Patent Abstract:
An apparatus to control displacement of a body spaced-apart from a surface includes a flexure system having a first flexure member defining a first axis of rotation and a second flexure member defining a second axis of rotation. A body is coupled to the flexure system to move about a plurality of axes. An actuation system is coupled to the flexure system to selectively constrain movement of the body along a subset of the plurality of axes.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a divisional patent application of U.S. patent application Ser. No. 09/698,317, filed Oct. 27, 2000 and entitled “High-Precision Orientation Alignment and Gap Control Stage for Imprint Lithography Processes”; U.S. patent application Ser. No. 10/616,799, filed Jul. 10, 2003, entitled “Method of Manufacturing a Vacuum Chuck Used in Imprint Lithography”; U.S. patent application Ser. No. 10/617,321, filed Jul. 10, 2003 and entitled “Method of Separating a Template from a Substrate During Imprint Lithography”; U.S. patent application Ser. No. 10/775,707, filed Feb. 10, 2004, entitled “Apparatus to Orientate a Body with Respect to a Surface”; U.S. patent application Ser. No. 10/785,248, filed Feb. 24, 2004, entitled “Method to Control the Relative Position Between a Body and a Substrate”; U.S. patent application Ser. No. 10/788,685, filed Feb. 27, 2004, entitled “Method of Orientating a Template with Respect to a Substrate in Response to a Force Exerted on the Template”; U.S. patent application Ser. No. 10/806,956, filed Mar. 23, 2004, entitled “Apparatus to Control Displacement of a Body Spaced-Apart from a Surface,” all having Byung J. Choi, Sidlgata V. Sreenivasan, and Steven C. Johnson listed as inventors, and all of the aforementioned patent applications being incorporated herein by reference.  
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     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 for by the terms of N66001-98-1-8914 awarded by the Defense Advanced Research Projects Agency (DARPA). provided for by the terms of N66001-98-1-8914 awarded by the Defense Advanced Research Projects Agency (DARPA). 
     
    
     TECHNICAL FIELD  
       [0003]     The invention relates in general to techniques for small device manufacturing and specifically to a system, processes and related devices for high precision imprint lithography enabling the manufacture of extremely small features on a substrate, such as a semiconductor wafer. More specifically, the invention relates to methods and components for the orientation and the alignment of a template about a substrate, as well as their separation without destruction of imprinted features.  
       BACKGROUND OF THE INVENTION  
       [0004]     Without limiting the invention, its background is described in connection with a process for the manufacture of sub-100 nm devices using imprint lithography. In manufacturing, lithography techniques that are used for large-scale production include photolithography and other application oriented lithography techniques, such as electron beam lithography, ion-beam and x-ray lithography, as examples. Imprint lithography is a type of lithography that differs from these techniques. Recent research has shown that imprint lithography techniques can print features that are smaller than 50 nm. As such, imprint lithography has the potential to replace photolithography as the choice for semiconductor manufacturing in the sub-100 nm regime. It can also enable cost effective manufacturing of various kinds of devices, including patterned magnetic media for data storage, micro optical devices, MEMS, biological and chemical devices, X-ray optical devices, etc. Current research in the area of imprint lithography has revealed a need for devices that can perform orientation alignment motions between a template, which contains the imprint image, and a substrate, which receives the image. Of critical importance is the careful and precise control of the gap between the template and the substrate. To be successful, the gap may need to be controlled within a few nanometers across the imprinting area, while, at the same time, relative lateral motions between the template and the substrate must be eliminated. This absence of relative motion leads is also preferred since it allows for a complete separation of the gap control problem from the overlay alignment problem.  
