Patent Publication Number: US-11034057-B2

Title: Planarization process, apparatus and method of manufacturing an article

Description:
BACKGROUND 
     Field of Art 
     The present disclosure relates to substrate processing, and more particularly, to the planarization of surfaces in semiconductor fabrication. 
     Description of the Related Art 
     Planarization techniques are useful in fabricating semiconductor devices. For example, the process for creating a semiconductor device includes repeatedly adding and removing material to and from a substrate. This process can produce a layered substrate with an irregular height variation (i.e., topography), and as more layers are added, the substrate height variation can increase. The height variation has a negative impact on the ability to add further layers to the layered substrate. Separately, semiconductor substrates (e.g., silicon wafers) themselves are not always perfectly flat and may include an initial surface height variation (i.e., topography). One method of addressing this issue is to planarize the substrate between layering steps. Various lithographic patterning methods benefit from patterning on a planar surface. In ArFi laser-based lithography, planarization improves depth of focus (DOF), critical dimension (CD), and critical dimension uniformity. In extreme ultraviolet lithography (EUV), planarization improves feature placement and DOF. In nanoimprint lithography (NIL) planarization improves feature filling and CD control after pattern transfer. 
     A planarization technique sometimes referred to as inkjet-based adaptive planarization (IAP) involves dispensing a variable drop pattern of polymerizable material between the substrate and a superstrate, where the drop pattern varies depending on the substrate topography. A superstrate is then brought into contact with the polymerizable material after which the material is polymerized on the substrate, and the superstrate removed. Improvements in planarization techniques, including IAP techniques, are desired for improving, e.g., whole wafer processing and semiconductor device fabrication. 
     SUMMARY 
     A method is provided. The method comprises creating at least one crack at a point on an edge of a stack of at least a substrate and a superstrate, propagating the crack along the periphery, and moving the superstrate relative to the substrate to complete separation of the superstrate from the substrate. The method may further comprise introducing a positive fluid pressure between the substrate and the superstrate at the point on the edge to create the crack. The positive fluid pressure includes a flow of clean dry air, helium, or nitrogen. The method may further comprise retaining the superstrate in a superstrate chuck with a negative fluid pressure and applying a high flow of negative fluid pressure to a peripheral zone on the superstrate to propagate the crack along the edge of the stack. 
     The positive fluid pressure is continuously introduced to the separated portion while the high flow of negative fluid pressure is applied to the peripheral zone on the superstrate. The superstrate may be moved in a direction away from the substrate with a superstrate chuck. The method may further comprise applying a negative fluid pressure to a center zone on the superstrate to complete the separation of the superstrate from the substrate with a superstrate chuck. The method may further comprise applying a force at the point on an edge of the superstrate to create the crack. Another crack may be created by applying a positive fluid pressure between the substrate and the superstrate at another point of the edge of the stack. The force may be applied by introducing a positive fluid pressure or a mechanical contact. 
     The method may further comprise stacking the substrate and the superstrate in such a way that the superstrate includes an overhanging edge portion; and applying a force to the overhanging edge portion to create a crack. Another edge portion of the superstrate may be aligned with a notch at an edge portion of the substrate and a force is applied to the another edge portion to create another crack between the substrate and the superstrate. 
     A chucking system is also provided. The system comprises a superstrate chuck configured to retain a superstrate with negative fluid pressure and a source of force configured to apply a force to a point on an edge of the superstrate stacked with a substrate, so as to create a crack between the substrate and the superstrate at the point on the edge. The superstrate chuck includes a pattern of lands, and one of the lands located near an edge of the superstrate chuck is recessed below the other lands located an inner portion of the superstrate chuck to allow the superstrate to deflect towards the superstrate chuck while creating the crack. The chucking system may further comprise a substrate chuck configured to retain the substrate with negative fluid pressure. The substrate chuck includes a pattern of lands, and one of the lands located at an edge of the substrate chuck is recessed below the other lands located at an inner portion of the substrate chuck to allow the substrate to deflect towards the substrate while creating the crack. 
     The source of force includes a mechanism to create a lateral mechanical push or a source of positive fluid pressure towards the edge of the superstrate. The substrate includes a notch arranged at an edge thereof, and the source of force includes a source of negative fluid pressure applied to the superstrate via the notch. The chucking system may further comprise a negative fluid pressure source to apply the negative fluid pressure to the superstrate through the superstrate chuck. The superstrate chuck is configured to retain the superstrate such that the superstrate includes an overhanging portion. The source of force is configured to apply force to the overhanging portion of the superstrate to create the crack. 
     A method of manufacturing an article is provided. The method comprises forming a cured material stacked between a substrate and a superstrate; creating at least one crack at a point at an edge between a substrate and a superstrate; propagating the crack along the periphery; and separating the superstrate from the cured material. 
