Abstract:
A method of retaining a substrate to a wafer chuck. The method features accelerating a portion of the substrate toward the wafer chuck, generating a velocity of travel of the substrate toward the wafer chuck, and reducing the velocity before the substrate reaches the wafer chuck. In this manner, the force of impact of the portion with the wafer chuck is greatly reduced, which is believed to reduce the probability that the structural integrity of the substrate, and layers on the substrate and/or the wafer chuck, are damaged.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional patent application of U.S. patent application Ser. No. 11/047,428, filed Jan. 31, 2005, entitled “Chucking System for Nano-Manufacturing,” naming inventors Daniel A. Babbs, Byung-Jin Choi and Anshuman Cherala; and a divisional patent application of U.S. patent application Ser. No. 11/108,208, filed Apr. 18, 2005 entitled “Methods of Separating a Mold from a Solidified Layer Disposed on &amp; Substrate,” naming inventors Byung-Jin Choi, Anshuman Cherala, Yeong-jun Choi, Mario J. Meissl, Sidlgata V. Sreenivasan, Norman E. Schumaker, Ian M. McMackin and Xiaoming Lu. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided by the terms of N66001-01-1-8964 and N66001-02-C-8011 awarded by the Defense Advanced Research Projects Agency (DARPA). 
    
    
     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 method of retaining a substrate to a wafer chuck for use in imprint lithography processes. 
     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 lithographic processes are described in detail in numerous publications, such as U.S. published patent application 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. published patent application 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. published patent application 2004/0046271 filed as U.S. patent application Ser. No. 10/235,314, 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 U.S. published patent applications includes formation of a relief pattern in a polymerizable layer and transferring a pattern corresponding to the relief pattern into an underlying substrate. 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 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. During separation there is a probability that the substrate, pattern record in the solidified layer and/or the solidified layer may be damaged due to the manner in which the substrate is retained upon a wafer chuck employed to support the same. 
     SUMMARY OF THE INVENTION 
     The present invention is directed towards a method of retaining a substrate to a wafer chuck. The method features accelerating a portion of the substrate toward the wafer chuck, generating a velocity of travel of the substrate toward the wafer chuck; and reducing the velocity before the substrate reaches the wafer chuck. In this manner, the force of impact of the portion with the wafer chuck is greatly reduced, which is believed to reduce the probability that the structural integrity of the substrate, and layers on the substrate and/or the wafer chuck are damaged. These embodiments and others are described more fully below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a template in contact with an imprinting layer, disposed upon a substrate in accordance with the prior art; 
         FIG. 2  is a cross-sectional view of a template undergoing separation from an imprinting layer, disposed upon a substrate, in accordance with one embodiment of the present invention; 
         FIG. 3  is a cross-sectional view of a template undergoing separation from an imprinting layer, disposed upon a substrate, in accordance with a second embodiment of the present invention; 
         FIG. 4  is a cross-sectional view of a template mounted to a template holder in accordance with the present invention; 
         FIG. 5  is a top down view of a wafer chuck demonstrating a first embodiment of differing vacuum sections that may be provided in accordance with the present invention; 
         FIG. 6  is a top down view of a wafer chuck demonstrating a second embodiment of differing vacuum sections that may be provided in accordance with the present invention; 
         FIG. 7  is a top down view of a wafer chuck demonstrating a third embodiment of differing vacuum sections that may be provided in accordance with the present invention; 
         FIG. 8  is a side view of the wafer chuck and substrate shown in  FIG. 3  being subject to a release scheme in accordance with an alternate embodiment; 
         FIG. 9  is a top down view of one embodiment of the wafer chuck shown in  FIG. 2 ; 
         FIG. 10  is a cross-sectional view of the wafer chuck shown in  FIG. 9  taken along lines  10 - 10 ; 