         [0005]     For the specific purpose of imprinting, it is necessary to maintain two flat surfaces as close to each other as possible and nearly parallel. This requirement is very stringent as compared to other proximity lithography techniques. Specifically, an average gap of about 100 nm with a variation of less than 50 nm across the imprinted area is required for the imprint process to be successful at sub-100 nm scales. For features that are larger, such as, for example, MEMS or micro optical devices, the requirement is less stringent. Since imprint processes inevitably involve forces between the template and the wafer, it is also desirable to maintain the wafer surface as stationary as possible during imprinting and separation processes. Overlay alignment is required to accurately align two adjacent layers of a device that includes multiple lithographically fabricated layers. Wafer motion in the x-y plane can cause loss of registration for overlay alignment. Prior art references related to orientation and motion control include U.S. Pat. No. 4,098,001, entitled “Remote Center Compliance System;” U.S. Pat. No. 4,202,107, entitled “Remote Axis Admittance System,” both by Paul C. Watson; and U.S. Pat. No. 4,355,469 entitled “Folded Remote Center Compliant Device” by James L. Nevins and Joseph Padavano. These patents relate to fine decoupled orientation stages suitable for aiding insertion and mating maneuvers in robotic machines and docking and assembly equipment. The similarity between these prior art patents and the present invention is in the provision for deformable components that generate rotational motion about a remote center. Such rotational motion is generated, for example, via deformations of three cylindrical components that connect an operator and a subject in parallel. The prior art patents do not, however, disclose designs with the necessary high stiffness to avoid lateral and twisting motions. In fact, such lateral motion is desirable in automated assembly to overcome mis-alignments during the assembly process. Such motion is highly undesirable in imprint lithography since it leads to unwanted overlay errors and could lead to shearing of fabricated structures. Therefore, the kinematic requirements of automated assembly are distinct from the requirements of high precision imprint lithography. The design shown in U.S. Pat. No. 4,355,469 is intended to accommodate larger lateral and rotational error than the designs shown in the first two patents, but this design does not have the capability to constrain undesirable lateral and twisting motions for imprint lithography.  
         [0006]     Another prior art method is disclosed in U.S. Pat. No. 5,772,905 (the &#39;905 patent) by Stephen Y. Chou, which describes a lithographic method and apparatus for creating ultra-fine (sub-25 nm) patterns in a thin film coated on a substrate in which a mold having at least one protruding feature is pressed into a thin film carried on a substrate. The protruding feature in the mold creates a recess of the thin film. First, the mold is removed from the film. The thin film is then processed such that the thin film in the recess is removed exposing the underlying substrate. Thus, the patterns in the mold are replaced in the thin film, completing the lithography. The patterns in the thin film will be, in subsequent processes, reproduced in the substrate or in another material which is added onto the substrate.  
         [0007]     The process of the &#39;905 patent involves the use of high pressures and high temperatures to emboss features on a material using micro molding. The use of high temperatures and pressures, however, is undesirable in imprint lithography since they result in unwanted stresses being placed on the device. For example, high temperatures cause variations in the expansion of the template and the substrate. Since the template and the substrate are often made of different materials, expansion creates serious layer-to-layer alignment problems. To avoid differences in expansion, the same material can be used but this limits material choices and increases overall costs of fabrication. Ideally, imprint lithography could be carried out at room temperatures and low pressures.  
         [0008]     Moreover, the &#39;905 patent provides no details relative to the actual apparatus or equipment that would be used to achieve the process. In order to implement any imprint lithography process in a production setting, a carefully designed system must be utilized. Thus, a machine that can provide robust operation in a production setting is required. The &#39;905 patent does not teach, suggest or disclose such a system or a machine.  
         [0009]     Another issue relates to separation of the template from the substrate following imprinting. Typically, due to the nearly uniform contact area at the template-to-substrate interface, a large separation force is needed to pull the layers apart. Such force, however, could lead to shearing and/or destruction of the features imprinted on the substrate, resulting in decreased yields.  
         [0010]     In short, currently available orientation and overlay alignment methods are unsuitable for use with imprint lithography. A coupling between desirable orientation alignment and undesirable lateral motions can lead to repeated costly overlay alignment errors whenever orientation adjustments are required prior to printing of a field (a field could be for example a 1″ by 1″ region of an 8″ wafer).  
         [0011]     Further development of precise stages for robust implementation of imprint lithography is required for large-scale imprint lithography manufacturing. As such, a need exists for an improved imprint lithography process. A way of using imprint lithography as a fabrication technique without high pressures and high temperatures would provide numerous advantages.  