     These and other objects, features, and advantages of the present disclosure will become apparent upon reading the following detailed description of exemplary embodiments of the present disclosure, when taken in conjunction with the appended drawings, and provided claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       So that features and advantages of the present invention can be understood in detail, a more particular description of embodiments of the invention may be had by reference to the embodiments illustrated in the appended drawings. It is to be noted, however, that the appended drawings only illustrate typical embodiments of the invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  is a diagram illustrating a planarization system; 
         FIGS. 2 a  to 2 c    illustrate a planarization process; 
         FIGS. 3 a  to 3 b    illustrate a multi-zone superstrate chuck in one embodiment; 
         FIGS. 4 a  to 4 e    show the operation of the superstrate chuck for forming a layer on a substrate; 
         FIG. 5  is a flow chart of the planarization process as illustrated in  FIGS. 4 a    to  4   e;    
         FIG. 6 a    shows a separation crack initiated at an edge of a stack of the substrate and the superstrate in one embodiment and  FIG. 6 b    shows the alignment of a retractable pin with a substrate notch for initiation such separation crack; 
         FIG. 6 c    shows a separation crack initiated at an edge of a stack of the substrate and the superstrate in another embodiment; 
         FIGS. 7 a  to 7 c    show the top view of the stack of the substrate and superstrate as a separation crack is initiated and propagated about a periphery of the stack; 
         FIG. 8  shows the separated substrate and superstrate; 
         FIG. 9  is a flow chart of the separation process as illustrated in  FIGS. 7 and 8 ; 
         FIG. 10  shows a separation crack initiated at an edge of a stack of the substrate and the superstrate in a further embodiment; 
         FIGS. 11 a  and 11 b    illustrate a multi-zone superstrate chuck in another embodiment with improved zone sealing; and 
         FIG. 12  shows an enlarged view of an exemplary trench structure within a zone of the  FIGS. 11 a  and 11 b    superstrate chuck. 
     
    
    
     Throughout the figures, the same reference numerals and characters, unless otherwise stated, are used to denote like features, elements, components or portions of the illustrated embodiments. Moreover, while the subject disclosure will now be described in detail with reference to the figures, it is done so in connection with the illustrative exemplary embodiments. It is intended that changes and modifications can be made to the described exemplary embodiments without departing from the true scope and spirit of the subject disclosure as defined by the appended claims. 
     DETAILED DESCRIPTION 
     Planarization System 
       FIG. 1  illustrates a system for planarization. The planarization system  100  is used to planarize a film on a substrate  102 . The substrate  102  may be coupled to a substrate chuck  104 . The substrate chuck  104  may be but is not limited to a vacuum chuck, pin-type chuck, groove-type chuck, electrostatic chuck, electromagnetic chuck, and/or the like. 
     The substrate  102  and the substrate chuck  104  may be further supported by a substrate positioning stage  106 . The substrate positioning stage  106  may provide translational and/or rotational motion along one or more of the x-, y-, z-, θ-, ψ, and φ-axes. The substrate positioning stage  106 , the substrate  102 , and the substrate chuck  104  may also be positioned on a base (not shown). The substrate positioning stage may be a part of a positioning system. 
     Spaced apart from the substrate  102  is a superstrate  108  having a working surface  112  facing substrate  102 . Superstrate  108  may be formed from materials including, but not limited to, fused silica, quartz, silicon, organic polymers, siloxane polymers, borosilicate glass, fluorocarbon polymers, metal, hardened sapphire, and/or the like. In an embodiment the superstrate is readily transparent to UV light. Surface  112  is generally of the same areal size or slightly smaller as the surface of the substrate  108 . 
     Superstrate  108  may be coupled to or retained by a superstrate chuck  118 . The superstrate chuck  118  may be, but is not limited to, vacuum chuck, pin-type chuck, groove-type chuck, electrostatic chuck, electromagnetic chuck, and/or other similar chuck types. The superstrate chuck  118  may be configured to apply stress, pressure, and/or strain to superstrate  108  that varies across the superstrate  108 . In an embodiment the superstrate chuck is likewise readily transparent to UV light. The superstrate chuck  118  may include a system such as a zone based vacuum chuck, an actuator array, a pressure bladder, etc., which can apply a pressure differential to a back surface of the superstrate  108  to cause the template to bend and deform. In one embodiment, the superstrate chuck  118  includes a zone based vacuum chuck which can apply a pressure differential to a back surface of the superstrate, causing the superstrate to bend and deform as further detailed herein. 
     The superstrate chuck  118  may be coupled to a planarization head  120  which is a part of the positioning system. The planarization head  120  may be movably coupled to a bridge. The planarization head  120  may include one or more actuators such as voice coil motors, piezoelectric motors, linear motor, nut and screw motor, etc., which are configured to move the superstrate chuck  118  relative to the substrate  102  in at least the z-axis direction, and potentially other directions (e.g. x-, y-, θ-, ψ-, and φ-axis). 
