and 3 , a flowable region, such as a patterned imprinting layer  34 , is disposed on a portion of surface  32  that presents a substantially planar profile. 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 consists of patterned imprinting layer  34  being deposited as a plurality of spaced-apart discrete beads  36  of material  36   a  on wafer  31 , discussed more fully below. Patterned imprinting layer  34  is formed from a substantially silicon-free material  36   a  that may be selectively polymerized and cross-linked to record the original pattern therein, defining a recorded pattern. Material  36   a  is shown in  FIG. 4  as being cross-linked at points  36   b,  forming cross-linked polymer material  36   c.    
         [0020]    Referring to  FIGS. 2 ,  3  and  5 , the pattern recorded in patterned imprinting layer  34  is produced, in part, by mechanical contact with patterned mold  28 . To that end, imprint head  18  reduces the distance “d” to allow patterned imprinting layer  34  to come into mechanical contact with patterned mold  28 , spreading beads  36  so as to form patterned imprinting layer  34  with a contiguous formation of material  36   a  over surface  32 . In one embodiment, distance “d” is reduced to allow sub-portions  34   a  of patterned imprinting layer  34  to ingress into and fill recesses  28   a.    
         [0021]    To facilitate filling of recesses  28   a,  material  36   a  is provided with the requisite properties to completely fill recesses  28   a  while covering surface  32  with a contiguous formation of material  36   a.  In the present embodiment, sub-portions  34   b  of patterned imprinting layer  34  in superimposition with projections  28   b  remain after the desired, usually minimum distance “d”, has been reached, leaving sub-portions  34   a  with a thickness, t 1  and sub-portions  34   b  with a thickness, t 2 . Thickness t 2  is referred to as a residual thickness. Thicknesses “t 1 ” and “t 2 ” may be any thickness desired, dependent upon the application. 
         [0022]    Referring to  FIGS. 2 ,  3  and  4 , after a desired distance “d” has been reached, radiation source  22  produces actinic radiation that polymerizes and cross-links material  36   a,  forming cross-linked polymer material  36   c.  As a result, the composition of patterned imprinting layer  34  transforms from material  36   a  to material  36   c,  which is a solid. Specifically, material  36   c  is solidified to provide side  34   c  of patterned imprinting layer  34  with a shape conforming to a shape of a surface  28   c  of patterned mold  28 , shown more clearly in  FIG. 5 , with patterned imprinting layer  34  having recessions  30   a  and protrusions  30   b.  After patterned imprinting layer  34  is transformed to consist of material  36   c,  shown in  FIG. 4 , imprint head  18 , shown in  FIG. 2 , is moved to increase distance “d” so that patterned mold  28  and patterned imprinting layer  34  are spaced-apart. 
         [0023]    In a further embodiment, recessions  30   a  and protrusions  30   b  of imprinting layer  34  may be formed by such techniques including, but not limited to, photolithography (various wavelengths including G line, I line, 248 nm, 193 nm, 157 nm, and 13.2-13.4 nm), e-beam lithography, x-ray lithography, ion-beam lithography, and atomic beam lithography. 
         [0024]    Referring to  FIG. 6 , additional processing is employed to form a multi-layered structure  38  by forming a conformal layer  40  adjacent to patterned imprinting layer  34 . One manner in which to form conformal layer  40  is to employ imprint lithography processes, such as those discussed above with respect to depositing patterned imprinting layer  34 . To that end, conformal layer  40  may be formed from a polymerizable material similar to that described above with respect to  FIGS. 3 and 4 , excepting that the material from which conformal layer  40  is formed includes silicon, i.e., is a silicon-containing polymerizable material. Conformal layer  40  includes first and second opposed sides. First side  40   b  faces patterned imprinting layer  34  and has a profile complementary to the profile of the patterned imprinting layer  34 . The second side faces away from patterned imprinting layer  34  forming normalization surface  40   a.  Normalization surface  40   a  is provided with a substantially normalized profile, by ensuring that the distances, k 2 , k 4 , k 6 , k 8  and k 10 , between the apex  30   c,  shown in  FIG. 5 , of each of the protrusions  30   b  and normalization surface  40   a  are substantially the same and that the distance, k 1 , k 3 , k 5 , k 7 , k 9  and k 11  between a nadir surface  30   d  of each of the recessions  30   a  and normalization surface  40   a  are substantially the same. 
