Patent Publication Number: US-2021181625-A1

Title: Methods and apparatus for creating a large area imprint without a seam

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/924,763, filed Mar. 19, 2018, which herein is incorporated by reference. 
    
    
     BACKGROUND 
     Field 
     Embodiments of the present disclosure generally relate to imprint lithography, and more particularly to methods and apparatus for creating a large area imprint without a seam. 
     Description of the Related Art 
     Imprint lithography is a contact patterning method that can be used to fabricate nanometer scale patterns. Generally, imprint lithography begins by creating a template of a pattern. A liquid, such as a photoresist, is deposited on the substrate to be patterned. Then, the patterned template is pressed against the liquid to imprint the pattern on the substrate. The patterned substrate is then cured to solidify the patterning in the photoresist on the substrate. 
     However, conventional imprint lithography methods and apparatus have various challenges. For example, conventional imprint lithography methods are not suitable for large area substrates (greater than 300 mm), such as display devices, because conventionally used masters are not large enough to pattern large area displays. As such, some conventional imprint methods have used multiple masters, which have been adhered to one another. However, a seam is formed between the masters and at the periphery, which is then transferred into the patterning on the substrate. The patterned irregularities at the seams and periphery can cause decreased device efficiency and even device failure. For example, in the case of a light guided panel (LGP), when a seam is imprinted into the LGP, it becomes a surface feature that could direct or out-couple light out of the LGP. In the case of liquid crystal display (LCD), when a seam is imprinted into the LCD, the viewer will see the seam in the display. 
     Therefore, there is a need for improved imprint lithography methods and apparatus that can be used to imprint large area substrates. 
     SUMMARY 
     Embodiments of the present disclosure generally relate to imprint lithography, and more particularly to methods and apparatus for creating a large area imprint without a seam. Methods disclosed herein generally include separating the curing time of the features in a stamp or product from the curing time of the seam and the periphery. The seam and periphery can be cured first or the seam and periphery can be cured last. Additionally, the seam curing operations can be performed on the master, on the stamp, or on the final product. 
     In one embodiment, an imprint lithography method is disclosed. The method includes imprinting a stamp material with a plurality of masters adhered to a backing plate to form a stamp, each master having a plurality of features thereon, and each pair of the plurality of masters having a seam therebetween, positioning a mask between an ultraviolet light source and the stamp material, and exposing the stamp material to ultraviolet light from the ultraviolet light source to form cured portions and uncured portions of the stamp material. 
     In another embodiment, an imprint lithography method is disclosed. The method includes imprinting a stamp material with a plurality of masters adhered to a backing plate to form a stamp, each master having a plurality of features thereon, and each pair of the plurality of masters having a seam therebetween, imprinting a photoresist material on a substrate with the stamp, positioning a mask between an ultraviolet light source and the photoresist material, and exposing the photoresist material to ultraviolet light from the ultraviolet light source to form cured portions and uncured portions of the photoresist material. 
     In yet another embodiment, an imprint lithography method is disclosed. The method includes adhering a plurality of masters to a backing plate, each master having a plurality of features thereon, and each pair of the plurality of masters having a seam therebetween, filling the seam between each pair of the plurality of masters with a filler material, forming a stamp by imprinting a stamp material with the plurality of masters, imprinting a photoresist material over a substrate with the stamp, and removing the stamp from the imprinted photoresist material to form a final product having a positive image of the plurality of features and the filled seam thereon. 
     In yet another embodiment, an imprint lithography apparatus is disclosed. The apparatus includes a UV transparent backing plate and at least two masters coupled to the UV transparent backing plate, each of the at least two masters having a plurality of features thereon, and the at least two masters having a seam therebetween. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments. 
         FIGS. 1A-1F  depict various stages of a substrate patterning method according to embodiments disclosed herein. 
         FIGS. 2A-2D  depict various stages of a substrate patterning method according to embodiments disclosed herein. 
         FIGS. 3A-3D  depict various stages of a substrate patterning method according to embodiments disclosed herein. 
         FIGS. 4A-4B  depict various stages of a substrate patterning method according to embodiments disclosed herein. 