       SUMMARY OF THE INVENTION  
       [0012]     An apparatus to control displacement of a body spaced-apart from a surface features an actuation system coupled to a flexure system to selectively constrain movement of a body coupled to the flexure system along a subset of the plurality of axes. In this manner, unwanted movement of the body may be constrained to facilitate improved imprinting techniques. To that end, the apparatus includes a first flexure member defining a first axis of rotation and a second flexure member defining a second axis of rotation. The first and the second flexure members are included in the flexure system. The body is coupled to the flexure system to move about a plurality of axes. The actuation system is coupled to the flexure system. In one embodiment, the actuation system provides resistance to translational displacement of said body with respect to a said subset of axes, while allowing free translation displacement with respect to axes outside of said subset, and resistance to rotational displacement of said body with respect to a subgroup of the plurality of axes, while allowing free rotational displacement of said body with respect to axes outside of said subgroup. To that end, the actuation system may include one or more piezo actuators. These and other embodiments are discussed more fully below. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     The above objects and advantages, as well as specific embodiments, are better understood by reference to the following detailed description taken in conjunction with the appended drawings in which:  
         [0014]      FIGS. 1A and 1B  show undesirable gap between a template and a substrate;  
         [0015]      FIGS. 2A through 2E  illustrate a version of the imprint lithography process according to the invention;  
         [0016]      FIG. 3  is a process flow diagram showing the sequence of steps of the imprint lithography process of  FIGS. 2A through 2E ;  
         [0017]      FIG. 4  shows an assembly of an orientation alignment and a gap control system, including both a course calibration stage and a fine orientation alignment and a gap control stage according to one embodiment of the invention;  
         [0018]      FIG. 5  is an exploded view of the system of  FIG. 4 ;  
         [0019]      FIGS. 6A and 6B  show first and second orientation sub-stages, respectively, in the form of first and second flexure members with flexure joints according to one embodiment of the invention;  
         [0020]      FIG. 7  shows the assembled fine orientation stage with first and second flexure members coupled to each other so that their orientation axes converge on a single pivot point;  
         [0021]      FIG. 8  is an assembly view of the course calibration stage (or pre-calibration stage) coupled to the fine orientation stage according to one embodiment;  
         [0022]      FIG. 9  is a simplified diagram of a 4-bar linkage illustrating the motion of flexure joints that results in an orientation axis;  
         [0023]      FIG. 10  illustrates a side view of the assembled orientation stage with piezo actuators;  
         [0024]      FIGS. 11A and 11B  illustrate configurations for a vacuum chuck according to the invention;  
         [0025]      FIG. 12  illustrates the method for manufacturing a vacuum chuck of the types illustrated in  FIGS. 11A and 11B ;  
         [0026]      FIGS. 13A through 13C  illustrate use of the fine orientation stage to separate a template from a substrate using the “peel-and-pull” method of the present invention; and  
         [0027]      FIGS. 14A through 14C  illustrate an alternative method of separating a template from a substrate using a piezo actuator. 
     
    
       [0028]     References in the figures correspond to those in the detailed description unless otherwise indicated.  
       DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0029]     Without limiting the invention, it is herein described in connection with a system, devices, and related processes for imprinting very small features (sub-100 nanometer (nm) range) on a substrate, such as a semiconductor wafer, using methods of imprint lithography. It should be understood that the present invention can have application to other tasks, such as, for example, the manufacture of cost-effective Micro-Electro-Mechanical Systems (or MEMS), as well as various kinds of devices, including patterned magnetic media for data storage, micro optical devices, biological and chemical devices, X-ray optical devices, etc.  
         [0030]     With reference now to the figures and specifically to  FIGS. 1A and 1B , therein are shown arrangements of a template  12  predisposed with respect to a substrate  20  upon which desired features are to be imprinted using imprint lithography. Specifically, template  12  includes a surface  14  that has been fabricated to take on the shape of desired features which, in turn, are transferred to substrate  20 . Between substrate  20  and template  12  lies a transfer layer  18 , which receives the desired features from template  12  via an imprinted layer  16 . As is well known in the art, transfer layer  18  allows one to obtain high aspect ratio structures (or features) from low aspect ratio imprinted features.  
         [0031]     In  FIG. 1A , a wedge-shaped imprinted layer  16  results so that template  12  is closer to substrate  20  at one end of imprinted layer  16 .  FIG. 1B  shows imprinted layer  16  being too thick. Both of these conditions are highly undesirable. The present invention provides a system, processes and related devices for eliminating the conditions illustrated in  FIGS. 1A and 1B , as well as other orientation problems associated with prior art lithography techniques.  
