Abstract:
The present invention is directed to a method that attenuates, if not avoids, heating of a substrate undergoing imprint lithography process and the deleterious effects associated therewith. To that end, the present invention includes a method of patterning a field of a substrate with a polymeric material that solidifies in response to actinic energy in which a sub-portion of the field is exposed sufficient to cure the polymeric material is said sub-portion followed by a blanket exposure of all of the polymeric material associated with the entire field to cure/solidify the same.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 11/292,402, filed on Nov. 30, 2005 entitled “Method of Exposure for the Purpose of Thermal Management for Imprint Lithography Processes” which claims priority to U.S. Provisional Application No. 60/632,125, filed on Dec. 1, 2004, entitled “Methods of Exposure for the Purpose of Thermal Management for Imprint Lithography Processes,” both of which are incorporated herein by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     The United States government has a paid-up license in this invention and the right in limited circumstance to require the patent owner to license other on reasonable terms as provided by the terms of 70NANB4H3012 awarded by National Institute of Standards (NIST) ATP Award. 
    
    
     BACKGROUND OF THE INVENTION 
     The field of the invention relates generally to nano-fabrication of structures. More particularly, the present invention is directed to a technique to achieve overlay alignment of patterns formed during nano-scale fabrication. 
     Nano-fabrication involves the fabrication of very small structures, e.g., having features on the order of nano-meters 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. 
     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 United States 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”; United States 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. 
     The fundamental imprint lithography technique disclosed in each of the aforementioned United States patent application publications and United States 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. 
     A need exists, therefore, to provide improved alignment techniques for imprint lithographic processes. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a method that attenuates, if not avoids, heating of a substrate undergoing imprint lithography process and the deleterious effects associated therewith. To that end, the present invention includes a method of patterning a field of a substrate with a polymeric material that solidifies in response to actinic energy in which a sub-portion of the field is exposed sufficient to cure the polymeric material in said sub-portion followed by a blanket exposure of all of the polymeric material associated with the entire field to cure/solidify the same. These and other embodiments are discussed below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified plan view of an imprint lithography system having a mold spaced-apart from a substrate; 
         FIG. 2  is a cross-sectional view of a patterned substrate having a plurality of layers disposed thereon with a mold, shown in  FIG. 1 , in superimposition therewith; 
         FIG. 3  is a simplified side view of a portion of the system shown in  FIG. 1 , with the mold in contact with a polymeric layer on the substrate; 
         FIG. 4  is a top-down view of a portion of the substrate shown in  FIG. 1 , the substrate having a plurality of regions associated therewith; 
         FIGS. 5 and 6  are side views of portions of the mold and the polymeric layer, shown in  FIG. 3 , with a portion of the polymeric layer solidified and/or cross-linked; 
         FIG. 7  is a top down view of a polymeric material positioned on the substrate, shown in  FIG. 1 , with an outer region of the polymeric material being solidified and/or cross-linked; 
         FIG. 8  is a top down view of a polymeric material positioned on the substrate, shown in  FIG. 1 , with a grating region of the polymeric material being solidified and/or cross-linked; 
         FIG. 9  is a top down view of a polymeric material positioned on the substrate, shown in  FIG. 1 , with isolated regions of the polymeric material being solidified and/or cross-linked; and 
         FIG. 10  is a top down view of a polymeric material positioned on the substrate, shown in  FIG. 1 , with a scanning beam exposing portions of the polymeric material. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     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 mold  16  with 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. 
     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 . 
     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. 
     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 . 
     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 ultraviolet radiation 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 . Control of this process is regulated by 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 . 
     To allow energy  28  to impinge upon polymeric material  24 , it is desired that mold  16  be substantially transparent to the wavelength of energy  28  so that the same may propagate therethrough. Additionally, to maximize a flux of energy  28  propagating through mold  16 , energy  28  may have a sufficient cross-section to cover the entire area of mold  16  with no obstructions being present in path  30 . 
     Referring to  FIGS. 1 and 2 , often a pattern generated by mold  16  is disposed upon a substrate  112  in which a preexisting pattern in present. To that end, a primer layer  36  is typically deposited upon patterned features, shown as recesses  38  and protrusions  40 , formed into substrate  112  to provide a smooth, if not planar, surface  42  upon which to form a patterned imprint layer (not shown) from polymeric material  24  disposed upon surface  42 . To that end, mold  16  and substrate  112  include alignment marks, which may include sub-portions of the patterned features. For example, mold  16  may have alignment marks, referred to as mold alignment marks, which are defined by features  44  and  46 . Substrate  112  may include alignment marks, referred to as substrate alignment marks, which are defined by features  48  and  50 . 
