Abstract:
The present invention comprises a method for applying a liquid, such as imprinting material, to a substrate that features use of an electromagnetic field to rapidly spread the liquid over a desired portion of the substrate, while confining the same to the desired region.

Description:
BACKGROUND OF THE INVENTION 
     The field of the invention relates generally to micro-fabrication of structures. More particularly, the present invention is directed at the filling process of an UV curable liquid in a relief structure defined on a template. 
     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. 
     Optical lithography techniques are currently used in micro-fabrication. However, these methods are potentially reaching their limits in resolution. Sub-micron scale lithography has been a crucial process in the microelectronics industry. The use of sub-micron scale lithography allows manufacturers to meet the increased demand for smaller and more densely packed electronic components on chips. 
     An exemplary micro-fabrication technique is shown in U.S. Pat. No. 6,334,960 to Willson et al. Willson discloses 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. A mold makes mechanical contact with the polymerizable fluid. The mold includes a relief structure, and the polymerizable fluid composition fills the relief structure. The polymerizable fluid composition is then subjected to conditions to solidify and to polymerize the same, forming a solidified polymeric material on the transfer layer that contains a relief structure complimentary to that of the mold. The mold is then separated from the solid polymeric material such that a replica of the relief structure in the mold is formed in the solidified polymeric material. The 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. The time required by this technique is dependent upon, inter alia, the time the polymerizable material takes to fill the relief structure. 
     Thus, there is a need to provide an improved method for the filling of the relief structure with the polymerizable material. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a method for applying a liquid, such as imprinting material, to a substrate that features use of an electric field to rapidly spread the liquid over a desired region of the substrate while confining the same to the desired region. To that end, the method includes disposing the liquid between the substrate and the template; positioning the template proximate to the substrate, the template comprising a first region and a second region, lying outside of the first region; and moving the liquid over an area of the substrate in superposition with the first region by applying an electromagnetic field to the liquid. By employing an EM field to spread and confine a imprinting material to a desired area on a substrate, the time that is required to pattern the imprinting material is substantially reduced. By reducing the aforementioned time, the overall time efficiency of an imprint lithography process is improved. This results in increased throughput in imprint lithography. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a lithographic system; 
         FIG. 2  is a simplified elevation view of a lithographic system shown in  FIG. 1 ; 
         FIG. 3  is a simplified representation of material from which an imprinting layer, shown in  FIG. 2 , is comprised before being polymerized and cross-linked; 
         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; 
         FIG. 5  is a simplified elevation view of an imprint device spaced-apart from the imprinting layer, shown in  FIG. 1 , after patterning of the imprinting layer; 
         FIG. 6  is a top view of a template comprising a template active area; and 
         FIG. 7  is a cross-sectional view of a template comprising a template active area. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Described below is a broad overview of an imprint lithography process.  FIG. 1  depicts a lithographic system  60  in accordance with one embodiment of the present invention that includes a pair of spaced-apart bridge supports  62  having a bridge  64  and a stage support  66  extending therebetween. Bridge  64  and stage support  66  are spaced-apart. Coupled to bridge  64  is an imprint head  68 , which extends from bridge  64  toward stage support  66 . Disposed upon stage support  66  to face imprint head  68  is a motion stage  70 . Motion stage  70  is configured to move with respect to stage support  66  along X-, Y- and/or Z-axes. An exemplary motion stage device is disclosed in U.S. patent application Ser. No. 10/194,414, filed Jul. 11, 2002, entitled “Step and Repeat Imprint Lithography Systems,” assigned to the assignee of the present invention, and which is incorporated by reference herein in its entirety. A radiation source  36  is coupled to lithographic system  60  to impinge actinic radiation upon motion stage  70 . As shown, radiation source  36  is coupled to bridge  64  and includes a power generator  73  connected to radiation source  36 . 