         FIG. 11  is a cross-sectional view of a wafer chuck shown in  FIG. 10  having a substrate disposed thereon; 
         FIG. 12  is a cross-sectional view of a second embodiment of the wafer chuck, shown in  FIG. 2 , having a substrate disposed thereon; 
         FIG. 13  is a cross-sectional view of a template in contact with an imprinting layer, disposed upon a substrate, wherein the substrate is subjected to a pushing force; 
         FIG. 14  is a simplified top down plan view showing a template having a plurality of air nozzles arranged locally to exert a pushing force; 
         FIG. 15  is a simplified top down plan view showing a template having a plurality of air nozzles arranged as an array to exert a pushing force; 
         FIG. 16  is a simplified top down plan view showing a template having a plurality of trenches disposed therein to facilitate release of air located between a template and an imprinting layer; 
         FIG. 17  is a side view of a template shown in  FIG. 16 ; 
         FIG. 18  is a simplified top plan down view showing a template having a plurality of holes disposed therein to facilitate release of air located between a template and an imprinting layer; and 
         FIG. 19  is a side down view of the template shown in  FIG. 17 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , a template  10  is shown in contact with an imprinting layer  12 . Typically, template  10  may be comprised of fused silica and imprinting layer  12  may be formed from any material known in the art. Exemplary compositions for imprinting material  12  are disclosed in U.S. patent application Ser. No. 10/763,885, filed Jan. 24, 2003, entitled Materials and Methods for Imprint Lithography, which is incorporated by reference. Imprinting layer  12  may be positioned on a substrate  14 , with substrate  14  having a thickness ‘t’ associated therewith. Substrate  14  may be formed from virtually any material including silicon, fused silica, metal or compound materials typically associated with the manufacture of integrated circuits. Template  10  comprises a surface  16  having a plurality of features disposed thereon, with the plurality of features comprising a plurality of protrusions  18  and recessions  20 . The plurality of protrusions  18  and recessions  20  form a pattern to be transferred into imprinting layer  12 , forming a relief image therein. More specifically, template  10  contacts imprinting layer  12  such that the material of imprinting layer  12  ingresses into and fills the plurality of recessions  20  to form imprinting layer  12  with a contiguous structure across surface  16  of template  10 , wherein typically the atmosphere surrounding template  10  and imprinting layer  12  may be saturated with helium. Template  10  may be connected to an imprint head  11 . The imprint head  11  may be adapted to move along the X-, Y-, and/or Z-axes, thereby generating separation force F S  by moving template  10  along the Z-axis away from substrate  14 . To that end, substrate  14  typically remains in a fixed position with respect to the Z-axis while imprint head  11  undergoes movement. 
     Imprinting layer  12  may be formed from a photo-sensitive material such that when exposed to an actinic component, the same is polymerized and cross-linked to form a solidified material. The actinic component may include 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. 
     Solidification of imprinting layer  12  occurs after template  10  makes contact therewith and the imprinting layer  12  fills the plurality of recessions  20 . Thereafter, template  10  is separated from imprinting layer  12 . In this manner, the relief image is recorded into imprinting layer  12  with a pattern corresponding to the pattern of template  10 . 
     Separation of template  10  from solidified imprinting layer  12  is achieved by application of a force F s , to template  10 . The separation force F s , is of sufficient magnitude to overcome adhesion forces between template  10  and solidified imprinting layer  12  and the resistance of substrate  14  to strain (deformation). It is believed that deformation of a portion of substrate  14  facilitates separation of template  10  from solidified imprinting layer  12 . Wafer chuck  22  may retain substrate  14  during separation using any number of well known straining forces, F c , e.g., electrostatic forces, magnetic forces, vacuum forces and the like. As a result, the direction of separation force F s  is typically opposite to that of the direction of the straining force F c . Typically, wafer chuck  22  is supported by a stage  23  that facilitates movement along X, Y and/or Z axes. An exemplary imprint lithography system is sold under the tradename IMPRIO™ 100 available from Molecular Imprints, Inc. of Austin, Tex. 