     The planarization system  100  may further comprise a fluid dispenser  122 . The fluid dispenser  122  may also be movably coupled to the bridge. In an embodiment, the fluid dispenser  122  and the planarization head  120  share one or more of all positioning components. In an alternative embodiment, the fluid dispenser  122  and the planarization head move independently from each other. The fluid dispenser  122  may be used to deposit droplets of liquid formable material  124  (e.g., a photocurable polymerizable material) onto the substrate  102  with the volume of deposited material varying over the area of the substrate  102  based on at least in part upon its topography profile. Different fluid dispensers  122  may use different technologies to dispense formable material  124 . When the formable material  124  is jettable, ink jet type dispensers may be used to dispense the formable material. For example, thermal ink jetting, microelectromechanical systems (MEMS) based ink jetting, valve jet, and piezoelectric ink jetting are common techniques for dispensing jettable liquids. 
     The planarization system  100  may further comprise a curing system that includes a radiation source  126  that directs actinic energy, for example, UV radiation, along an exposure path  128 . The planarization head  120  and the substrate positioning state  106  may be configured to position the superstrate  108  and the substrate  102  in superimposition with the exposure path  128 . The radiation source  126  sends the actinic energy along the exposure path  128  after the superstrate  108  has contacted the formable material  128 .  FIG. 1  illustrates the exposure path  128  when the superstrate  108  is not in contact with the formable material  124 . This is done for illustrative purposes so that the relative position of the individual components can be easily identified. An individual skilled in the art would understand that exposure path  128  would not substantially change when the superstrate  108  is brought into contact with the formable material  124 . 
     The planarization system  100  may further comprise a camera  136  positioned to view the spread of formable material  124  as the superstrate  108  contacts the formable material  124  during the planarization process.  FIG. 1  illustrates an optical axis  138  of the field camera&#39;s imaging field. As illustrated in  FIG. 1 , the planarization system  100  may include one or more optical components (dichroic mirrors, beam combiners, prisms, lenses, mirrors, etc.) which combine the actinic radiation with light to be detected by the camera  136 . The camera  136  may include one or more of a CCD, a sensor array, a line camera, and a photodetector which are configured to gather light at a wavelength that shows a contrast between regions underneath the superstrate  108  and in contact with the formable material  124  and regions underneath the superstrate  108  but not in contact with the formable material  124 . The camera  136  may be configured to provide images of the spread of formable material  124  underneath the superstrate  108 , and/or the separation of the superstrate  108  from cured formable material  124 . The camera  136  may also be configured to measure interference fringes, which change as the formable material  124  spreads between the gap between the surface  112  and the substrate surface. 
     The planarization system  100  may be regulated, controlled, and/or directed by one or more processors  140  (controller) in communication with one or more components and/or subsystems such as the substrate chuck  104 , the substrate positioning stage  106 , the superstrate chuck  118 , the planarization head  120 , the fluid dispenser  122 , the radiation source  126 , and/or the camera  136 . The processor  140  may operate based on instructions in a computer readable program stored in a non-transitory computer memory  142 . The processor  140  may be or include one or more of a CPU, MPU, GPU, ASIC, FPGA, DSP, and a general-purpose computer. The processor  140  may be a purpose-built controller or may be a general-purpose computing device that is adapted to be a controller. Examples of a non-transitory computer readable memory include but are not limited to RAM, ROM, CD, DVD, Blu-Ray, hard drive, networked attached storage (NAS), an intranet connected non-transitory computer readable storage device, and an internet connected non-transitory computer readable storage device. 
     In operation, either the planarization head  120 , the substrate position stage  106 , or both vary a distance between the superstrate  118  and the substrate  102  to define a desired space (a bounded physical extent in three dimensions) that is filled with the formable material  124 . For example, the planarization head  120  may be moved toward the substrate and apply a force to the superstrate  108  such that the superstrate contacts and spreads droplets of the formable material  124  as further detailed herein. 
     Planarization Process 
     The planarization process includes steps which are shown schematically in  FIGS. 2 a -2 c   . As illustrated in  FIG. 2 a   , the formable material  124  is dispensed in the form of droplets onto the substrate  102 . As discussed previously, the substrate surface has some topography which may be known based on previous processing operations or may be measured using a profilometer, AFM, SEM, or an optical surface profiler based on optical interference effect like Zygo NewView 8200. The local volume density of the deposited formable material  124  is varied depending on the substrate topography. The superstrate  108  is then positioned in contact with the formable material  124 . 
