Abstract:
The present invention is directed to a method of forming a pattern on a plate employing a mold. The method includes placing the plate in superimposition with said mold. Formable material is positioned between that plate and the mold. A pattern is formed in the formable material having a shape complementary to the shape of the mold, defining patterned material. The patterned material is then adhered to the plate.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The field of invention relates generally to imprint lithography. More particularly, the present invention is directed to a method of forming a template to be used in imprint lithography processes.  
         [0002]     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 higher 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 have been employed include biotechnology, optical technology, mechanical systems and the like.  
         [0003]     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. A template makes mechanical contact with the polymerizable fluid. The template 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 to polymerize the same, forming a solidified polymeric material on the transfer layer that contains a relief structure complimentary to that of the template. The template is then separated from the solid polymeric material such that a replica of the relief structure of the template 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.  
         [0004]     The templates employed in the micro-fabrication described above are typically comprised of fused silica, and as a result, the templates are transparent to actinic radiation employed in the polymerization step of the polymerizable fluid composition described above. However, while fused silica templates can be readily prepared with etch depths of a few hundred nanometers, etching deep structures of the order of a few microns while maintaining vertical sidewalls is much more difficult, and obtaining etch depths on the order of tens of microns is extremely difficult. Using templates of this kind, with deep etched features are very useful when, instead of using solidified materials, as described above, as etch resists, the materials defined are intended to form part of the final device functionality. Examples where such deep etched templates are valuable include, without limitation, the formation of polymeric waveguides, the generation of micro/nano-fluidic channels, or in areas of IC packaging.  
         [0005]     Previous art attempts have employed etching as a means for improving the feature depth of fused silica templates. However, such etching techniques have drawbacks associated therewith. Dry etching of fused silica templates to achieve etch depths of greater than a few microns, e.g. 5 μm, is problematic, and more specifically, achieving vertical sidewalls on features more than a few microns, e.g. 5 μm, in fused silica templates is difficult. Wet etching is capable of creating deep features in fused silica; however, it is not anisotropic enough to be used in this application.  
         [0006]     It is desired, therefore, to provide an improved method of forming a template having deep features formed therein.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention is directed to a method of forming a pattern on a plate by employing a mold. The method includes placing the plate in superimposition with the mold. Formable material is present between the plate and the mold. A pattern is formed in the formable material having a shape complementary to the shape of the mold, defining patterned material. The patterned material is then adhered to the plate. These and other embodiments are described more fully below. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]      FIG. 1  is a perspective view of a lithographic system in accordance with the present invention;  
         [0009]      FIG. 2  is a side view of the backing plate disposed opposite a mold with a pattern of the mold forming a pattern to be transferred to the backing plate;  
         [0010]      FIG. 3  is an exploded view of  FIG. 2  depicting a feature depth of the mold;  
         [0011]      FIG. 4  is a side view of the backing plate disposed opposite the mold with an imprinting layer disposed upon the mold;  
         [0012]      FIG. 5  is a side view of the backing plate in contact with the imprinting layer with a radiation source impinging actinic radiation upon the imprinting layer;  
         [0013]      FIG. 6  is a side view of the backing plate having the imprinting layer disposed thereon and spaced-apart from the mold with a radiation source impinging actinic radiation upon the imprinting layer;  
         [0014]      FIG. 7  is a side view of a template comprising the imprinting layer coupled to the backing plate formed utilizing the method employed in the present invention; and  
         [0015]      FIG. 8  is an exploded view of  FIG. 7  depicting a feature depth of the imprinting layer. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]      FIG. 1  depicts a lithographic system  10  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  and provides movement along the Z-axis. 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. It should be understood that imprint head  18  may provide movement along the X- and Y-axes, as well as the Z-axis, and motion stage  20  may provide movement in the Z-axis, as well as the X- and Y-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  22  is coupled to lithographic 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 . An exemplary lithographic system is available under the trade name IMPRIO 100™ from Molecular Imprints, Inc., having a place of business at 1807-C Braker Lane, Suite 100, Austin, Tex. 78758. The system description for the IMPRIO 100™ is available at www.molecularimprints.com and is incorporated herein by reference.  