         [0025]    One manner in which to provide normalization surface  40   a  with a normalized profile, a planarizing mold  128  having a planar surface  128   a  is employed to come into contact with conformal layer  40 . As mentioned above, this may be accomplished by moving imprint head  18 , shown in  FIG. 2 , along the Z-axis, moving motion stage  20  along the Z-axis, or both. Thereafter, mold  128  is separated from conformal layer  40  and actinic radiation impinges upon conformal layer  40  to polymerize and, therefore, solidify the same. Alternatively, conformal layer  40  may be applied employing spin-on techniques. Spin-on deposition of conformal layer  40  may be beneficial when recording patterns having numerous features per unit area, i.e., a dense featured pattern. 
         [0026]    Referring to  FIGS. 6 and 7 , a blanket etch is employed to remove portions of conformal layer  40  to provide multi-layered structure  38  with a crown surface  38   a.  Crown surface  38   a  is defined by an exposed surface  30   e  of each of protrusions  30   b  and upper surfaces of portions  40   c  that remain on conformal layer  40  after the blanket etch. 
         [0027]    Referring to  FIGS. 7 and 8 , crown surface  38   a  is subjected to an anisotropic etch. The etch chemistry of the anisotropic etch is selected to maximize etching of protrusions  30   b  and the segments of patterned imprinting layer  34 , shown in  FIG. 6 , in superimposition therewith, while minimizing etching of the portions  40   c  in superimposition with recessions  30   a.  In the present example, advantage was taken of the distinction of the silicon content between the patterned imprinting layer  34  and the conformal layer  40 . Specifically, employing a plasma etch with an oxygen-based chemistry, it was determined that an in-situ hardened mask  42  would be created in the regions of portions  40   c  proximate to surface  38   a.  This results from the interaction of the silicon-containing polymerizable material with the oxygen plasma. As a result of the hardened mask  42  and the anisotropicity of the etch process, regions  44  of wafer  31  in superimposition with protrusions  30   b  are exposed. The width U′ of regions  44  is optimally equal to width W 2 , shown in  FIG. 2 . 
         [0028]    Referring to  FIGS. 2 ,  7  and  8 , the advantages of this process are manifold. For example, the relative etch rate between portions  40   c  and exposed surfaces  30   e  may be in a range of about 1.5:1 to about 100:1 due to the presence of the hardened mask  42 . As a result, the dimensional width U′ of regions  44  may be precisely controlled, thereby reducing transfer distortions of the pattern into wafer  31 . 
         [0029]    Referring to  FIGS. 1 ,  5  and  11  additionally, the control of dimensional width U′ becomes relatively independent of residual thickness t 2 . The rate at which the polymerizable fluid fills the pattern on mold  28  is inversely proportional to the cube of residual thickness t 2 . As a result, residual thickness t 2  may be selected to maximize throughput without substantially increasing transfer distortions. Decoupling of the transfer distortions from residual thickness t 2  facilitates patterning non-planar surfaces without exacerbating transfer distortions. This is particularly useful when mold  28  is deformed due to external forces, such as typically occurs when varying the dimensions of mold  28  when effectuating magnification correction. As a result, deformation in mold patterned imprinting layer  34  may have a profile in which apex  130   c  of protrusions  130   b  are not coplanar and/or nadir surface  130   d  of recessions  130   a  are not coplanar. 
         [0030]    To attenuate the transfer distortions that may result from this profile, conformal layer  140  is deposited so that distances, k i , between the apex  130   c  of each of the protrusions  130   b  and normalization surface  140   a  satisfies the following parameter: 
         [0000]      | k   i     min     −k   i     max     −&lt;t   3    
         [0000]    where k i     min    is smallest value for k i  and k i     max    is the greatest value for k i  and t 3  is the height of protrusion  130   b  measured between apex  130   c  and nadir surface  130   d.  Thus, the constraint on the normalization provided by normalization surface  140   a  may be relaxed so as not to require each value of k i  to be substantially identical. To that end, conformal layer  140  may be applied by either spin-coating techniques or imprint lithography techniques. Thereafter, stage  20  is employed to move substrate  131  along the Z-axis to compress conformal layer  140  against a planar surface, such as mold  28 . Alternatively, mold  28  may be moved against normalization surface  140   a  or both. 
         [0031]    Finally, forming patterned imprinting layer  34  from a substantially silicon-free polymerizable fluid eases the cleaning process of mold  28 , especially considering that mold  28  is often formed from fused silica. 
         [0032]    Referring to both  FIGS. 1 and 2 , 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 patterned imprinting layer  34  is known to one skilled in the art and typically depends on the specific application which is desired. Furthermore, the plurality of features on patterned mold  28  are shown as recesses  28   a  extending along a direction parallel to projections  28   b  that provide a cross-section of patterned mold  28  with a shape of a battlement. However, recesses  28   a  and projections  28   b  may correspond to virtually any feature required to create an integrated circuit and may be as small as a few tenths of nanometers. 