       FIG. 2 b    illustrates a post-contact step after the superstrate  108  has been brought into full contact with the formable material  124  but before a polymerization process starts. As the superstrate  108  contacts the formable material  124 , the droplets merge to form a formable material film  144  that fills the space between the superstrate  108  and the substrate  102 . Preferably, the filling process happens in a uniform manner without any air or gas bubbles being trapped between the superstrate  108  and the substrate  102  in order to minimize non-fill defects. The polymerization process or curing of the formable material  124  may be initiated with actinic radiation (e.g., UV radiation). For example, radiation source  126  of  FIG. 1  can provide the actinic radiation causing formable material film  144  to cure, solidify, and/or cross-link, defining a cured planarized layer  146  on the substrate  102 . Alternatively, curing of the formable material film  144  can also be initiated by using heat, pressure, chemical reaction, other types of radiation, or any combination of these. Once cured, planarized layer  146  is formed, the superstrate  108  can be separated therefrom.  FIG. 2 c    illustrates the cured planarized layer  146  on the substrate  102  after separation of the superstrate  108 . The substrate and the cured layer may then be subjected to additional known steps and processes for device (article) fabrication, including, for example, patterning, curing, oxidation, layer formation, deposition, doping, planarization, etching, formable material removal, dicing, bonding, and packaging, and the like. The substrate may be processed to produce a plurality of articles (devices). 
     Spreading, Filling, and Curing Planarization Material Between Superstrate and Substrate 
     One scheme for minimizing entrapment of air or gas bubbles between the superstrate  108  and the substrate as the formable material droplets spread, merge and fill the gap between the superstrate and the substrate is to position the superstrate such that it makes initial contact with the formable material in the center of the substrate with further contact then proceeding radially in a center to perimeter fashion. This requires a deflection or bowing of the superstrate or substrate or both to create a curvature profile in the superstrate. However, given that the superstrate  108  is typically of the same or similar areal dimension as the substrate  102 , a useful whole superstrate bowing curvature profile requires both a significant vertical deflection of the superstrate, and a concomitant vertical motion by the superstrate chuck and planarization assembly. Such a significant vertical deflection and motion may be undesirable for control, accuracy, and system design considerations. Such a superstrate profile can be obtained by, for example, applying a back pressure to the interior region of the superstrate. However, in doing so, a perimeter holding region is still required to keep the superstrate retained on the superstrate chuck. If both the perimeter edges of the superstrate and the substrate are chucked flat during formable material droplet spreading and merging, there will be no available superstrate curvature profile in this flat chucked area. This may compromise the droplet spreading and merging, which may also lead to non-fill defects in the region. In addition, once spreading and filling of the formable material is complete, the resultant stack of a superstrate chuck, a chucked superstrate, the formable material, substrate, and a substrate chuck can be an over-constrained system. This may cause a non-uniform planarization profile of the resultant planarized film layer. That is, in such an over-constrained system, all flatness errors or variations from the superstrate chuck, including front-back surface flatness, can be transmitted to the superstrate and impact the uniformity of the planarized film layer. 
     To resolve the above issues, in one embodiment, a multi-zone superstrate chuck  118  is provided as shown in  FIGS. 3 a  and 3 b   . The superstrate chuck  118  includes a center zone  301  and a series of ring zones  303  about the center zone  301 . The ring zones  303  may be defined into a peripheral ring zone  303   b  around an edge, a perimeter, or a periphery of the superstrate chuck  118  and a plurality of inner ring zones  303   a  located between the center zone  301  and the peripheral ring zone  303   b . The multiple ring zones  303  may be defined by a series of lands  307  protruding from a surface of the superstrate chuck  118 . As shown in  FIGS. 3 a  and 3 b   , the lands  307  may be formed about the center zone  301 . In each of the ring zones  303 , at least one port  305  is formed to connect through the superstrate chuck  118 , to allow a pressure source to apply positive pressure or negative pressure, for example, vacuum, to a superstrate retained thereby. 
       FIG. 3 b    shows a side cross-sectional view of the superstrate chuck  118 . Each of the lands  307  protrudes from a surface of the superstrate chuck  118  with a height. The lands  307  include a peripheral land  307   b  surrounding the peripheral ring zone  303   b  and a series of inner lands  307   a  between the center zone  301  and the peripheral ring zone  303   b . As shown in  FIG. 3 b   , the inner lands  307   a  have substantially the same height, while the height of the peripheral land  307   b  is less than those of the inner lands  307   a . The center zone  301  of the superstrate chuck  118  may be in the form of a circular cavity, such that the pressure source (not shown) may apply air or gas pressure through the associated channel  308  and port  305  to deflect a center portion of a retained superstrate. Vacuum pressure may likewise be applied to center zone  301  through the same channel and port. The center zone  301  of the superstrate chuck  118  may be aligned with a center portion of the retained superstrate. Similarly, the peripheral ring zone  303   a  may be aligned with a perimeter or a periphery of the retained superstrate. Surrounding ring zones  303  are likewise provided with respective channels  308  and ports  305  for application of pressure or vacuum. 