     As shown in  FIG. 1 , a magnitude of the strain (deformation) of substrate  14  is a function of the separation force F s  applied and typically results in the formation of strained region  24  in which substrate  14  is spaced from wafer chuck  22  a distance d. Strained region  24  is typically generated proximate to a region of imprinting layer  12  in contact with template  10 , referred to as the processing region. 
     However, it is desired to minimize the magnitude of the separation force F s  necessary to achieve separation of template  10  and solidified imprinting layer  12 . For example, minimizing the magnitude of the separation force F s  facilitates alignment processes so that template  10  and substrate  14  may be properly aligned, as well as allow an increased ratio of template patterning area versus total template area. Additionally, minimizing the separation force F s  necessary to achieve separation of template  10  and solidified imprinting layer  12  reduces the probability of structural comprise of template  10 , substrate  14 , and solidified imprinting material  12 . 
     Furthermore, deformation of substrate  14  creates potential energy in strained region  24  that is transformed into kinetic energy upon separation of template  10  from solidified imprinting layer  12 . Specifically, after separation of template  10  from solidified imprinting layer  12 , the separation force F s  upon substrate  14  approaches zero. The straining force F c  and the elasticity of the material from which substrate  14  is formed causes strained region  24  to accelerate toward chuck  22 , such that strained region  24  typically collides with wafer chuck  22 . It is believed that the collision of strained region  24  with wafer chuck  22  has the deleterious effect of compromising the structural integrity of substrate  14  and the solidified imprinting layer  12  formed thereon. This makes problematic, inter alia, alignment between substrate  14  and template  10 . 
     Referring to  FIG. 2 , the present invention attenuates, if not prevents, the aforementioned deleterious effects associated with separation of template  10  from solidified imprinting layer  12 . This is achieved by reducing, for a given substrate  14 , template  10 , and solidified imprinting layer  12 , the magnitude of the separation force F s  necessary to achieve separation between template  10  and solidified imprinting layer  12 . To that end, wafer chuck  122  is configured to control a magnitude of the strain (deformation) to which substrate  14  is subjected, particularly during separation. Wafer chuck  122  generates a straining force F c  from a plurality of independently generated forces F 1  and F 2 . This facilitates providing a straining force F c  that may vary in direction and magnitude across substrate  14 . For example, the magnitude of variable forces F 2  may be substantially less than the magnitude of chucking forces F 1 . As a result, when template  10  is subjected to a separation force F s , chucking forces F 1  may be associated with a non-strained region  26  of substrate  14 , and variable forces F 2  may be associated with strained region  24  of substrate  14 . 
     In this example, forces F 1  and F 2  are both along directions substantially opposite to the direction of the separation force F s . Separation force F s  may be generated by movement of an imprinting head  11  to which template is connected, as discussed above with respect to  FIG. 1 . Additionally, wafer chuck  122 , shown in  FIG. 2 , may be supported by a stage  23 , as discussed above with respect to  FIG. 1 . It should be noted, however, that separation force F S  may be generated by keeping the position of template  10  fixed with respect to the Z-axis and moving substrate  14  along the Z-axis away from template  10  employing stage  23 . Alternatively, the separation force FS may result from the combination of moving template  10  and substrate  14  in opposite directions along the Z axis. For purposes of the present discussion, however, the invention is discussed with respect to moving imprint head  11  so that template  10  moves along the Z axis away from substrate  14 , while substrate remains fixed with respect to the Z axis. 
     It should be noted that the magnitude of forces F 1  and F 2  may have virtually any value desired, so long as portions of substrate  14  outside of strained region  24  is retained upon wafer chuck  122  when the same is subjected to separation force F s . For example, variable forces F 2  may have a magnitude approaching zero. As a result of the magnitude of variable forces F 2  being substantially less than the magnitude of chucking forces F 1 , the magnitude of the separation force F s  required to separate template  10  from solidified imprinting layer  12  may be reduced. More specifically, the magnitude of variable forces F 2  are established to facilitate strain (deformation) of a portion of substrate  14  in superimposition with template  14  in response to separation force F S , referred to as strained region  24 . 