         FIGS. 5A-5F  depict various stages of a substrate patterning method according to embodiments disclosed herein. 
         FIGS. 6A-6F  depict various stages of a substrate patterning method according to embodiments disclosed herein. 
     
    
    
     To facilitate understanding, identical reference numerals have been used, wherever possible, to designate identical elements that are common to the Figures. Additionally, elements of one embodiment may be advantageously adapted for utilization in other embodiments described herein. 
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure generally relate to imprint lithography, and more particularly to methods and apparatus for creating a large area imprint without a seam. Methods disclosed herein generally include separating the curing time of the features in a stamp or product from the curing time of the seam and the periphery. The seam and periphery can be cured first or the seam and periphery can be cured last. Additionally, the seam curing operations can be performed on the master, on the stamp, or on the final product. 
     The embodiments that follow will refer to methods and apparatus for creating a large area imprint without a seam. The embodiments are also useful to cure similar seam-like challenges at the periphery of the master, stamp or final product. 
       FIGS. 1A-1F  depict various stages of a substrate patterning method according to embodiments disclosed herein. The method depicted in  FIGS. 1A-1F  provides a master-level solution to seam and periphery challenges. The method begins by adhering a plurality of masters  104  onto a backing plate  102 . Two masters  104  are adhered to the backing plate  102  in the embodiment shown in  FIG. 1A . The masters  104  have a pattern of features  105  thereon. A seam  106  is formed between the two masters  104 . The seam  106  is filled with a filler material  108 , as shown in  FIG. 1B . Generally, the filler material  108  will not fill the seam  106  in a manner that results in a completely flat surface. Instead, if the seam  106  is underfilled with filler material  108 , the seam  106  will become concave, as shown in  FIG. 1B . In another embodiment, the seam  106  is overfilled with filler material  108  and becomes convex. 
     As shown in  FIG. 1C , a stamp material  110  is contacted by the masters  104  to form a stamp  112 . As shown in  FIG. 1D , the stamp  112  is a negative pattern of the masters  104 . As such, the stamp  112  includes a convex portion  114  at the position corresponding to the concave seam  106  and negative features  116 . The stamp  112  is then used to pattern a photoresist material  118  which is deposited over a substrate  120 , as shown in  FIG. 1E , to form a final product  122 , as shown in  FIG. 1F . The final product  122  includes a photoresist material  118  which has been patterned with a plurality of features  125 , as well as concave portion  127 . Since the method includes two transfer imprints, at the stamp level and the final product level, the final product  122  is a positive image of the masters  104  and the seam  106 . 
     The filler material  108  is generally any suitable material. In one example, the filler material  108  is a polymer. In another example, the filler material  108  is a low viscosity adhesive that is able to fill gaps or seams that are between about 100 μm and about 500 μm in width, such as a low viscosity silicone. In some examples, the filler material  108  is able to fill gaps or seams through capillary action. The stamp material  110  is generally any suitable material. In one example, the stamp material  110  is a polydimethyl siloxane material (PDMS), or any other variation to PDMS that has been spin coated or deposited on a substrate. In further examples, the stamp material  110  is any soft material that functions as an intermediate pattern transfer medium, such as polyvinyl alcohol (PVA) based. The substrate is generally any suitable substrate material, including but not limited to, glass, fused silica, quartz, poly(methyl methacrylate) (PMMA), polyethylene terephthalate (PET) and polycarbonate. 
     In further embodiments, the method includes fewer or additional operations to pattern the substrate. For example, in one embodiment, an additional transfer imprint operation is performed in order to make a negative image of the masters on the substrate. In another embodiment, the masters are used to pattern the substrate directly, and the intermediate transfer imprint operations are eliminated. 
       FIGS. 2A-2D  depict various stages of a substrate patterning method according to embodiments disclosed herein. The method depicted in  FIGS. 2A-2D  provides a stamp-level solution to seam and periphery challenges in which the seam and periphery are cured last. The method begins by adhering a plurality of masters  204  onto a backing plate  202 . Two masters  204  are adhered to the backing plate  202  in the embodiment shown in  FIG. 2A . The masters  204  have a pattern of features  205  thereon. A seam  206  is formed between the two masters  204 . As shown in  FIG. 2A , the seam  206  is left unfilled. In other embodiments, the seam  206  is underfilled such that the seam  206  is concave. 