     Turning to  FIGS. 4 a -4 e   , a process for contacting, spreading and merging droplets of deposited formable material  124  is depicted. As shown in  FIG. 4 a   , before the superstrate  108  is brought in contact with the formable material  124 , a positive pressure (indicated by arrow P) is applied through ports  305  to the center zone  301  of the superstrate chuck  118  to the retained superstrate  108  to deflect the center portion of the superstrate  108  towards the formable material  124 . The pressure P is applied to the center zone  301  to control an initial deflection at a predetermined range and to maintain a predetermined curvature of the superstrate  108  as shown in  FIG. 4 a   . In the meantime, a negative pressure, preferably, a vacuum (indicated by arrows V), is applied to the superstrate  108  through the ports  305  in the ring zones  303  to retain the superstrate  108  with the superstrate chuck  118 . The superstrate  108  is then brought into initial contact with the droplets of formable material  124  as show in  FIG. 4   b.    
     The deflection of the superstrate  108  is then extended from the center portion in a radially outward direction by sequentially releasing the vacuum (V) from the inner ring zones  303   a  proximal to the center zone  301 . In this fashion, the droplets of formable material are contacted, spread and merged to form a film layer with a fluid front that progresses radially outward as the superstrate contacts and conforms to the substrate. When the vacuum is sequentially released from the inner ring zones  303   a , the pressure P applied through the center zone  301  is maintained at a desired value. Pressure P may also be applied to the superstrate  108  through the channels  308  and ports  305  in the inner ring zones  303   a  from which the vacuum has been released. In the embodiment as shown in  FIGS. 4 c   , vacuum has been sequentially released from three inner rings  303   a  closest to the inner zone  301 , with pressure P sequentially applied as the vacuum has been sequentially released. Planarization head may also be moved downward during this sequential vacuum release and pressurization. 
     The deflection of the superstrate  108  is then further extended in a radial direction sequentially until the vacuum is released from all the inner ring zones  303   a , while the vacuum V applied via the peripheral ring zone  303   b  is maintained. For each of the inner ring zones  303   a , pressure P is also applied once the vacuum has been released. As shown in  FIG. 4 d   , when the vacuum has been released from all inner ring zones  303   a , the superstrate  108  is deflected to conform to the substrate  102  except for the periphery of substrate  108  which remains retained by the superstrate chuck  118  via the vacuum V applied through the peripheral zone  303   b . As such, the edge of superstrate  108  remains in a deflected, curved condition for the final spreading and merging of formable material droplets dispensed on the periphery of the substrate  102 . In addition, the peripheral land  307   b , which is lower relative to the inner lands  307   a , facilitates the maintenance of such curvature. 
     In  FIG. 4 e   , the vacuum V applied through the peripheral ring zone  303   b  is then released to in order to release the superstrate  108  entirely from the superstrate chuck  118 . This provides multiple advantages. First, by releasing the periphery of superstrate  108  from the peripheral ring zone  303   b  which had been retained in a curved condition, the spreading and merging of the remaining formable material droplets can be completed in the same center-to-perimeter radial fashion, thus continuing to minimize air or gas trapping and resultant non-fill defects. Specifically, the peripheral land  307   b  which is recessed relative to the inner lands  307   a  allows the superstrate  108  to maintain the desired curvature prior to release. Secondly, by completely releasing the superstrate  108  from the superstrate chuck  118 , any over-constraint of the superstrate  108  due to the chucking condition is removed, thereby reducing local non-uniform planarization that might otherwise occur due to such constrained conditions. Thirdly, the release of the superstrate  108  from the superstrate chuck  118  eliminates the transfer of any chuck non-flatness error or variation to the superstrate  108 , which also reduces localized non-uniform planarization variations. 
     Once the superstrate  108  is released, curing energy may be applied to cure the formable material to form the planarized layer. As previously mentioned, the curing source may a light beam for curing the formable material  124 . In one embodiment, the size of the light beam may be adjusted or controlled with reference to a diameter of the superstrate. The light beam can also be controlled to be incident on the substrate with a predetermined angle. During curing, a lateral position (i.e., in X-Y plane) of the substrate  102  relative to a curing source may be adjusted. After the curing process, the superstrate  108  is re-retained by the superstrate chuck  118  and superstrate  108  is then separated from the substrate as further described herein. 
       FIG. 5  illustrates a flow chart of the planarization process described as shown in  FIGS. 3 and 4 . In Step  501 , formable material droplets  124  are dispensed on the substrate  102 . The center zone of the superstrate  108  is deflected towards the formable material droplets  124  in step S 502 . The deflected superstrate  108  is then advanced by the superstrate chuck  118  to be in contact with the formable material  124  in step S 503 . The deflection of the superstrate  108  is extended from the center zone towards the perimeter of the superstrate  108  in step S 504 . Application of force to hold the superstrate  108  by the superstrate chuck  118 , for example, by vacuum applied to the perimeter of the superstrate  108  is then stopped, such that the superstrate  108  is released (i.e., de-chucked) from the superstrate chuck  118  in step S 506 . The formable material  124  is cured in step S 507 . After curing, the superstrate  108  is re-retained by the superstrate chuck  118  to separate the superstrate  108  from the cured formable material  146 . 