     To ensure proper alignment between the pattern on substrate  112  with the pattern generated by mold  16 , it is desired to ensure proper alignment between the mold and substrate alignment marks. This has typically been achieved employing the aided eye, e.g., an alignment system  53  selectively placed in optical communication with both mold  16  and substrate  12 , concurrently. Exemplary alignment systems have included ocular microscopes or other imaging systems. Alignment system  53  typically obtains information parallel to path  30 . Alignment is then achieved manually by an operator or automatically using a vision system. 
     Referring to  FIG. 1 , as mentioned above, source  26  produces energy  28  that causes polymeric material  24  to solidify and/or cross-link conforming to the shape of surface  25  of substrate  12  and patterning surface  18 . To that end, often it is desired to complete solidification and/or cross-linking of polymeric material  24  prior to separation of mold  16  from polymeric material  24 . A time required to complete solidification and/or cross-linking of polymeric material  24  may depend upon, inter alia, a magnitude of energy  28  impinging upon polymeric material  24  and chemical and/or optical properties of polymeric material  24  and/or substrate  12 . To that end, in the absence of any amplifying agents, i.e., chemically-amplified photoresist of optical lithography progresses, the magnitude of energy  28  required to solidify and/or cross-link polymeric material  24  may be substantially greater in imprint lithography processes as compared to optical lithography processes. As a result, during solidification and cross-linking of polymeric material  24 , energy  28  may impinge upon substrate  12 , template  14 , and mold  16 , and thus, heat substrate  12 , template  14 , and mold  16 . A substantially uniform magnitude of energy  28  may result in substantially uniform heating of substrate  12 , template  14 , and mold  16 . However, a differential magnitude of energy  28  and/or a differential CTE (coefficient of thermal expansion) associated with substrate  12 , template  14 , and mold  16  may result in misalignment between substrate  12  and mold  16  during solidification and/or cross-linking of polymeric material  24 , which may be undesirable. To that end, a method to minimize, if not prevent, thermal effects upon substrate  12 , template  14 , and mold  16  is described below. 
     Referring to  FIG. 3 , a portion of system  8  is shown. More specifically, patterning surface  18  of mold  16  is shown in contact with polymeric layer  24 . Exposure of an entirety of surface  25  of substrate  12  to energy  28  may increase a temperature thereof, and thus, a linearly increase in size of substrate  12 , which may be undesirable. To that end, a portion of substrate  12  may be exposed to energy  28 , described below. 
     Referring to  FIG. 4 , a portion of substrate  12  is shown having a plurality of regions a-p. As shown, substrate  12  comprises sixteen regions; however, substrate  12  may comprise any number of regions. To that end, to minimize, if not prevent, the aforementioned linearly increase in size of substrate  12 , a subset of the regions a-p of substrate  12  may be exposed to energy  28 , shown in  FIG. 1 . More specifically, regions f, g, j, and k of substrate  12  may be exposed to energy  28 , with regions a-d, e, h, i, and l-p of substrate  12  being substantially absent of exposure to energy  28 . As a result, region a-d, e, h, i, and l-p of substrate  12  may minimize, if not prevent, region f, g, j, and k of substrate  12  from linearly increasing in size, i.e., region a-d, e, h, i, and l-p of substrate  12  may act as a physical constraint to prevent region f, g, j, and k of substrate  12  from increasing in size. Regions f, g, j, and k of substrate  12  may each be exposed to energy  28  sequentially or concurrently. 
     To that end, after exposure of regions f, g, j, and k of substrate  12  to energy  28 , in a first embodiment, regions a-d, e, h, i, and l-p of substrate  12  may be exposed to energy  28  to solidify and/or cross-link the same. In a further embodiment, after exposure of regions f, g, j, and k of substrate  12  to energy  28 , all regions (a-p) of substrate  12  may be exposed to energy  28 , i.e., a blanket exposure to complete solidification and/or cross-linking of polymeric material  24 . 
     Referring to  FIG. 3 , in a further embodiment, it may be desired to expose a portion of substrate  12 , and therefore, polymeric material  24 , to energy  28  such that a position between substrate  12  and mold  16  prior to exposure to energy  28  is substantially the same as a position between substrate  12  and mold  16  subsequent to exposure of energy  28 . More specifically, an interface between substrate  12  and mold  16  via polymeric material  24  may be maintained before and after exposure of substrate  12 , mold  16 , and polymeric material  24  to energy  28 . As a result, an increase in size of substrate  12 , template  14 , and mold  16  resulting from thermal-induced scaling may be minimized, if not prevented. 