     Referring to  FIG. 3 , alternatively, straining force F c  may be varied across substrate  14  such that the direction of variable forces F 2  may be opposite to the direction of chucking forces F 1  and commensurate with the direction of separation force F s . The magnitude of the variable forces F 2  may be the same, greater or less than a magnitude of chucking forces F 1 . In this manner, localized deformation of substrate  14  is facilitated by variable forces F 2  pushing strained region  24  away from wafer chuck  122 . This may or may not be independent of the presence of separation force F S . 
     As mentioned above, in the present example chucking forces F 1  function to hold substrate  14  upon wafer chuck  122  when subjected to separation force F s . As a result of the direction of the variable forces F 2  being substantially the same as the direction of the separation force F s , the magnitude of the separation forces F s  required to separate template  10  from solidified imprinting layer  12  may be reduced. 
     Furthermore, as a result of variable forces F 2  being in a direction substantially the same as the direction of separation force F s , the variable forces F 2  may reduce the impact, if not avoid collision, of strained region  24  with template  10 . More specifically, second variable forces F 2  reduce the velocity, and thus, the kinetic energy of strained region  24  as the same propagates towards wafer chuck  122 , after separation of template  10  from solidified imprinting layer  12 . In this manner, strained region  24  comes to rest against wafer chuck  122  without unduly compromising the structural integrity of the same. 
     After separation of template  10  from solidified imprinting layer  12 , the magnitude and direction of variable forces F 2  may be changed. For example, variable forces F 2  may be provided to have the same magnitude and direction as chucking forces F 1 . Further, the change in magnitude and direction of variable forces F 2  may vary linearly during a period of time such that the magnitude of variable forces F 2  having a direction opposite to chucking forces F 1  approaches zero. Upon reaching zero variable forces F 2  change direction and are slowly increased to be commensurate with the magnitude and direction of chucking forces F 1 . As a result, substrate  14  may be subjected to a gradient of variable forces F 2  that slowly decelerate strained region  24  and gradually increase to fixedly secure substrate  14  to wafer chuck  122 . Therefore, an abrupt deceleration of substrate  14  in response to contact with wafer chuck  122 , i.e., a collision, may be avoided while minimizing the force of impact with wafer chuck  122 . 
     Before separation of template  10  from solidified imprinting layer  12 , the direction of the variable forces F 2  may be substantially the opposite as the direction of separation force F s , as described above with respect to  FIG. 2 . However, upon separation of template  10  from solidified imprinting layer  12 , the direction of variable forces F 2  may be substantially the same as the direction of separation force F s , as described above with respect to  FIG. 3 . 
     Referring to  FIGS. 1 and 4 , to further facilitate the separation of template  10  from imprinting layer  12 , template  10  may be subjected to a bowing force F B . More specifically, bowing force F B  may be applied along a center region  28  of template  10  and along a direction opposite to that of the direction of the separation force F s , shown in  FIG. 1 . The bowing force F B  may be applied in conjunction with, or independent of, varying the magnitude and the direction of the straining forces F c , as discussed above. To that end, template  10  may be attached to a template chuck as disclosed in U.S. patent application Ser. No. 10/999,898, filed Nov. 30, 2004, assigned to the assignee of the present patent application and having Cherala et al. identified as inventors, which is incorporated by reference herein. 
     The template chuck includes a body  31  having a centralized throughway  33 , one side of which is sealed by a fused silicate plate  35  and a gasket  36 . Surrounding throughway  33  is a recess  37  and gaskets  38 . Properly positioning template  10  upon body  31  seals throughway  33  forming a chamber, as well as sealing of recess forming a second chamber surrounding the centralized chamber. The centralized chamber and the second chamber may each be provided with a desired pressurization vis-à-vis passageways  40  and  41 , respectively. By evacuating the second chamber and pressurizing the central chamber, bowing force F B  may be applied to template  10  without removing the same from body  31 . 