     When using, for example, a UV photocurable material as the formable material  124 , it is desirable that the superstrate chuck  118  is transparent with high UV light transmissivity UV curing (as well as high light transmissivity for imaging, for example, by the camera  136  as shown in  FIG. 1 ). As discussed above, pneumatic supply channels  308  and ports  305 , zones  303 , and lands  307  are integrated into the superstrate as shown in  FIGS. 3 and 4 . These structures may create a problem for UV curing. Particularly, the UV transmissivity in areas below the channels  308 , and lands  307  can be significantly reduced compared to areas with no such features, leading to an under-curing or non-uniform curing of the formable material. This phenomenon is sometimes referred to as a “shadowing effect”. Shadowing effects may be particularly significant at edges of the lands  307 . Additionally, when the superstrate  100  is chucked to the lands  307 , there will be thin air gaps as two surfaces do not optically touch each other. This type of thin gap can sometimes block UV completely. This phenomenon is known as the “thin film effect” between the land and the superstrate. 
     One solution to the above “shadow effect” includes movement of the stack of superstrate and substrate on a wafer stage in x, y and/or θ coordinates after de-chucking (i.e., releasing) the superstrate from the superstrate chuck. By moving the wafer stage in this fashion during UV exposure, regions of the superstrate and substrate that would have remained under the channels, ports, and lands can be periodically moved to regions below the superstrate chuck where no chuck features are present. The relative motion required can be estimated from the following equation (1): 
                       I   m     =           I   h     ⁡     (       w   h     -     w   l       )       +       I   l     ⁢     w   l           w   h         ,           (   1   )               
where I m  is the desired average intensity across range of motion, I h  is the high intensity across no feature area of the chuck (i.e., the maximum or “max” intensity), I l  is the intensity at the subject feature (i.e., the lowest or “low” intensity), w h  is the estimated motion range to achieve I m , w l  is the subject feature width (e.g., width of the land, port, or channel). For example, assuming 100% UV transmission in the featureless areas, and assuming the desired I m  is 90% of that value, and further assuming w i =1 mm, from Equation (1), the desired range of relative motion w h =8.0 mm. Alternatively, the UV source can be moved by tipping or tilting the source relative to the superstrate chuck to change the angle of the UV light incident on the superstrate chuck, which can also reduce the shadowing effect near the subject features. The “thin film effect” can be avoided by relative movement in the z-axis direction to create a sufficient gap between the superstrate and superstrate chuck, for example, by de-chucking the superstrate and moving the wafer stage in the z-direction away from the superstrate chuck or. The various solutions described above can be applied individually or in combination to improve the total UV dosage uniformity in certain regions and minimize shadowing and thin film effects. In various embodiments, the applied UV light beam can be smaller, same size, or larger than the substrate or superstrate. In one embodiment, the applied UV light beam can be larger than the substrate by a dimension that accommodates the above relative motion w h  while continuing to expose the entirety of the substrate to the UV light.
 
Separating Superstrate from Cured Planarized Film Layer
 
     Once the formable material is cured and the planarized film layer is formed, it is necessary to remove or release the superstrate from the formed layer. However, when the superstrate and substrate have the same or similar areal dimensions, it is difficult to initiate and propagate a separation crack between the superstrate and formed layer as is necessary in order to fully separate the superstrate from the formed layer. This problem can be resolved by the structure and methods shown in  FIGS. 6-8 . As shown in  FIGS. 6 a  and 6 b   , substrate chuck  604  includes retractable pin  606  located at the periphery of the chuck that can be aligned with notch  608  on substrate  102 . Such a notch (e.g. wafer notch) is common to semiconductor wafers for purposes of orienting the wafer during processing and handling. In operation, retractable pin  606  is positioned in alignment with notch  608  located on substrate  102 . To initiate separation, pin  606  moves upwardly through notch  608  and into contact with a point  610  at the edge of superstrate  108 , as shown in FIG.  6   a . The force applied by pin  606  is sufficient to initiate separation crack  601  between superstrate  108  and cured layer  146  on substrate  102 . Once the crack  601  is created, the edge of superstrate  108  is deflected towards the superstrate chuck  118  by application of vacuum pressure through port  305  of superstrate chuck  118 . This is facilitated by land  307   b  of the superstrate chuck  118  being shorter than the adjacent land  307   a , which provides a space for the edge of superstrate  108  to be deflected away from the substrate  102  and towards the superstrate chuck  118 . The force applied to create the crack  601  can depend upon the geometric and physical conditions of the superstrate, planarized film layer, and substrate. Alternatively, the crack  601  may be created by introducing a positive pressure between the substrate  102  and the superstrate  108 , as shown in  FIG. 6 c   . Here substrate chuck  614  includes nozzle  616  connected to a positive fluid pressure source (not shown). Upon activation of nozzle  616 , positive fluid pressure Pi is delivered through nozzle  616  to point  610  at the edge of superstrate  118  with sufficient force to initiate separation crack  601 . The positive fluid pressure may include a flow of clean dry air, helium, or nitrogen. While creating the crack  601 , the superstrate  102  is retained in the superstrate chuck  118 , and the substrate  102  is retained by the substrate chuck  104 . 