         [0032]     Specifically, for the purpose of imprint lithography, it is necessary to maintain template  12  and substrate  20  as close to each other as possible and nearly parallel. This requirement is very stringent as compared to other proximity lithography techniques, such as proximity printing, contact printing, and X-ray lithography, as examples. Thus, for example, for features that are 100 nm wide and 100 nm deep, an average gap of about 200 nm or less with a variation of less than 50 nm across the imprinting area of substrate  20  is required for the imprint lithography process to be successful. The present invention provides a way of controlling the spacing between template  12  and substrate  20  for successful imprint lithography given such tight and precise gap requirements.  
         [0033]      FIGS. 2A through 2E  illustrate the process, denoted generally as  30 , of imprint lithography according to the invention. In  FIG. 2A , template  12  is orientated in spaced relation to substrate  20  so that a gap  31  is formed in the space separating template  12  and substrate  20 . Surface  14  of template  12  is treated with a thin layer  13  to lower the template surface energy and to assist in separation of template  12  from substrate  20 . The manner of orientation including devices for controlling gap  31  between template  12  and substrate  20  is discussed below. Next, in  FIG. 2B , gap  31  is filled with a substance  40  that conforms to the shape of the treated surface  14 . Essentially, substance  40  forms imprinted layer  16  shown in  FIGS. 1A and 1B . Preferably, substance  40  is a liquid so that it fills the space of gap  31  rather easily without the use of high temperatures and gap  31  can be closed without requiring high pressures.  
         [0034]     A curing agent  32 , shown in  FIG. 2C , is applied to template  12  causing substance  40  to harden and to assume the shape of the space defined by gap  31  between template  12  and substrate  20 . In this way, desired features  44 , shown in  FIG. 2D , from template  12  are transferred to the upper surface of substrate  20 . Transfer layer  18  is provided directly on the upper surface of substrate  20  which facilitates the amplification of features transferred from template  12  onto substrate  20  to generate high aspect ratio features.  
         [0035]     In  FIG. 2D , template  12  is removed from substrate  20 , leaving the desired features  44  thereon. The separation of template  12  from substrate  20  must be done so that desired features  44  remain intact without shearing or tearing from the surface of substrate  20 . The present invention provides a method and an associated system for peeling and pulling (referred to herein as the “peel-and-pull” method) template  12  from substrate  20  following imprinting so the desired features  44  remain intact.  
         [0036]     Finally, in  FIG. 2E , features  44  transferred from template  12 , shown in  FIG. 2D , to substrate  20  are amplified in vertical size by the action of transfer layer  18 , as is known in the use of bi-layer resist processes. The resulting structure can be further processed to complete the manufacturing process using well-known techniques.  FIG. 3  summarizes the imprint lithography process, denoted generally as  50 , of the present invention in flow chart form. Initially, at step  52 , course orientation of a template and a substrate is performed so that a rough alignment of the template and the substrate is achieved. The advantage of course orientation at step  52  is that it allows pre-calibration in a manufacturing environment where numerous devices are to be manufactured with efficiency and with high production yields. For example, where the substrate comprises one of many die on a semiconductor wafer, course alignment (step  52 ) can be performed once on the first die and applied to all other dies during a single production run. In this way, production cycle times are reduced and yields are increased.  
         [0037]     Next, at step  54 , the spacing between the template and the substrate is controlled so that a relatively uniform gap is created between the two layers permitting the type of precise orientation required for successful imprinting. The present invention provides a device and a system for achieving the type of orientation (both course and fine) required at step  54 . At step  56 , a liquid is dispensed into the gap between the template and the substrate. Preferably, the liquid is a UV curable organosilicon solution or other organic liquids that become a solid when exposed to UV light. The fact that a liquid is used eliminates the need for high temperatures and high pressures associated with prior art lithography techniques.  
         [0038]     At step  58 , the gap is closed with fine orientation of the template about the substrate and the liquid is cured resulting in a hardening of the liquid into a form having the features of the template. Next, the template is separated from the substrate, step  60 , resulting in features from the template being imprinted or transferred onto the substrate. Finally, the structure is etched, step  62 , using a preliminary etch to remove residual material and a well-known oxygen etching technique is used to etch the transfer layer.  