     Referring to  FIGS. 1 ,  5  and  6 , to vary the magnitude and the direction of the straining force F c  across substrate  14 , the aforementioned wafer chuck  122  may be employed. Furthermore, the following embodiments may be employed in step and repeat processes, wherein an exemplary step and repeat process is disclosed in United States published patent application No. 2004/0008334 filed as U.S. patent application Ser. No. 10/194,414, assigned to assignee of the present invention and incorporated herein by reference. 
     To that end, wafer chuck  122  may be configured to provide a plurality of discrete vacuum sections  30   A - 30   Z . For purposes of the present invention, each of the plurality of vacuum sections  30   A - 30   Z  is defined as providing one or more chucking forces of common magnitude and direction. e.g., there may be one straining force, F c , associated with one of discrete vacuum sections  30   A - 30   Z  or multiple chucking forces, each of which are substantially identical in direction and magnitude. The number, size and shape of vacuum sections  30   A - 30   Z  may vary dependent upon several factors. Additionally, the size and shape of any one of the plurality of vacuum sections  30   A - 30   Z  may differ from the remaining vacuum sections of the plurality of vacuum sections  30   A - 30   Z . For example, the size and/or shape of one or more of the vacuum sections may be commensurate with the size and/or shape of the region  24 . As a result, each of the plurality of vacuum sections  30   A - 30   Z  may be provided with one of a number of shapes, including any polygonal shape, such as the square shape as shown, as well as circular shapes shown as  130  or annular shapes shown as  230 , in  FIG. 6 . Additionally, vacuum sections may include any one or more of irregular shapes  330 , shown in  FIG. 7 . 
     Referring to  FIGS. 5-7 , although it is possible that each of the plurality of vacuum sections defined on a common wafer chuck  122  have a common shape and size, it is not necessary. Thus wafer chuck  222  may define irregular vacuum sections  330 , along with a hexagonal vacuum section  430 , a rectangular vacuum section  530 , a circular vacuum section  130 , and an annular vacuum section  230 . 
     Referring to  FIGS. 2 ,  5 ,  7  and  8 , each of the plurality of vacuum sections  30   A - 30   Z  may be individually addressed so that differing chucking forces may be associated with the plurality of vacuum sections  30   A - 30   Z . In this manner, the locus of the desired chucking forces, e.g., F 1  and/or F 2 , may be established with great precision. It is desired, however, to vary the straining forces F c  associated with the plurality of vacuum sections  30   A - 30   Z  so that substrate  14  may be along an axis that extends across the entire area of substrate  14 . To that end, adjacent rows of said plurality of vacuum sections  30   A - 30   Z  define a straining force differential ΔF C . For example, vacuum sections  30   D ,  30   I ,  30   O ,  30   U ,  30   Z ,  30   J ,  30   P ,  30   V  may generate variable force F 2 , that is lower than chucking force F 1 , generated by the remaining vacuum sections,  30   A ,  30   B ,  30   C ,  30   E ,  30   P ,  30   G ,  30   H ,  30   K ,  30   L ,  30   M ,  30   N ,  30   Q ,  30   R ,  30   S ,  30   T ,  30   W ,  30   X , and  30   Y . This would enable substrate  14  to bend about axis A, which is facilitated by the force differential ΔF C  being defined between a first row consisting of vacuum sections  30   D ,  30   I ,  30   O ,  30   U  and  30   Z , and a second row consisting of vacuum sections  30   C ,  30   H ,  30   N ,  30   T  and  30   Y . 