       FIGS. 7-8  illustrate the progression of separation.  FIG. 7 a    shows a top down view of the superstrate  118  in full contact (as indicated by the shaded region) with the formed layer on substrate. In  FIG. 7 b   , separation crack  601  has been initiated as described above. Once the crack  601  is initiated, a high flow of negative pressure or vacuum is applied to outer ring zone  303   b  of superstrate chuck  118  so as to engage the edge of the superstrate  108  and propagate the separation crack  601  about the outer zone ring  303   b . This propagation proceeds circumferentially in both directions from notch  608 , as indicated by arrows C. To assist the propagation of crack  601  about the outer ring zone  303   b , additional lateral air flow (not shown) can be supplied between the substrate  102  and the superstrate  108  as the crack propagation progresses.  FIG. 7 c    shows the crack  601  fully propagated about outer ring zone  303   b.    
     Once the separation crack has fully propagated around the outer ring zone, an upward motion may be applied along the Z-axis direction of the superstrate  108  to complete separation of the superstrate  108  from the cured layer on the substrate.  FIG. 8  shows superstrate  108  fully separated from substrate  102 . In completing separation, a significant upward motion of the superstrate  108  relative to the substrate  102  may induce a shearing stress at the remaining in-contact area between the superstrate  108  and the substrate  102 . Alternatively, Z-direction motion can be stopped at an earlier desired position and separation can be advanced and concluded through continued vacuum pressure application to the inner and/or center ring zones. Such shear stress can be minimized by applying vacuum to one or more of the inner ring zones  303   a  and/or the center zone  301  during the continued separation. 
       FIG. 9  illustrates a flow chart of the separation process as described and shown in  FIGS. 7 and 8 . In Step S 901 , a separation crack initiated between the superstrate  108  and the cured layer. The separation crack is then propagated about a periphery of superstrate  108  in step S 902 . In step S 903 , the remainder of the superstrate is separated from the cured layer. In the embodiments discussed above, the separation of the superstrate  108  and the substrate  102  includes a step of creating a crack by a mechanical force such as pushing pin or air pressure, a step of applying vacuum pressure to the outer zone to propagate the crack, securely holding the superstrate  108 , moving the superstrate  108  upwardly in Z-direction and away from the substrate  102  with a force safe enough to avoid de-chucking the superstrate upwardly, and a step of applying vacuum to the center of the superstrate  108  during the upward Z-direction movement to complete the separation. Alternatively or in combination with the above Z-direction motion schemes, the propagation of the separation can also be affected by continuously applying in-plane (or lateral) directional flow with high pressure from one or more sides of the substrate (not shown). 
     In the  FIG. 6  embodiments, crack initiation is initiated by an upward force applied through wafer notch  608  by either a mechanical pin  606  ( FIG. 6 a   ) or fluid nozzle  616  ( FIG. 6 b   ).  FIG. 10  shows a further embodiment of a substrate chuck configured to initiate a separation crack. Here, substrate chuck  624  includes a separate retractable pin  626  that can initiate a separation crack when the superstrate  108  and substrate are arranged non-concentrically. This non-concentric arrangement results in a portion  628  of the superstrate  108  that overhangs the substrate  102 . The crack  602  can be created by applying the force to the overhanging portion  110  via movement of pin  626 . Alternatively, the overhanging portion  608  may also be obtained by using a superstrate slightly bigger than the substrate. In this way, the superstrate  108  can still be arranged concentric with the substrate  102 . In either case, substrate chuck  624  can further include mechanical pins or nozzles, such as in the embodiments of  FIG. 6 a    or  6   b  or otherwise, that are spaced apart from pin  626  to create multiple points about the superstrate periphery for initiating the separation crack. 
     Superstrate Chuck 
     As discussed above, the superstrate  108  is preferably retained or supported by the superstrate chuck  118  that applies pressure or vacuum (negative pressure) to a volume between the superstrate and the chucking surface within ring zones  303  that are defined by lands  307  extending from the chucking surface. Apart from the outermost land  307   a , the inner lands  307   b  preferably have the same height such that the depths of the gaps between the adjacent inner lands  307   b  remains constant. The land heights (i.e., depth of the gaps) is usually kept very small, for example, in the order of about tens to thousands of microns, for reasons such as minimizing gas filling or evacuation response time, land stiffness characteristics, limiting thermal effects, such as expansion or contraction, etc. In operation, when vacuum is applied to a ring zone to retain the superstrate against the lands of the zone, a vacuum seal is created at the superstrate-land interface. However, when a sufficient force or a pressure is applied to the superstrate in the opposition direction of the chucking vacuum, the substrate may be lifted off the land of the chuck. At a certain gap between the superstrate and land, the vacuum seal fails or otherwise leaks resulting in a reduced or even zero vacuum pressure within the zone. The superstrate may then become unintentionally de-chucked from the chuck. Further, even if superstrate is does not become de-chucked, vacuum leakage can disrupt the level of control required, for example, when sequentially releasing vacuum pressure in adjacent ring zones in the  FIGS. 4 and 5  process. Such leakage at the outer land can also negatively impact the controlled retention of the desired outer edge curvature of the superstrate in the process of  FIGS. 4 to 5 . Similarly, outer land leakage can disrupt the separation crack initiation and propagation in the process of  FIGS. 7 to 9 . 