         [0039]     As discussed above, requirements for successful imprint lithography include precise alignment and orientation of the template with respect to the substrate to control the gap in between the template and the substrate. The present invention provides a system capable of achieving precise alignment and gap control in a production style fabrication process. Essentially, the system of the present invention provides a pre-calibration stage for performing a preliminary and a course alignment operation between the template and the substrate surface to bring the relative alignment to within the motion range of a fine movement orientation stage. This pre-calibration stage is required only when a new template is installed into the machine (also sometimes known as a stepper) and consists of a base plate, a flexure component, and three micrometers or higher resolution actuators that interconnect the base plate and the flexure component.  
         [0040]     With reference to  FIG. 4 , therein is shown an assembly of the system, denoted generally as  100 , for calibrating and orienting a template, such as template  12 , shown in  FIG. 1A , about a substrate to be imprinted, such as substrate  20 . System  100  can be utilized in a machine, such as a stepper, for mass fabrication of devices in a production type environment using the imprint lithography processes of the present invention. As shown, system  100  is mounted to a top frame  110  which provides support for a housing  120  which contains the pre-calibration stage for course alignment of a template  150  about a substrate (not shown in  FIG. 4 ).  
         [0041]     Housing  120  is seen coupled to a middle frame  114  with guide shafts  112   a  and  112   b  attached to middle frame  114  opposite housing  120 . In one embodiment, three (3) guide shafts are used (the back guide shaft is not visible in  FIG. 4 ) to provide a support for housing  120  as it slides up and down during vertical translation of template  150 . This up-and-down motion of housing  120  is facilitated by sliders  116   a  and  116   b  which attach to corresponding guide shafts  112   a  and  112   b  about middle frame  114 .  
         [0042]     System  100  includes a disk-shaped base plate  122  attached to the bottom portion of housing  120  which, in turn, is coupled to a disk-shaped flexure ring  124  for supporting the lower placed orientation stage comprised of first flexure member  126  and second flexure member  128 . The operation and the configuration of flexure members  126  and  128  are discussed in detail below. In  FIG. 5 , second flexure member  128  is seen to include a template support  130 , which holds template  150  in place during the imprinting process. Typically, template  150  comprises a piece of quartz with desired features imprinted on it, although other template substances may be used according to well-known methods.  
         [0043]     As shown in  FIG. 5 , three (3) actuators  134   a ,  134   b  and  134   c  are fixed within housing  120  and are operably coupled to base plate  122  and flexure ring  124 . In operation, actuators  134   a ,  134   b  and  134   c  would be controlled such that motion of flexure ring  124  is achieved. This allows for coarse pre-calibration. Actuators  134   a ,  134   b  and  134   c  can also be high resolution actuators which are equally spaced-apart about housing  120  permitting the additional functionality of very precise translation of flexure ring  124  in the vertical direction to control the gap accurately. In this way, system  100 , shown in  FIG. 4 , is capable of achieving coarse orientation alignment and precise gap control of template  150  with respect to a substrate to be imprinted.  
         [0044]     System  100  of the present invention provides a mechanism that enables precise control of template  150  so that precise orientation alignment is achieved and a uniform gap is maintained by the template with respect to a substrate surface. Additionally, system  100  provides a way of separating template  150  from the surface of the substrate following imprinting without shearing of features from the substrate surface. The precise alignment, the gap control and the separation features of the present invention are facilitated mainly by the configuration of first and second flexure members  126  and  128 , respectively.  
         [0045]     With reference to  FIGS. 6A and 6B , therein are shown first and second flexure members  126  and  128 , respectively, in more detail. Specifically, first flexure member  126  is seen to include a plurality of flexure joints  160  coupled to corresponding rigid bodies  164  and  166  which form part of arms  172  and  174  extending from a flexure frame  170 . Flexure frame  170  has an opening  182 , which permits the penetration of a curing agent, such as UV light, to reach template  150 , shown in  FIG. 5 , when held in template support  130 . As shown, four (4) flexure joints  160  provide motion of flexure member  126  about a first orientation axis  180 . Flexure frame  170  of first flexure member  126  provides a coupling mechanism for joining with second flexure member  128 , as illustrated in  FIG. 7 .  
         [0046]     Likewise, second flexure member  128 , shown in  FIG. 6B , includes a pair of arms  202  and  204  extending from a frame  206  and including flexure joints  162  and corresponding rigid bodies  208  and  210  which are adapted to cause motion of flexure member  128  about a second orientation axis  200 . Template support  130  is integrated with frame  206  of second flexure member  128  and, like frame  170 , shown in  FIG. 6A , has an opening  212  permitting a curing agent to reach template  150 , shown in  FIG. 5 , when held by template support  130 .  