         [0017]      FIG. 2  shows a master template  24  spaced apart from a backing plate  26  with a distance “d” defined therebetween, with backing plate  26  being substantially parallel to master template  24 . Master template  24  comprises a mold  28  disposed on a surface  30  of a substrate  32  with surface  30  having a substantially planar surface and mold  28  being substantially parallel to substrate  32 . Substrate  32  is located on a wafer chuck  34  with an exemplary chuck disclosed in U.S. patent application Ser. No. 10/293,224, filed Nov. 13, 2003, entitled “A Chucking System for Modulating Shapes of Substrates,” which is assigned to the assignee of the present invention and is incorporated by reference in its entirety herein.  
         [0018]     Backing plate  26  is formed from a material that is substantially transparent to actinic radiation, e.g., ultraviolet (UV) radiation. In a further embodiment, backing plate  26  is formed from a material that is also substantially transparent to infrared (IR) radiation. To that end, backing plate  26  may be formed from such materials including, but not limited to, quartz, fused silica, and soda lime glass. Backing plate  26  may be coated with a coupling agent  35 , wherein coupling agent  35  is substantially transparent to actinic radiation, e.g., UV radiation. In a further embodiment, coupling agent  35  is also substantially transparent to IR radiation. Coupling agent  35  may be deposited upon backing plate  26  in a plurality of methods including, but not limited to, spin coating and dip coating. Coupling agent  35  may be thermally treated, with such thermal treatment techniques including baking coupling agent  35  at a temperature in the range of 50° C.-150° C. for approximately fifteen minutes. Coupling agent  35  is employed to chemically bond to a layer in contact therewith when exposed to actinic radiation, e.g., UV radiation, described further below. An exemplary embodiment of coupling agent  35  used in the present invention is 3-(trimethoxysilyl)propyl acrylate available from Sigma-Aldrich located in St. Louis, Mo.  
         [0019]     Mold  28  may be formed from any suitable material including materials that are substantially opaque to actinic radiation. Additionally, mold  28  may be formed from materials including, but not limited to, silicon, gallium arsenide, quartz, fused-silica, sapphire, organic polymers, siloxane polymers, borosilicate glass, fluorocarbon polymers or a combination thereof. In an exemplary case, mold  28  is formed from silicon. Mold  28  may be treated with a release layer  36 . Release layer  36  may be formed from materials including, but not limited to, perfluoro silane, diamond-like carbon (DLC), diamond-like nano-composite or a surfactant. An example of a surfactant is disclosed in U.S. patent application Ser. No. 10/463,396, filed Jun. 17, 2003, entitled “Method to Reduce Adhesions Between a Conformable Region and Pattern of a Mold,” which is assigned to the assignee of the present invention and is incorporated by reference in its entirety herein. Release layer  36  may be deposited upon mold  28  before or after mold  28  is coupled to substrate  30  to form master template  24  and may be applied using any known method, with such methods including, but not limited to, chemical vapor deposition, physical vapor deposition, atomic layer deposition or various other techniques, such as dip coating and spin coating and the like.  
         [0020]     Referring to  FIGS. 2 and 3 , mold  28  comprises a relief pattern  38  defined thereon. In an exemplary embodiment of the present invention, relief pattern  38  comprises a plurality of spaced-apart protrusions  40  and recessions  42 , however, any relief pattern may be employed. The plurality of protrusions  40  and recessions  42  defines an original pattern that forms the basis of a pattern to be transferred onto backing plate  26 , described more fully below. Protrusions  40  and recessions  42  have a height ‘h 1 ’ associated therewith, as shown in  FIG. 3 .  
         [0021]     As mentioned above, in an example, mold  28  is formed from silicon. As a result, protrusions  40  and recessions  42  may comprise deep feature depths since anisotropic etching of deep features within silicon is well known. In the present invention, to form such deep feature depths of protrusions  40  and recessions  42 , mold  28  is subjected to a lattice etch. The lattice etch provides a uniform etch of the silicon contained within mold  28  with an etch rate of 3-45 μm/hr. In the present invention, height ‘h 1 ’ of protrusions  40  and recessions  42  may have a value in the range of 5 μm-100 μm; however, smaller values of ‘h 1 ’ may be achieved if desired. In a preferred embodiment, height ‘h 1 ’ had a value of 60 μm.  
         [0022]     By employing mold  28  having deep features of protrusions  40  and recessions  42 , mold  28  may be used to form deep featured structures therefrom, with such structures having a pattern complimentary to relief pattern  38 . The structure formed from mold  28  may then be utilized as a template in subsequent imprint lithography processes, and more specifically, in subsequent patterning of substrates. An exemplary imprint lithography method and system for patterning of substrates is described in U.S. patent application Ser. No. 10/194,410 filed July 2002 entitled “Method and System for Imprint Lithography using an Electric Field,” which is assigned to the assignee of the present invention and is incorporated by reference in its entirety herein.  