     Referring to both  FIGS. 1 and 2 , connected to imprint head  68  is a template  14  having a template active area  52  thereon. Template active area  52  includes a plurality of features defined by a plurality of spaced-apart protrusions  26  and recesses  28 . The plurality of features defines a relief structure that is to be transferred into a substrate  20  positioned on motion stage  70 . Substrate  20  may comprise a bare wafer or a wafer with one or more layers disposed thereon, such as a planarization layer, as discussed in U.S. patent application Ser. No. 10/318,319, filed Dec. 12, 2002 and entitled “Planarization Composition And Method Patterning A Substrate Using The Same,” which is incorporated by reference in its entirety herein. Imprint head  68  is adapted to move along X-, Y- and/or Z-axes. As a result, by movement of imprint head  68 , motion stage  70  or both, distance “d” between template active area  52  and substrate  20  is varied. In this manner, the features on template active area  52  may be imprinted into a conformable region of substrate  20 , discussed more fully below. Radiation source  36  is located so that template active area  52  is positioned between radiation source  36  and substrate  20 . Thus, template active area  52  is fabricated from material that allows it to be substantially transparent to the radiation produced by radiation source  36 . 
     Referring to both  FIGS. 2 and 3 , a conformable region, such as an imprinting layer  65 , is disposed on a portion of a surface  82  that presents a substantially planar profile. It should be understood that the conformable region may be formed using any known technique to produce conformable material, such as a hot embossing process disclosed in U.S. Pat. No. 5,772,905 to Chou, 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, conformable region consists of imprinting layer  65  being deposited as a plurality of spaced-apart discrete droplets  50  of material  76   a  on substrate  20 , that may be deposited in any pattern desired, e.g., periodic, aperiodic and the like. Further, droplets  50  may have identical volumes and geometries or may have differing volumes and geometries. An exemplary system for depositing droplets  50  is disclosed in U.S. patent application Ser. No. 10/191,749, filed Jul. 9, 2002, entitled “System and Method for Dispensing Liquids,” assigned to the assignee of the present invention, and which is incorporated by reference herein in its entirety. Imprinting layer  65  is formed from material  76   a  that may be selectively polymerized and cross-linked to record the original pattern therein, defining a recorded pattern. Material  76   a  is shown in  FIG. 4  as being cross-linked at points  76   b , forming cross-linked polymer material  76   c.    
     Referring to  FIGS. 2 ,  3  and  5 , the pattern recorded in imprinting layer  65  is produced, in part, by mechanical contact with template active area  52 . To that end, imprint head  68  reduces the distance “d” to allow imprinting layer  65  to come into mechanical contact with template active area  52 , spreading droplets  50  so as to form imprinting layer  65  with a contiguous formation of material  76   a  over surface  82 . In one embodiment, distance “d” is reduced to allow sub-portions  74   a  of imprinting layer  65  to ingress into and fill recesses  28 . 
     To facilitate filling of recesses  28 , material  76   a , typically an organic monomer, is provided with the requisite properties to completely fill recesses  28  while covering surface  82  with a contiguous formation of material  76   a . An exemplary embodiment of material  76   a  is disclosed in U.S. patent application Ser. No. 10/463,396, filed Jun. 16, 2003, and entitled “Method to Reduce Adhesion Between a Conformable Region and a Pattern of a Mold,” which is incorporated by reference in its entirety herein. In the present embodiment, sub-portions  74   b  of imprinting layer  65  in superimposition with protrusions  26  remain after the desired, usually minimum, distance “d” has been reached, leaving sub-portions  74   a  with a thickness t 1  and sub-portions  74   b  with a thickness t 2 . Thicknesses “t 1 ” and “t 2 ” may be any thickness desired, dependent upon the application. Typically, t 1  is selected so as to be no greater than twice the width u of sub-portions  74   a , i.e., t 1 &lt;2u, shown more clearly in  FIG. 5 . Embodiments presented herein provide a method for confining material  76   a  to a desired region on substrate  20 , wherein the desired region is determined to be in superposition with template active region  52 . 