         [0033]    It may be desired to manufacture components of system  10  from materials that are thermally stable, e.g., have a thermal expansion coefficient of less than about 10 ppm/degree Centigrade at about room temperature (e.g. 25 degrees Centigrade). In some embodiments, the material of construction may have a thermal expansion coefficient of less than about 10 ppm/degree Centigrade, or less than 1 ppm/degree Centigrade. To that end, bridge supports  12 , bridge  14 , and/or stage support  16  may be fabricated from one or more of the following materials: silicon carbide, iron alloys available under the trade-name INVAR®, or trade-name SUPER INVAR™, ceramics, including but not limited to ZERODUR® ceramic. Additionally, table  24  may be constructed to isolate the remaining components of system  10  from vibrations in the surrounding environment. An exemplary table  24  is available from Newport Corporation of Irvine, Calif. 
         [0034]    Referring to  FIGS. 1 ,  2  and  5 , the pattern produced by the present patterning technique may be transferred into wafer  31  provided features have aspect ratios as great as 30:1. To that end, one embodiment of patterned mold  28  has recesses  28   a  defining an aspect ratio in a range of 1:1 to 10:1. Specifically, projections  28   b  have a width W 1  in a range of about 10 nm to about 5000 μm, and recesses  28   a  have a width W 2  in a range of 10 nm to about 5000 μm. As a result, patterned mold  28  and/or substrate  26 , may be formed from various conventional materials, such as, but not limited to, fused-silica, quartz, silicon, organic polymers, siloxane polymers, borosilicate glass, fluorocarbon polymers, metal, and combinations of the above. 
         [0035]    Referring to  FIGS. 1 ,  2  and  3 , the characteristics of material  36   a  are important to efficiently pattern wafer  31  in light of the unique deposition process employed. As mentioned above, material  36   a  is deposited on wafer  31  as a plurality of discrete and spaced-apart beads  36 . The combined volume of beads  36  is such that the material  36   a  is distributed appropriately over area of surface  32  where patterned imprinting layer  34  is to be formed. As a result, patterned imprinting layer  34  is spread and patterned concurrently, with the pattern being subsequently set by exposure to radiation, such as ultraviolet radiation. As a result of the deposition process it is desired that material  36   a  have certain characteristics to facilitate rapid and even spreading of material  36   a  in beads  36  over surface  32  so that all thicknesses t 1  are substantially uniform and all residual thicknesses t 2  are substantially uniform. 
         [0036]    Referring to  FIGS. 2 and 9 , employing the compositions described above in material  36   a,  shown in  FIG. 3 , to facilitate imprint lithography is achieved by including, on substrate  131 , a primer layer  46 . Primer layer  46  functions, inter alia, to provide a standard interface with patterned imprinting layer  34 , thereby reducing the need to customize each process to the material from which substrate  131  is formed. In addition, primer layer  46  may be formed from an organic material with the same etch characteristics as patterned imprinting layer  34 . Primer layer  46  is fabricated in such a manner so as to possess a continuous, smooth, relatively defect-free surface that may exhibit excellent adhesion to patterned imprinting layer  34 . 
         [0037]    Additionally, to ensure that patterned imprinting layer  34  does not adhere to patterned mold  28 , surface  28   c,  shown in  FIG. 5 , may be treated with a low surface energy coating  48 . As a result, patterned imprinting layer  34  is located between primer layer  46  and coating  48  upon contact of mold  28  with substrate  131 . Coating  48  may be applied using any known process. For example, processing techniques may include chemical vapor deposition method, physical vapor deposition, atomic layer deposition or various other techniques, brazing and the like. In a similar fashion a low surface energy coating  148  may be applied to planarizing mold  128 , shown in  FIG. 10 . Alternatively, release properties of either patterned imprinting layer  34  or conformal layer  140 , shown in  FIG. 11 , may be improved by including, in the material from which the same is fabricated, a compound having low surface energy, referred to as a surfactant. The compound is caused to migrate to a surface of the layer formed therewith to interface with mold  28  using known techniques. Typically, the surfactant has a surface energy associated therewith that is lower than a surface energy of the polymerizable material in the layer. An exemplary material and process by which to form the aforementioned surfactant is discussed by Bender et al. in  Multiple Imprinting In UV - Based Nanoimprint Lithography: Related Material Issues,  Microelectronic Engineering pp. 61-62 (2002). The low surface energy of the surfactant provides the desired release properties to reduce adherence of either imprinting layer  34  or conformal layer  40  to mold  28 . It should be understood that the surfactant may be used in conjunction with, or in lieu of, low surface energy coatings  48  and  148 . 
         [0038]    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. The scope of the invention should, therefore, 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.