         [0023]     Referring to  FIG. 4 , a flowable region, such as an imprinting layer  44 , is disposed on a surface  46  of mold  28 . Imprinting layer  44  may be deposited upon mold  28  in a plurality of methods including, but not limited to, spin coating techniques and discrete fluid dispense techniques. In an exemplary technique of the present invention, imprinting layer  44  is deposited upon mold  28  as a plurality of spaced-apart discrete droplets  48 . In a further embodiment, imprinting layer  44  may be deposited upon backing plate  26  in a plurality of methods including, but not limited to, spin coating techniques, discrete fluid dispense techniques, and as a plurality of spaced-apart droplets. In a further embodiment, imprinting layer  44  may be substantially transparent to actinic radiation. Imprinting layer  44  may comprise a composition selected from, but not limited to, polycarbonate, poly(methylmethacrylate), epoxy, a sol-gel material, and a hybrid sol-gel material. In an example of the present invention, imprinting layer  44  comprises a hybrid sol-gel material, wherein the sol-gel material has both an organic and inorganic composition. An exemplary hybrid sol-gel material used in the present invention is sold under the trade name Ormocer® B59 available from Microresist Technology GmbH located in Berlin, Germany.  
         [0024]     The hybrid sol-gel material of the present invention comprises both inorganic and organic reactive functionality. During exposure of the hybrid sol-gel material to actinic radiation, e.g. UV radiation, described further below, a photoinitiator incorporated into the hybrid sol-gel initiates polymerization of organic functionality causing the hybrid material to solidify. Suitable photoinitiators for such a hybrid sol-gel depend on the reactive organic functionality used include, but not limited to, 1-hydroxycyclohexyl phenyl ketone, 2-chlorothioxanthone, 2-methylthioxanthone, and 2-isopropylthioxanthoney, where the reactive organic functionality is acrylic-ester based, or where the reactive organic functionality is epoxy or vinyl ether based.  
         [0025]     The hybrid sol-gel as described above further contains an inorganic reactive functionality. Following exposure of the hybrid sol-gel material to actinic radiation, e.g. UV radiation, a thermal processing step allows the reactive inorganic functionality to crosslink to form a rigid, glass-like structured material through condensation polymerization, described further below. Such reactions are well known in the art to be possible with such materials including, but not limited to, silicon alkoxides, titanium alkoxides and aluminum alkoxides. Such reactions are enhanced by the presence of an acid. The acid may be, if desired, generated in such materials either during the application of actinic radiation, e.g. UV radiation, by the addition of photo-acid generators of the kind described above, or during the thermal process, described further below, by the use of thermal acid generators.  
         [0026]     The hybrid sol-gel material employed in imprinting layer  44  has many properties associated therewith, with such properties offering advantages employed in the present invention. More specifically, the hybrid sol-gel material has properties, such as that a hard transparent pattern having desired deep features may be produced therefrom without the need to be subjected to high temperature settings. Thus, the hybrid sol-gel material may be formed using prior art techniques comparable to those utilized in connection with forming photresists, and, as a result, mass production of templates comprising the hybrid sol-gel material may be possible, described further below.  
         [0027]     Additionally, the hybrid sol-gel material comprises other such properties to enable a coupling of imprinting layer  44  to backing plate  26 . More specifically, the hybrid sol-gel material comprises a component that is responsive to actinic radiation, e.g., UV radiation, and cross-links in response thereto, forming a chemical bond between the hybrid sol-gel material of imprinting layer  44  and coupling agent  35  disposed on backing plate  26 , described further below.  
         [0028]     Referring to  FIGS. 1 and 5 , backing plate  26  is shown being coupled to motion stage  20 . To that end, imprint head  18  and/or motion stage  20  may reduce distance “d” between master template  24  and backing plate  26  to allow droplets  48  to come into mechanical contact with coupling layer  35  of backing plate  26 , spreading droplets  48  so as to form imprinting layer  44  with a contiguous formation over relief structure  38 , with imprinting layer  44  substantially taking the shape of relief structure  38  and forming a pattern complimentary therefrom. Protrusions  40  of mold  28  form recessions  50  within imprinting layer  44 , and recessions  42  of mold  28  form protrusions  52  within imprinting layer  44 , shown more clearly in  FIG. 6 . In this manner, the features of mold  28  may be transferred onto backing plate  26  through imprinting layer  44 , wherein imprinting layer  44  becomes coupled to backing plate  26  through chemical bonding.  