     Next, shown in  FIG. 2B , the masters  204  imprint a stamp material  210 . After the masters  204  imprint the stamp material  210 , a mask  224  is positioned between the stamp material  210  and an ultraviolet (UV) light source  226 , as shown in  FIG. 2C . In operation, the mask  224  prevents UV light from reaching the portion of the stamp material  210  corresponding to the seam  206 . Since the UV light from the UV light source  226  does not reach the portion of the stamp material  210  corresponding to the seam  206 , the seam  206  will be imprinted but not cured in the stamp material  210 . 
     After the unmasked portions of the stamp material  210  have been cured, shown as cured portions  228  in  FIG. 2D , the masters  204  are removed from the stamp material  210  and the uncured portions  230  (corresponding to the seam  206  and periphery) of the stamp material  210  flow or “relax” until the uncured portions  230  are flat along the surface of the substrate  221 , as shown in  FIG. 2D . After the uncured portions  230  have flowed and are flat along the surface of the substrate  221 , the stamp material  210  is cured again with additional UV light to create a stamp  212  having features  225  thereon. The stamp  212  can be used to imprint a final product, such as a large area substrate, without leaving a seam in the final product. 
     The stamp material  210  is generally any suitable material. In one example, the stamp material  210  is a PDMS material. In another example, the soft stamp material  210  is made from PVA. The substrate  221  is generally any suitable substrate material, including but not limited to, glass, PMMA, and polycarbonate. 
     In another embodiment, the seam  206  is overfilled with a filler material, such as a polymer. As shown in  FIGS. 2A-2D  the stamp material  210  is deposited on a substrate  221 ; in further embodiments, however, the stamp material  210  is directly coated on the masters  204  and is later removed. In further embodiments, the uncured portions  230  are washed away instead of subsequently cured. For example, the uncured portions  230  may be removed using one or more solvents selected to remove the particular stamp material  210 . Additionally, further embodiments contemplate using a maskless direct write laser system to cure predetermined portions of the material using a focused, narrow beam of radiation. For example, the maskless direct write system can be used to cure the regions with features during the imprint method. The maskless direct write laser system then also can be used to cure the seam and periphery regions after the masters have been removed. 
     In further embodiments, the method includes fewer or additional operations to pattern the substrate. For example, in one embodiment, an additional transfer imprint operation is performed in order to make a negative image of the masters on the substrate. In another embodiment, the masters are used to pattern the substrate directly and the intermediate transfer imprint operations are eliminated. 
       FIGS. 3A-3D  depict various stages of a substrate patterning method according to embodiments disclosed herein. The method depicted in  FIGS. 3A-3D  provides a stamp-level solution to seam and periphery challenges in which the seam and periphery are cured first. The method begins by adhering a plurality of masters  304  onto a backing plate  302 . Two masters  304  are adhered to the backing plate  302  in the embodiment shown in  FIG. 3A . The masters  304  have a pattern of features  305  thereon. A seam  306  is formed between the two masters  304 . As shown in  FIG. 3A , the seam  306  is left unfilled. In other embodiments, the seam  306  is underfilled such that the seam  306  is concave. 
     Next, a stamp material  310  deposited over a substrate  321  is cured. More particularly, a mask  324  is positioned between the stamp material  310  and a UV light source  326 , as shown in  FIGS. 3B-3C . In operation, the mask  324  prevents UV light from reaching the portions, shown as uncured portions  330 , of the stamp material  310  that will be imprinted with the features  305 . The unmasked portions of the stamp material  310  are cured, shown as cured portions  328 . The cured portions  328  correspond to the areas of the seam  306  and periphery. The masters  304  then imprint the uncured portions  330  of the stamp material  310  while the cured portions  328  are not imprinted, as shown in  FIG. 3C . After being imprinted, the imprinted uncured portions  330  are cured. The masters  304  and backing plate  302  are then removed to form a stamp  312  having features  325  thereon, as shown in  FIG. 3D . The stamp  312  can be used to imprint a final product, such as a large area substrate, without leaving a seam in the final product. 
