Abstract:
Provided is a method of fabricating a wire grid polarizer, the method comprising an organic light-emitting display panel. According to an aspect of the present disclosure, there is provided a method comprising sequentially stacking a conductive wire pattern layer, a first neutral layer, a guide pattern layer and a second neutral layer on a substrate, forming etch-stop patterns on the second neutral layer, forming second neutral layer patterns and guide patterns by patterning the second neutral layer and the guide pattern layer using the etch-stop patterns, coating a block copolymer of two types of monomer blocks having different etch rates on the first neutral layer and the second neutral layer patterns, aligning the block copolymer, removing one type of monomer blocks from the aligned block copolymer, and patterning the conductive wire pattern layer using the remaining monomer blocks, the second neutral layer patterns, and the guide patterns.

Description:
This application claims priority from Korean Patent Application No. 10-2014-0156195 filed on Nov. 11, 2014 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Related Field 
     The present disclosure relates to a wire grid polarizer and a method of fabricating the same. 
     2. Description of the Related Art 
     A wire grid polarizer is an array of conductive wires arranged in parallel such that it polarizes incident light. That is, the wire grid polarizer transmits light having a specific polarization. 
     If the wire grid polarizer has a structure in which the distance between the conductive wires is shorter than the wavelength of incident light, the wire grid polarizer reflects portions of the incident light that have a polarization parallel to the wires and transmits portions of the incident light that have a polarization perpendicular to the wires. Thus, the wire grid polarizer allows reuse of the reflected polarized light, unlike an absorptive polarizer. 
     SUMMARY 
     Aspects of the present disclosure provide a method of fabricating uniform wire grid patterns, a wire grid polarizer fabricated using the method, and a display device including the wire grid polarizer. 
     However, aspects of the present disclosure are not restricted to disclosed herein. The above and other aspects of the present disclosure will become more apparent to one of ordinary skill in the art to which the present disclosure pertains by referencing the detailed description of the present disclosure given below. 
     According to an aspect of the present disclosure, there is provided a method of fabricating a wire grid polarizer, the method comprising sequentially stacking a conductive wire pattern layer, a first neutral layer, a guide pattern layer and a second neutral layer on a substrate, forming etch-stop patterns on the second neutral layer, forming second neutral layer patterns and guide patterns by patterning the second neutral layer and the guide pattern layer using the etch-stop patterns, coating a block copolymer of two types of monomer blocks having different etch rates on the first neutral layer and the second neutral layer patterns, aligning the block copolymer, removing one type of monomer blocks from the aligned block copolymer, and patterning the conductive wire pattern layer using the remaining monomer blocks, the second neutral layer patterns, and the guide patterns. 
     According to another aspect of the present disclosure, there is provided a method of fabricating a wire grid polarizer, the method comprising sequentially stacking a conductive wire pattern layer and a guide pattern layer on a substrate, forming guide patterns by patterning the guide pattern layer, forming a neutral layer on the guide patterns and the conductive wire pattern layer, coating a block copolymer of two types of monomer blocks having different etch rates on the neutral layer, aligning the block copolymer, removing one type of monomer blocks from the aligned block copolymer, and patterning the conductive wire pattern layer using the remaining monomer blocks, the neutral layer, and the guide patterns. 
     According to still another aspect of the present disclosure, there is provided a wire grid polarizer comprising a substrate, a plurality of parallel conductive wire patterns protruding from the substrate, and a plurality of neutral layer patterns located on one or more of the conductive wire patterns. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects and features of the present disclosure will become more apparent when the detailed description of exemplary embodiments provided below is considered in conjunction with the following drawings, in which: 
         FIGS. 1, 2, 3, 4, 5, 6 and 7  are cross-sectional views illustrating the steps of a process of fabricating a wire grid polarizer according to an embodiment of the present system and method; 
         FIG. 8  is a vertical cross-sectional view of a wire grid polarizer according to another embodiment of the present system and method; 
         FIG. 9  is a vertical cross-sectional view of a wire grid polarizer according to another embodiment of the present system and method; 
         FIG. 10  is a vertical cross-sectional view of a wire grid polarizer according to another embodiment of the present system and method; 
         FIGS. 11, 12, 13, 14, 15, 16, 17 and 18  are cross-sectional views illustrating the steps of a process of fabricating a wire grid polarizer according to another embodiment of the present system and method; and 
         FIG. 19  is a vertical cross-sectional view of a wire grid polarizer according to another embodiment of the present system and method. 
     