     Referring to  FIGS. 2 ,  3  and  4 , after a desired distance “d” has been reached, radiation source  36  produces actinic radiation that polymerizes and cross-links material  76   a , forming polymer material  76   c  in which a substantial portion thereof is cross-linked. As a result, material  76   a  transforms to polymer material  76   c , which is a solid, forming an imprinting layer  165 , shown in  FIG. 5 . Specifically, polymer material  76   c  is solidified to provide a side  74   c  of imprinting layer  165  with a shape conforming to a shape of a surface  78   c  of template active area  52 , with imprinting layer  165  having protrusions  84  and recesses  86 . After imprinting layer  165  is transformed to consist of polymer material  76   c , shown in  FIG. 4 , imprint head  68 , shown in  FIG. 2 , is moved to increase distance “d” so that template active area  52  and imprinting layer  165  are spaced-apart. 
     Referring to  FIG. 5 , additional processing may be employed to complete the patterning of substrate  20 . For example, substrate  20  and imprinting layer  165  may be etched to transfer the pattern of imprinting layer  165  into substrate  20 , providing a patterned surface (not shown). To facilitate etching, the material from which imprinting layer  165  is formed may be varied to define a relative etch rate with respect to substrate  20 , as desired. 
     To that end, imprinting layer  165  may be provided with an etch differential with respect to photo-resist material (not shown) selectively disposed thereon. The photo-resist material (not shown) may be provided to further pattern imprinting layer  165 , using known techniques. Any etch process may be employed, dependent upon the etch rate desired and the underlying constituents that form substrate  20  and imprinting layer  165 . Exemplary etch processes may include plasma etching, reactive ion etching, chemical wet etching and the like. 
     Referring to both  FIGS. 1 and 2 , an exemplary radiation source  36  may produce ultraviolet radiation; however, any known radiation source may be employed. The selection of radiation employed to initiate the polymerization of the material in imprinting layer  65  is known to one skilled in the art and typically depends on the specific application which is desired. Furthermore, the plurality of features on template active area  52  are shown as recesses  28  extending along a direction parallel to protrusions  26  that provide a cross-section of template active area  52  with a shape of a battlement. However, recesses  28  and protrusions  26  may correspond to virtually any feature required to create an integrated circuit and may be as small as a few tenths of nanometers. 
     Referring to  FIGS. 1 ,  2  and  5 , the pattern produced by the present patterning technique may be transferred into substrate  20  to provide features having aspect ratios as great as 30:1. To that end, one embodiment of template active area  52  has recesses  28  defining an aspect ratio in a range of 1:1 to 10:1. Specifically, protrusions  26  have a width W 1  in a range of about 10 nm to about 5000 μm, and recesses  28  have a width W 2  in a range of 10 nm to about 5000 μm. As a result, template active area  52  and/or template  14 , 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, hardened sapphire and the like. 
     Referring to  FIGS. 3 ,  4  and  5 , an important requirement in obtaining accurate reproduction of template active area  52  in polymer material  76   c  is ensuring that material  76   a  completely spreads over a region of substrate  20  in superimposition with active area  52  in a time efficient manner. To that end, template  14  is configured to apply an electromagnetic field to material  76   a  so that the same may be attracted to a perimeter of a region of substrate  20  in superimposition with active area  52 , while being confined to that region. To that end, template  14  includes a conducting region  18  to facilitate generation of an EM field, shown more clearly in  FIGS. 6 and 7 . 
     Referring to both  FIGS. 6 and 7 , conducting region  18  substantially surrounds a perimeter  16  of template active area  52  of template  14 . Inclusion of conducting region  18  with template  14  facilitates rapid spreading of imprinting material  76   a  over the region of substrate  20  in superimposition with template active area  52  and maintains the absence of material  76   a  in regions of substrate  20  not in superimposition with template active area  52 . This results from the application of a voltage to conducting region  18  which creates an EM field produced. To that end, conducting region  18  is connected to a voltage source (not shown), desired to generate the EM field. 
     Conducting region may be formed from any suitable material, such as Indium Tin Oxide (ITO). ITO is transparent to visible and UV light and may be patterned using high-resolution e-beam lithography. 
     While the invention has been described with references to various illustrative embodiments, the description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.