     Referring to  FIGS. 9 and 10 , to provide wafer chucks  122  and/or  222  with the aforementioned vacuum characteristics, wafer chuck  122  and  222  are integrally formed from stainless steel or aluminum with a plurality of spaced-apart pins  32  and  33 , defining a plurality of channels  36  therebetween. Although shown as having a circular cross-section, each of the plurality of pins  32  and  33  may have virtually any cross-sectional shape desired, including polygonal shapes and typically have a pitch of 3 millimeters. One or more of the plurality of pins are hollow defining a throughway  34  that extends from a passageway  35 , terminating in an opening facing substrate  14 , as shown in  FIG. 11 . These are shown as pins  32 , with throughway typically having a diameter of approximately 1 millimeter to prevent bowing of the portion of substrate  124  in superimposition therewith. 
     Although each of pins  32  is shown in fluid communication with a common passageway  35 , this is not necessary. Rather, throughway  34  of each of the plurality of pins  32  may be individually addressable such that the volume and direction of fluid passing therethrough per unit time is independent of the fluid flow through throughways  34  associated with the remaining pins  32 . This may be achieved by placing one or more of pins  32  in fluid communication with a passageway that differs from the passageways in fluid communication with the remaining pins  32 . In a further embodiment, throughways  34  may comprise a stepped structure. The plurality of pins  34  may be surrounded by a land  37  upon which substrate  14  rests. Channels  36  are typically in fluid communication with a common passageway  39  via aperture  40 . 
     Referring to  FIGS. 10 and 11 , substrate  14  is retained on wafer chuck  122  by straining force F c  generated by fluid flow through channels  36  and/or throughways  34 . To that end, passageway  35  is in fluid communication with a pressure control system  41  and passageway  39  is in fluid communication with a pressure control system  43 . Both of pressure control systems  41  and  43  are operated under control of processor  45  that is in data communication therewith. To that end, processor may include computer readable code operated on by the processor to carrying out the fluid flows mentioned with respect to  FIGS. 2-11 . Upon being disposed upon wafer chuck  122 , one surface  47  of substrate  14 , facing wafer chuck  122 , rests against pins  32  and  33 . In the presence of the straining force F c , and the absence of separation force F s , an end of throughways  34  facing substrate  14  is substantially sealed, hermetically, by surface  47  resting against pins  32  and  33 . No fluid flows between throughways  34  and channels  36  as a result of the seal by surface  47 . 
     Upon application of separation force F s , a portion of surface  47  in superimposition with solidified imprinting layer  12  becomes separated from pins  32  and/or  33 . To facilitate this separation by reducing a magnitude of separation force F S  required to achieve the same, pins  32  are disposed throughout the area of wafer chuck  122 . The fluid flowing through throughways  34  is selected so that variable force F 2  is less than chucking force F 1 . Typically, chucking force F 1  is generated by operating pressure control system  43  at full vacuum. When variable force F 2  is operated in a pressure state, it is of sufficient magnitude to generate a pressure of approximately 200 kilo Pascals (kPa) in the volume disposed between strained region  24  and wafer chuck  122 . This is usually creates approximately 10 microns of movement of substrate  14  at strained region  24 . As a result of the seal being broken, throughways  34  are placed into fluid communication with passageway  39  via channels  36  and apertures  40 . This further reduces the magnitude of straining forces F C  in superimposition with strained region  24 , thereby reducing the separation force F S  required to separate template  10  from imprinting layer because strain/deformation of substrate  14  in region  24  is facilitated. 
     Referring to  FIG. 12 , in an alternate embodiment, wafer chuck  322  may provide the aforementioned vacuum characteristics, without use of pins  32  and  33 . To that end, a surface  49  of wafer chuck  322  includes a plurality of apertures  50  and  52  that may be configured to have a flow of fluid therethrough, the magnitude and direction of which may be independent of the flow of fluid through the remaining apertures  50  and  52 . Apertures typically have a 3 millimeter pitch and a diameter of 2 millimeters, sufficient to reduce the probability of bowing of the portion of substrate  14  in superimposition therewith. 