         [0047]     In operation, first flexure member  126  and second flexure member  128  are joined, as shown in  FIG. 7 , to form the orientation stage  250  of the present invention. Braces  220  and  222  are provided in order to facilitate joining of the two pieces such that first orientation axis  180 , shown in  FIG. 6A , and second orientation axis  200 , shown in  FIG. 6B , are orthogonal to each other and intersect at a pivot point  252  at the template-substrate interface  254 . The fact that first orientation axis  180  and second orientation axis  200  are orthogonal and lie on interface  254  provide the fine alignment and the gap control advantages of the invention. Specifically, with this arrangement, a decoupling of orientation alignment from layer-to-layer overlay alignment is achieved. Furthermore, as explained below, the relative position of first orientation axis  180  and second orientation axis  200  provides orientation stage  250  that can be used to separate template  150  from a substrate without shearing of desired features so that features transferred from template  150  remain intact on the substrate.  
         [0048]     Referring to  FIGS. 6A, 6B  and  7 , flexure joints  160  and  162  are notch-shaped to provide motion of rigid bodies  164 ,  166 ,  208  and  210  about pivot axes that are located along the thinnest cross section of the notches. This configuration provides two (2) flexure-based sub-systems for a fine decoupled orientation stage  250  having decoupled compliant orientation axes  180  and  200 . The two flexure members  126  and  128  are assembled via mating of surfaces such that motion of template  150  occurs about pivot point  252  eliminating “swinging” and other motions that would destroy or shear imprinted features from the substrate. Thus, the fact that orientation stage  250  can precisely move template  150  about pivot point  252  eliminates shearing of desired features from a substrate following imprint lithography.  
         [0049]     A system, like system  100 , shown in  FIG. 4 , based on the concept of the flexure components has been developed for the imprinting process described above in connection with  FIGS. 2A through 2E . One of many potential application areas is the gap control and the overlay alignment required in high-resolution semiconductor manufacturing. Another application may be in the area of single layer imprint lithography for next generation hard disk manufacturing. Several companies are considering such an approach to generate sub-100 nm dots on circular magnetic media. Accordingly, the invention is potentially useful in cost effective commercial fabrication of semiconductor devices and other various kinds of devices, including patterned magnetic media for data storage, micro optical devices, MEMS, biological and chemical devices, X-ray optical devices, etc.  
         [0050]     Referring to  FIG. 8 , during operation of system  100 , shown in  FIG. 4 , a Z-translation stage (not shown) controls the distance between template  150  and the substrate without providing orientation alignment. A pre-calibration stage  260  performs a preliminary alignment operation between template  150  and the wafer surfaces to bring the relative alignment to within the motion range limits of orientation stage  250 , shown in  FIG. 7 . Pre-calibration is required only when a new template is installed into the machine.  
         [0051]     Pre-calibration stage  260  is made of base plate  122 , flexure ring  124 , and actuators  134   a ,  134   b  and  134   c  (collectively  134 ) that interconnect base plate  122  and flexure ring  124  via load cells  270  that measure the imprinting and the separation forces in the Z-direction. Actuators  134   a ,  134   b  and  134   c  can be three differential micrometers capable of expanding and contracting to cause motion of base plate  122  and flexure ring  124 . Alternatively, actuators  134  can be a combination of micrometer and piezo or tip-type piezo actuators, such as those offered by Physik Instruments, Inc.  
         [0052]     Pre-calibration of template  150  with respect to a substrate can be performed by adjusting actuators  134 , while visually inspecting the monochromatic light induced fringe pattern appearing at the interface of the template lower surface and the substrate top surface. Using differential micrometers, it has been demonstrated that two flat surfaces can be oriented parallel within 200 nm error across 1 inch using fringes obtained from green light.  