         [0029]     Before separation of imprinting layer  44  from mold  28 , imprinting layer  44  is subjected to actinic radiation, e.g., UV radiation. The UV radiation induces a chemical reaction between imprinting layer  44  and coupling agent  35  of backing plate  26 , such that the hybrid sol-gel material of imprinting layer  44  becomes chemically bonded to coupling agent  35  when imprinting layer  44  is in contact with coupling agent  35 . Specifically, as mentioned above, the hybrid sol-gel material comprises a component that facilitates solidification of the hybrid sol-gel material in response to actinic radiation. As a result, the hybrid sol-gel material of imprinting layer  44  becomes chemically bonded to coupling agent  35  upon exposure to UV radiation.  
         [0030]     Referring to  FIG. 6 , furthermore, as mentioned above, mold  28  is treated with a release layer  36 , wherein release layer  36  has a desired surface energy to facilitate release of imprinting layer  44  from mold  28  so as to minimize shearing or tearing of imprinting layer  44 . In this fashion, the integrity of the desired pattern formed in imprinting layer  44  is maintained when imprinting layer  44  is separated from mold  28 .  
         [0031]     Referring to  FIGS. 6 and 7 , after impinging UV radiation upon imprinting layer  44 , imprint head  18 , shown in  FIG. 1 , is moved to increase the distance “d” so that master template  24  and backing plate  26  are spaced-apart. As mentioned above, imprinting layer  44  becomes chemically bonded to coupling agent  35  of backing plate  26 . To that end, increasing the distance ‘d’ between master template  24  and backing plate  26  forms a daughter template  54 , shown in  FIG. 7 . Daughter template  54  may subsequently be utilized in imprint lithography processes for patterning of substrates, as described above in the micro-fabrication of Willson et al. Daughter template  54  may be substantially transparent to UV radiation.  
         [0032]     Referring to  FIG. 8 , as mentioned above, protrusions  40  of mold  28  form recessions  52  of imprinting layer  44  and recessions  42  of mold  28  form protrusions  50  of imprinting layer  44 . To that end, protrusions  50  and recessions  52  of imprinting layer  44  have a height ‘h 2 ’ associated therewith. Height ‘h 2 ’ of imprinting layer  44  is substantially the same as height ‘h 1 ’ of mold  28 . As a result, height ‘h 2 ’ of recessions  50  and protrusions  52  may have a value in the range of 10 μm-100 μm; however, smaller values of ‘h 2 ’ may be achieved if desired. In a preferred embodiment, height ‘h 2 ’ had a value of approximately 60 μm.  
         [0033]     Referring to  FIGS. 6 and 7 , after the separation of imprinting layer  44  from mold  28  to form daughter template  54 , daughter template  54  is thermally treating to complete the vitrification of the hybrid sol-gel material within imprinting layer  44 . Furthermore, thermally treating the hybrid sol-gel material within imprinting layer  44  creates a condensation reaction within the hybrid sol-gel material to form a vitrified, glassy material. To that end, such thermal treatment methods include impinging IR radiation that is produced by radiation source  22  upon imprinting layer  44 . The IR radiation produced by radiation source  22  may be transmitted through backing plate  26  and coupling layer  35 . In a further embodiment, the IR radiation produced by radiation source  22  may be impinged directly onto imprinting layer  44  without being transmitted through backing plate  26  and coupling layer  35 . In a further embodiment, microwave radiation may be impinged upon imprinting layer  44 . Other such thermal treatment methods include baking daughter template  54  at a temperature of 150° C. for approximately one to three hours.  
         [0034]     In a further embodiment, a low surface energy layer  56  may be disposed upon imprinting layer  44 . Low surface energy layer  56  has a desired surface energy associated therewith, wherein the desired surface energy minimizes adhesion between daughter template  54  and any substrates in contact therewith. Low surface energy layer  56  may be formed from materials including, but not limited to, a perfluoro silane, diamond-like carbon (DLC), diamond-like nano-composite, or a surfactant containing material. An exemplary low surface energy layer is disclosed in U.S. patent application Ser. No. 10/687,519, filed Oct. 16, 2003, entitled “Low Surface Energy Templates,” which is assigned to the assignee of the present invention and is incorporated by reference in its entirety herein.  
         [0035]     The embodiments of the present invention described above are exemplary. For example, anomalies in processing regions other than film thickness may be determined. As a result, 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.