     The stamp material  310  is generally any suitable material. In one example, the stamp material  310  is a PDMS material. The substrate  321  is generally any suitable substrate material, including but not limited to, glass, PMMA, and polycarbonate. 
     In another embodiment, the seam  306  is overfilled with a filler material, such as a polymer. Further embodiments contemplate using a maskless direct write laser system to cure the regions with features before the imprint operations. For example, the maskless direct write laser system is used to cure the seam  306  and periphery regions before the masters  304  have imprinted the stamp material  310 . Additionally, the maskless direct write laser system can be used to cure the rest of the stamp material  310  after the stamp material  310  has been imprinted by the masters  304 . 
     As shown in  FIGS. 3B-3C , the UV light source  326  is positioned below the stamp material  310 . However, in the embodiment shown in  FIG. 4A , a UV light source  426  is positioned above the backing plate  402 , the masters  404  and the stamp material  410 . In this embodiment, the masters  404  operate as a self-aligned mask such that the UV light does not reach the portions of the stamp material  410  that are below the masters  404 , as shown by uncured portions  430 . Accordingly, the backing plate  402  comprises any suitable material that is transparent to the wavelength of the UV light being used for curing. Suitable backing plate materials include, but are not limited to, glass, quartz, sapphire and fused silica. As shown in  FIG. 4B , depending on the angle of the UV light, a region of the stamp material  410  that is cured is generally slightly larger than the seam  406  to improve the mechanical stability of the imprinted stamp. Stated differently, there is generally an overlapping region  431  at the edges of the masters  404  such that the region of the stamp material  410  thereunder is cured. Other methods and configurations are also contemplated to obtain a slight overlap between cured region of the stamp material  410  and the masters  404 . The size of the overlapping region  431  is generally selected based on the flexure of the cured regions and the masters  404  to minimize the impact on the pattern of features  405 , while also achieving seamless or nearly seamless transfer. 
     The overlapping region  431  is useful to remove or reduce a small step-height at the end of the seam  406  that may result when the masters  404  transfer the pattern of features  405  into the stamp material  410 . After the operation shown in  FIG. 4B , subsequent imprint steps are used to transfer the pattern on the masters  404  to the stamp material  410 , which is then cured. 
       FIGS. 5A-5F  depict various stages of a substrate patterning method according to embodiments disclosed herein. The method depicted in  FIGS. 5A-5F  provides a product-level solution to seam and periphery challenges in which the seam and periphery are cured last. The method begins by adhering a plurality of masters  504  onto a backing plate  502 . Two masters  504  are adhered to the backing plate  502  in the embodiment shown in  FIG. 5A . The masters  504  have a pattern of features  505  thereon. A seam  506  is formed between the two masters  504 . The seam  506  is filled with a filler material  508 , as shown in  FIG. 5B . Generally, the filler material  508  will not fill the seam  506  in a manner that produces a completely flat surface. Instead, if the seam  506  is overfilled with filler material  508 , the filled seam  506  will become convex, as shown in  FIG. 5B . In another embodiment, the filled seam  506  is underfilled with filler material  508  and becomes concave. 
     As shown in  FIG. 5C , a stamp material  510  is contacted by the masters  504  to form a stamp  512 . As shown in  FIG. 5D , the stamp  512  is a negative pattern of the masters  504 . As such, the stamp  512  includes a concave portion  514  at the position corresponding to the convex seam  506  and negative features  516 . The stamp  512  is then used to pattern a photoresist material  518  which is deposited over a substrate  520 . As shown in  FIG. 5E , a mask  524  is positioned between the stamp  512  and a UV light source  526 . In operation, the mask  524  prevents UV light from reaching the seam  506  and periphery of the stamp  512 , as shown by uncured portion  530 , such that the seam and periphery are imprinted, but not cured. The stamp  512  is then removed and a final product  522  is formed, as shown in  FIG. 5F . The final product  522  includes uncured portion  530  that flows or “relaxes” until the uncured portion  530  is flat along the surface of the substrate  521 . After the uncured portion  530  has flowed and is flat on the surface of the substrate  521 , the final product  522  is cured again with additional UV light to create a final product  522  having features  525  thereon that is without a seam. 