         [0053]     With reference to  FIG. 9 , therein is shown a flexure model, denoted generally as  300 , useful in understanding the principles of operation for a fine decoupled orientation stage, such as orientation stage  250  of  FIG. 7 . Flexure model  300  includes four (4) parallel joints—Joints  1 ,  2 ,  3  and  4 —that provide a four-bar-linkage system in its nominal and rotated configurations. The angles α 1  and α 2  between the line  310  passing through Joints  1  and  2  and the line  312  passing through Joints  3  and  4 , respectively, are selected so that the compliant alignment axis lies exactly on the template-wafer interface  254  within high precision machining tolerances (a few microns). For fine orientation changes, the rigid body  314  between Joints  2  and  3  rotates about an axis that is depicted by Point C. Rigid body  314  is representative of rigid bodies  164  and  208  of flexure members  126  and  128 , shown in  FIGS. 6A and 6B , respectively.  
         [0054]     Since a similar second flexure component is mounted orthogonally onto the first one, as shown in  FIG. 7 , the resulting orientation stage  250  has two decoupled orientation axes that are orthogonal to each other and lie on template-substrate interface  254 . The flexure components can be readily adapted to have openings so that a curing UV light can pass through template  150  as required in lithographic applications.  
         [0055]     Orientation stage  250  is capable of fine alignment and precise motion of template  150  with respect to a substrate and, as such, is one of the key components of the present invention. The orientation adjustment, which orientation stage  250  provides ideally, leads to negligible lateral motion at the interface and negligible twisting motion about the normal to the interface surface due to selectively constrained high structural stiffness. The second key component of the invention is flexure-based members  126  and  128  with flexure joints  160  and  162  which provide for no particle generation and which can be critical for the success of imprint lithography processes.  
         [0056]     This invention assumes the availability of the absolute gap sensing approach that can measure small gaps of the order of 200 nm or less between template  150  and the substrate with a resolution of a few nanometers. Such gap sensing is required as feedback if gap control is to be actively measured by use of actuators.  
         [0057]      FIG. 10  shows a configuration of orientation stage  250  with piezo actuators, denoted generally as  400 . Configuration  400  generates pure tilting motions with no lateral motions at template-substrate interface  254 , shown in  FIG. 7 . Therefore, a single overlay alignment step will allow the imprinting of a layer on the entire wafer. For overlay alignment, coupled motions between the orientation and the lateral motions lead to inevitable disturbances in X-Y alignment, which requires a complicated field-to-field overlay control loop.  
         [0058]     Preferably, orientation stage  250  possesses high stiffness in the directions where side motions or rotations are undesirable and lower stiffness in directions where necessary orientation motions are desirable, which leads to a selectively compliant device. Therefore, orientation stage  250  can support relatively high loads while achieving proper orientation kinematics between template  150  and the substrate.  
         [0059]     With imprint lithography, a requirement exists that the gap between two extremely flat surfaces be kept uniform. Typically, template  150  is made from optical flat glass using electron beam lithography to ensure that it is substantially flat on the bottom. The wafer substrate, however, can exhibit a “potato chip” effect resulting in small micron-scale variations on its topography. The present invention provides a device, in the form of a vacuum chuck  478 , as shown in  FIG. 12 , to eliminate variations across a surface of the wafer substrate that can occur during imprinting.  
         [0060]     Vacuum chuck  478  serves two primary purposes. First, vacuum chuck  478  is utilized to hold the substrate in place during imprinting and to ensure that the substrate stays flat during the imprinting process. Additionally, vacuum chuck  478  ensures that no particles are present on the back of the substrate during processing. This is important to imprint lithography as particles can create problems that ruin the device and can decrease production yields.  FIGS. 11A and 11B  illustrate variations of a vacuum chuck suitable for these purposes according to two embodiments.  
         [0061]     In  FIG. 11A , a pin-type vacuum chuck  450  is shown as having a large number of pins  452  that eliminates the “potato chip” effect, as well as other deflections, on the substrate during processing. A vacuum channel  454  is provided as a means of pulling on the substrate to keep it in place. The spacing between pins  452  is maintained so the substrate will not bow substantially from the force applied through vacuum channel  454 . At the same time, the tips of pins  452  are small enough to reduce the chance of particles settling on top of them.  
         [0062]     Thus, with pin-type vacuum chuck  450 , a large number of pins  452  are used to avoid local bowing of the substrate. At the same time, the pin heads should be very small since the likelihood of the particle falling in between the gaps between pins  452  can be high, avoiding undesirable changes in the shape of the substrate itself.  