     To counter such undesirable leakage, superstrate chuck  1118  is provided that incorporates trench structures  1109 , as shown in  FIGS. 11 a  and 11 b   . Similar to superstrate chuck  118 , the superstrate chuck  1118  likewise includes a plurality of lands  307 , which can be defined into a series of inner lands  307   a  and a peripheral land  307   b  protruding from a surface  1119  of the superstrate chuck  1118 . As shown in  FIGS. 11 b    and 12, the surface  1119  is the holding or retaining surface for holding or retaining the superstrate  108 . A series of inner zones  303   a  are defined by the lands  307   a . In at least one of the ring zones  303 , a trench  1109  is formed that is recessed from the surface of the chuck  1118 . The trench can be concentric and positioned between the corresponding lands of the ring zone. Trenches  1109   a  formed in the inner ring zones  303   a  are positioned at locations distal to the center of the chuck  1118  with respect to the associated inner ring zone width. In contrast, the trench  1109   b  formed in the peripheral ring zone  303   b  is positioned at an area proximal to the center of the substrate chuck  1118  relative to the outer zone ring width. That is, the trenches  1109   a  formed in the inner ring zones  303   a  are formed at an outer diameter of the corresponding inner ring zones  303   a , while the trench  1109   b  formed in the peripheral ring zone  303   b  is formed at an inner diameter of the peripheral zone  303   b.    
     In operation, trenches  1109  act as a buffer that provides a uniform source of high vacuum pressure that continues to act on the superstrate even in the presence of a gap between superstrate at the land distal to the trench. In this fashion, the sequential outwardly radial release of vacuum and application of positive pressure to the center zone and adjacent ring zones can proceed in a controlled manner. That is, the applied vacuum pressure in a given ring zone can be maintained, even as positive pressure is applied to the adjacent inner zone in an amount that may deflect the superstrate enough to produce a gap at the distal land. In other words, the provision of trenches  1109  allow for some leakage to be tolerated, without disruption to the intended process. Similarly, the trench  1109   b  located in the peripheral ring zone with smaller outer land height operates to maintain adequate vacuum pressure in the outer ring zone even in the presence of a small gap at the outer land. This enables the outer periphery of the superstrate to be held at the desired curvature both for final spreading and merging of deposited formable material droplets (see  FIG. 4 d   ) and for separation crack initiation and propagation (see e.g.  FIG. 6 ), even in the presence of some leakage. 
       FIG. 12  is an enlarged cross-sectional view of exemplary trench structure  1109   b . The particular trench dimensions and relevant location within the ring zone needed to achieve the desired vacuum buffering performance is dependent upon the superstrate chuck land heights and ring zone width. In the example shown in  FIG. 12 , the trench  1109   b  is located within ring zone  303   b  and recessed from the chuck surface. In this example, the outer land  307   b  has a height h 1  less than a height h 2  of the inner land  307   a . In typical usage, the differences in land heights may range from about 5 microns to about 50 microns. Ring zone  303   b  has a width d. Trench  1109   b  is positioned with a first edge at a distance d 1  from land  307   b  and a second edge at a distance d 2  from land  307   a . Trench  1109   b  has a depth h 3  and a width d 3 . In this embodiment, the relationship between these parameters satisfies the following conditions:
 
 h   1   &lt;h   2  
 
 h   3 &gt;10 h   2  
 
 d   3 &lt;0.5 d  
 
 d   1   &gt;d   2   +d   3 .
 
The port  305  connecting the trench  1109   b  to the pressure supply (not shown) intersects with or is otherwise located within the trench. If the port does not intersect with the trench, the requisite high pressure cannot be maintained, and the trench will be ineffective. In the above embodiment, the outer land h 1  is where the leakage is expected to occur. For inner ring trenches  1109   b , the land heights may be the same, i.e., h 1 =h 2 . In this case, the distance d 1  is measured from the designated land (i.e., h 1  or h 2 ) where the leakage is expected. For example, in the embodiment of  FIGS. 11 a  and 11 b   , the inner rings zone  303   a  include trenches  1109   a  positioned closer to the outer lands (as measured radially from the chuck center) of their respective ring zones to mitigate against leakage at the inner lands during the sequential vacuum release and subsequent pressurization of the ring zones as described in the processes associated with  FIGS. 4-5 .
 
     Further modifications and alternative embodiments of various aspects will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only. It is to be understood that the forms shown and described herein are to be taken as examples of embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description.