     Referring to  FIGS. 3 ,  5 , and  6 , in a first example of the above-mentioned, an outer portion  62  of polymeric material  24  may be exposed to energy  28  prior to inner portion  64  of polymeric material  24 , with outer portion  62  of polymeric material  24  being solidified and/or cross-linked in response to energy  28 . As a result, outer portion  62  may maintain an interface between substrate  12  and mold  18 , and thus, minimize, if not prevent substrate  12  from increasing in size, as desired. In a further embodiment, after exposure of outer portion  62  of polymeric material  24  to energy  28 , inner portion  64  of polymeric material  24  may be subsequently exposed to energy  28  to solidify and/or cross-link the same. In still a further embodiment, after exposure of outer portion  62  of polymeric material  24  to energy  28 , inner and outer portions  62  and  64  of polymeric material  24  may be exposed to energy  28 , i.e., a blanket exposure to complete solidification and/or cross-linking of polymeric material  24 . 
     Referring to  FIGS. 7-9 , further examples are shown of exposing desired regions of polymeric material  24  to minimize, if not prevent, substrate  12  from increasing in size, as desired.  FIG. 7  shows an outer region  66  being exposed to energy  28 , shown in  FIG. 1 , prior to inner region  68  being exposed to energy  28 , shown in  FIG. 1 .  FIG. 8  shows a grating type exposure of polymeric material  24 , with region  70  being exposed to energy  28 , shown in  FIG. 1 , prior to regions  72  being exposed to energy  28 , shown in  FIG. 1 .  FIG. 9  shows an isolated region exposure of polymeric material  24 , with regions  76  being exposed to energy  28 , shown in  FIG. 1 , prior to region  7  is exposed to energy  28 , shown in  FIG. 1 . 
     Referring to  FIG. 1 , energy  28  may have a cross-sectional area associated therewith that may be greater in dimension that a desired region that is to be exposed to energy  28 , i.e. a region a-p of substrate  12 , as shown in  FIG. 4 . To that end, to expose desired regions of substrate  12  to energy  28 , a mask (not shown) may be positioned within path  30  such that energy  28  may propagate therethrough and comprise dimensions commensurate with said desired regions of substrate  12  to expose the same to energy  28 . Further, the mask (not shown) may be removed from path  30  such that substantially all regions of substrate  12  are exposed to energy  28 . In a further embodiment, analogous to the above-mentioned, a first mask (not shown) may be positioned within path  30  such that energy  28  may propagate therethrough to expose a first subset of substrate  12 ; and a second mask (not shown) may be positioned within path  30  such that energy  28  may propagate therethrough to expose a second subset of substrate  12 . 
     Furthermore, as described with respect to  FIG. 4 , a desired subset of the plurality of regions a-p of substrate  12  may be processed to minimize, if not prevent, linearly increasing a size of substrate  12  [hereinafter small field]. However, the above-mentioned methods may be applicable to imprinting of large substrates, i.e., whole wafer imprinting or display substrate imprinting [hereinafter large field]. More specifically, an overlay error associated with large fields may be greater that that as compared to an overlay error associated with small fields; however, an error tolerance associated with the large fields may be comparable or less than that associated with the small fields. In an example of minimizing a size increase of substrate  12  employing imprinting of large substrates, substrate  12  and polymeric material  24  may be exposed to energy  28 , shown in  FIG. 1 , employing a multi-ring type exposure to maintain a desired position between substrate  12  and mold  16 , similar to that as mentioned above with respect to  FIGS. 3 ,  5 , and  6 . Portions of substrate  12  not previously exposed to energy  28 , shown in  FIG. 1 , may be subsequently exposed to energy  28  to complete solidification and/or cross-linking of polymeric material  24 . 
     In a further embodiment, energy  28  may comprise a scanning beam, as shown in  FIG. 10 , such that desired regions of substrate  12  may be exposed to energy  28 . As shown, region  78  of substrate  12  is exposed to energy  28  prior to region  80  of substrate  12  is exposed to energy  28 . In still a further embodiment, contact between mold  16 , shown in  FIG. 1 , and polymeric material  24  and a path of the scanning beam may both travel across substrate  12  and polymeric material  28  in substantially the same direction. 
     Referring to  FIG. 1 , in still a further embodiment, as mentioned above substrate  12  may be coupled to a substrate chuck (not shown). To that end, were the substrate chuck (not shown) able to absorb energy  28 , it may be desired to expose substrate  12  and polymeric material  24  to energy  24  having a reduced magnitude for a longer period of time as compared to the methods mentioned above. As a result, a thermal variation of substrate  12  may be minimized, if not prevented, as desired. 
     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.