     In the present example, apertures  50  are in fluid communication with a common passageway  53  and apertures  52  are in fluid communication with a common passageway  55 . The straining force F c  generated by fluid flows through one or more of the plurality of spaced-apart apertures  50  and  52 . Before separation, the portion of the plurality of spaced-apart apertures  50  and  52  may have fluid passing therethrough at a first flow rate, 0 sccm or greater. Were separation force F s  present, fluid may pass through apertures  50  and  52  at a flow rate that differs from the first flow rate. Specifically, the flow rate of fluid passing through apertures  50  and  52  may vary in response to the presence of separation force F S . Typically the aforementioned change in flow rate is localized to apertures  50  and  52  in superimposition with strained region  24 . The change in flow rate is typically sufficient to reduce the magnitude of the straining force F c . As such, the change in flow rate typically affects the fluid passing though only one of apertures  52  or apertures  50 . For example, the flow rate through apertures  52 , in superimposition with strained region  24 , would change so that the straining force F C  generated thereby is reduced. The flow rate through apertures  50  remains substantially constant. 
     Referring to  FIG. 2 , to further assist in separation of template  10  from imprinting layer  12 , the imprinting layer may be composed of material that produces a gaseous by-product when exposed to predetermined wavelengths as disclosed in U.S. Pat. No. 6,218,316 which is incorporated by reference herein. The gaseous by-product can produce localized pressure at the interface between imprinting layer  12  and mold the flat surface. The localized pressure can facilitate separation of template  10  from imprinting layer  12 . The wavelength of radiation that facilitates generation of the gaseous by-product may include such wavelengths as 157 nm, 248 nm, 257 nm and 308 nm, or a combination thereof. After generation of the gaseous by-product, it is desired to expeditiously commence separation of template  10  so as to minimize damage to imprinting layer  12 . Further, the gaseous by-product located between template  10  and imprinting layer  12  may leak out from between template  10  and imprinting layer  12 , which is undesirable. Furthermore, the separation of template  10  from imprinting layer  12  should be orthogonal to imprinting layer  12  to minimize distortions of the imprinting layer  12 . 
     Referring to  FIG. 13  to further assist in separation of template  10  from imprinting layer  12 , a pushing force F p  may be employed between template  10  and substrate  14 . Specifically, the pushing force F p  may be applied proximate to substrate  14  in areas of substrate  14  not in superimposition with template  10 . The pushing force F p  facilitates in separation of template  10  by moving substrate  14  away from template  10 . To that end, pushing force F P  is directed along a direction opposite to separation force F S ; thereby the magnitude of the separation force F S  required to achieve separation may be reduced. The pushing force F p  may be applied by a plurality of air nozzles  62  arranged locally, as shown in  FIG. 14 , or as an array  162 , as shown in  FIG. 15 . The gas employed within the plurality of air nozzles includes, but is not limited to, nitrogen (N 2 ). The pushing force F p  may be applied independent or in conjunction with varying the straining force F c , as discussed above with respect to  FIGS. 2-12 . 
     Referring to  FIGS. 2 ,  16 , and  17  to further assist in separation of template  10  from imprinting layer  12 , template  10  may comprises a plurality of trenches  38  to decrease the vacuum sealing effect between template  10  and imprinting layer  12 . Trenches  66  facilitate release of air positioned between template  10  and imprinting layer  12  when template  10  and imprinting layer  12  are in contact, thus decreasing the vacuum sealing effect between template  10  and imprinting layer  12 . As a result, the magnitude of the separation force F s  may be reduced, which is desired. 
     Referring to  FIGS. 18 and 19 , in a further embodiment, template  10  may comprise a plurality of holes  68 , wherein the plurality of holes  68  function analogously to trenches  66 , such that holes  68  function to decrease the vacuum sealing effect between template  10  and imprinting layer  12 . 
     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.