         [0063]      FIG. 11B  shows a groove-type vacuum chuck  460  with grooves  462  across its surface. The multiple grooves  462  perform a similar function to pins  452  of pin-type vacuum chuck  450 , shown in  FIG. 11A . As shown, grooves  462  can take on either a wall shape  464  or have a smooth curved cross section  466 . Cross section  466  of grooves  462  for groove-type vacuum chuck  460  can be adjusted through an etching process. Also, the space and the size of each groove  462  can be as small as hundreds of microns. Vacuum flow to each of grooves  462  can be provided typically through fine vacuum channels across multiple grooves that run in parallel with respect to the chuck surface. The fine vacuum channels can be made along with the grooves through an etching process.  
         [0064]      FIG. 12  illustrates the manufacturing process for both pin-type vacuum chuck  450 , shown in  FIG. 11A , and groove-type vacuum chuck  460 , shown in  FIG. 11B . Using optical flats  470 , no additional grinding and polishing steps are necessary for this process. Drilling at specified places of optical flats  470  produces vacuum flow holes  472  which are then masked and patterned ( 474 ) before etching ( 476 ) to produce the desired feature—either pins or grooves—on the upper surface of optical flat  470 . The surface can then be treated ( 479 ) using well-known methods.  
         [0065]     As discussed above, separation of template  150  from the imprinted layer is a critical and important final step of imprint lithography. Since template  150  and the substrate are almost perfectly oriented, the assembly of template  150 , the imprinted layer, and the substrate leads to a uniform contact between near optical flats, which usually requires a large separation force. In the case of a flexible template or a substrate, the separation can be merely a “peeling process.” However, a flexible template or a substrate is undesirable from the point of view of high-resolution overlay alignment. In the case of quartz template and silicon substrate, the peeling process cannot be implemented easily. The separation of the template from an imprinted layer can be performed successfully either by one of the two following schemes or the combination of them, as illustrated by  FIGS. 13A, 13B  and  13 C.  
         [0066]     For clarity, reference numerals  12 ,  18  and  20  will be used in referring to the template, the transfer layer and the substrate, respectively, in accordance with  FIGS. 1A and 1B . After UV curing of substrate  20 , either template  12  or substrate  20  can be tilted intentionally to induce a wedge  500  between template  12  and transfer layer  18  on which the imprinted layer resides. Orientation stage  250 , shown in  FIG. 10 , of the present invention can be used for this purpose, while substrate  20  is held in place by vacuum chuck  478 , shown in  FIG. 12 . The relative lateral motion between template  12  and substrate  20  can be insignificant during the tilting motion if the tilting axis is located close to the template-substrate interface, shown in  FIG. 7 . Once wedge  500  between template  12  and substrate  20  is large enough, template  12  can be separated from substrate  20  completely using Z-motion. This “peel and pull” method results in the desired features  44 , shown in  FIG. 2E , being left intact on transfer layer  18  and substrate  20  without undesirable shearing.  
         [0067]     An alternative method of separating template  12  from substrate  20  without destroying the desired features  44  is illustrated by  FIGS. 14A, 148  and  14 C. One or more piezo actuators  502  are installed adjacent to template  12 , and a relative tilt can be induced between template  12  and substrate  20 , as shown in  FIG. 14A . The free end of the piezo actuator  502  is in contact with substrate  20  so that when actuator  502  is enlarged, as shown in  FIG. 14B , template  12  can be pushed away from substrate  20 . Combined with a Z-motion between template  12  and substrate  20  ( FIG. 14C ), such a local deformation can induce a “peeling” and “pulling” effect between template  12  and substrate  20 . The free end side of piezo actuator  502  can be surface treated similar to the treatment of the lower surface of template  12  in order to prevent the imprinted layer from sticking to the surface of piezo actuator  502 .  
         [0068]     In summary, the present invention discloses a system, processes and related devices for successful imprint lithography without requiring the use of high temperatures or high pressures. With the present invention, precise control of the gap between a template and a substrate on which desired features from the template are to be transferred is achieved. Moreover, separation of the template from the substrate (and the imprinted layer) is possible without destruction or shearing of desired features. The invention also discloses a way, in the form of suitable vacuum chucks, of holding a substrate in place during imprint lithography.  
         [0069]     While this invention has been described with a reference to 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.

Technology Classification (CPC): 8