     As shown in  FIGS. 5A-5F  the photoresist material  518  is deposited on a substrate  520 ; in further embodiments, however, the photoresist material  518  is directly coated on the stamp  512  and is later removed. In further embodiments, the uncured portion  530  may be washed away instead of subsequently cured. Additionally, further embodiments contemplate using a maskless direct write laser system to cure the regions with features during the imprint method. 
       FIGS. 6A-6F  depict various stages of a substrate patterning method according to embodiments disclosed herein. The method depicted in  FIGS. 6A-6F  provides a product-level solution to seam and periphery challenges in which the seam and periphery are cured first. The method begins by adhering a plurality of masters  604  onto a backing plate  602 . Two masters  604  are adhered to the backing plate  602  in the embodiment shown in  FIG. 6A . The masters  604  have a pattern of features  605  thereon. A seam  606  is formed between the two masters  604 . The seam  606  is filled with a filler material  608 , as shown in  FIG. 6B . Generally, the filler material  608  will not fill the seam  606  in a manner that provides a completely flat surface. Instead, if the seam  606  is overfilled with filler material  608 , the filled seam  606  will become convex, as shown in  FIG. 6B . In another embodiment, the filled seam  606  is underfilled with filler material  608  and becomes concave. 
     As shown in  FIG. 6C , a stamp material  610  is contacted by the masters  604  to form a stamp  612 . As shown in  FIG. 6D , the stamp  612  is a negative pattern of the masters  604 . As such, the stamp  612  includes a concave portion  614  at the position corresponding to the convex seam  606  and negative features  616 . The stamp  612  is then used to pattern a photoresist material  618  which is deposited over a substrate  620 . As shown in  FIG. 6E , a mask  624  is positioned between the stamp  612  and a UV light source  626 . In operation, the mask  624  prevents UV light from reaching the portions, shown as uncured portions  630 , of the photoresist material  618  that will be imprinted with the features  616 . The unmasked portions of the photoresist material  618  are cured, shown as cured portions  628 . The cured portions  628  correspond to the areas of the seam  606  and periphery. The stamp  612  then imprints the uncured portions  630  of the photoresist material  618  while the cured portions  628  are not imprinted, as shown in  FIG. 6F , to form a final product  622 , such as a large area substrate, without a seam. 
     The stamp material  610  is generally any suitable material. In one example, the stamp material  610  is a PDMS material. The photoresist material  618  is generally any suitable photoresist material. The substrate  620  is generally any suitable substrate material, including but not limited to, glass, PMMA, and polycarbonate. 
     In another embodiment, the seam  606  is overfilled with a filler material, such as a polymer, and a high elasticity stamp material  610  is used. Further embodiments also contemplate using a maskless direct write laser system to cure the seam  606  and periphery regions before imprint. For example, the maskless direct write laser system is used to cure the seam  606  and periphery regions before the stamp  612  imprints the uncured portions  630  of the photoresist material  618 . Additionally, the maskless direct write laser system can be used to cure the rest of the photoresist material  618  after the imprinting has occurred. 
     The disclosed methods and apparatus are beneficially used to pattern nanoscale features on large area substrates, such as 300 nanometer (nm) or greater display devices, with reduced or eliminated patterning issues at the seams and periphery. For example, the disclosed methods and apparatus can be used imprint a display device with nanofeatures, such as 100 nm features or 50 nm features, with reduced or eliminated patterning issues at the seams and periphery. The disclosed methods and apparatus are useful to pattern Liquid Crystal Displays (LCDs), Light Guide Plates (LGPs), Light Field Plates (LFPs), and Wire Grid Polarizers (WGPs), in addition to other display devices and other optical elements or films for other applications including automotive applications, or augmented reality or virtual reality headsets or smart windows. By reducing or eliminating the patterning irregularities at the seams and periphery, the functionality of the optical device is generally improved. For example, in an LGP, reducing or eliminating the irregularities at the seam and periphery will reduce the light loss from the device. In an LCD, reducing or eliminating the irregularities at the seam and periphery will improve the quality of the projected image from the display and viewers will not see the patterned seams in the image being projected. 
     While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.