    
    
     DETAILED DESCRIPTION 
     The aspects and features of the present system and method will be apparent by referring to the embodiments provided herein with reference to the accompanying drawings. However, the present system and method are not limited to the embodiments disclosed hereinafter, but can be implemented in diverse forms. The matters defined in the description, such as the detailed construction and elements, are provided to assist those of ordinary skill in the art in understanding the present system and method, and therefore, are not limiting of the present system and method. The same reference numerals are used herein to describe the same elements across various figures. In the drawings, the sizes and relative sizes of the layers and areas may be exaggerated for clarity. 
     The term “on” that is used to designate that an element is on another element or a layer includes both a case in which the element is located directly on the other element or layer and a case in which the element is located on the other element with an intervening element or layer in between the element and the other element. 
     Although the terms “first, second, and so forth” are used to describe diverse constituent elements, such constituent elements are not limited by the terms. The terms are used only to distinguish a constituent element from another constituent element. Accordingly, in the following description, a first constituent element may also be referred to as a second constituent element. 
     Exemplary embodiments are described hereinafter with reference to the accompanying drawings. 
       FIGS. 1 through 7  are cross-sectional views illustrating the steps of a process of fabricating a wire grid polarizer according to an embodiment of the present system and method. 
     Referring to  FIG. 1 , a conductive wire pattern layer  120 , a first neutral layer  131 , a guide pattern layer  140 , a second neutral layer  132 , and an etch-stop layer  150  may be sequentially stacked on a substrate  110 . 
     The substrate  110  may be made of a material that transmits visible light. The material that forms the substrate  110  may be selected according to use or process. Examples of the material may include various polymers such as, but not limited to, glass, quartz, acrylic, triacetylcellulose (TAC), cyclic olefin copolymer (COP), cyclic olefin polymer (COC), polycarbonate (PC), polyethylene naphthalate (PET), polyimide (PI), polyethylene naphthalate (PEN), polyether sulfone (PES), and polyarylate (PAR). The substrate  110  may be made of a flexible, optical film material. 
     The conductive wire pattern layer  120  may be made of a conductive material. In an exemplary embodiment, the conductive wire pattern layer  120  may be made of a metal material, such as one selected from the group consisting of, but not limited to, aluminum (Al), chrome (Cr), silver (Ag), copper (Cu), nickel (Ni), titanium (Ti), cobalt (Co), molybdenum (Mo), or an alloy of these metals. 
     In some cases, the conductive wire pattern layer  120  may include two or more layers. For example, a first conductive wire pattern layer (not illustrated) may be made of aluminum, and a second conductive wire pattern layer (not illustrated) may be made of titanium. However, the present system and method are not limited thereto. If the first conductive wire pattern layer (not illustrated) is made of aluminum, hillocks may form depending on the temperature used in a subsequent process. If hillocks do form, the upper surface of the first conductive wire pattern layer may become uneven, resulting in a product with degraded optical characteristics. To prevent hillocks from forming, the second conductive wire pattern layer (not illustrated) made of titanium is formed on the first conductive wire pattern layer (not illustrated). Therefore, hillocks that may otherwise form due to a subsequent process are prevented. 
     The conductive wire pattern layer  120  may be formed using, but not limited to, a general sputtering method, a chemical vapor deposition (CVD) method, or an evaporation method. 
     For the alignment of a block copolymer  160  in a subsequent process, each of the first neutral layer  131  and the second neutral layer  132  may be made of a material that has similar surface energy as that of the block copolymer  160 . For example, each of the first neutral layer  131  and the second neutral layer  132  may be, but is not limited to, a random copolymer of monomers of the block copolymer  160 . The random copolymer may be, e.g., a cross-linkable random copolymer. 
     The guide pattern layer  140  may be a soft pattern layer made of photoresist or organic matter or a hard pattern layer made of metal or inorganic matter. 
     The etch-stop layer  150  may be made of a negative photoresist or positive photoresist. 
     Referring to  FIGS. 2 and 3 , second neutral layer patterns  132   a  and guide patterns  140   a  may be formed. In an example, the etch-stop layer  150  may be exposed to light and developed using a mask to form etch-stop patterns  150   a . Then, the second neutral layer  132  and the guide pattern layer  140  may be etched to form the second neutral layer patterns  132   a  and the guide patterns  140   a.    
     In another example, the guide pattern layer  140  may be a polarity switchable photoresist. In such case, after the guide pattern layer  140  is coated, the polarity of the guide pattern layer  140  can be changed by a curing process. This allows portions of the guide pattern layer  140  corresponding to regions of the etch-stop layer  150  that are removed by a developing solution to also be removed. However, the guide pattern layer  140  has a tolerance to a solvent used to strip the etch-stop patterns  150   a . Therefore, the guide patterns  140   a  may be formed. 
     In a more specific example, an acrylate-based polarity switchable photoresist may be coated to form the guide pattern layer  140  and then cured by light exposure or heat treatment. As a result, the acrylate-based polarity switchable photoresist of the guide pattern layer  140  can be developed in tetramethylammonium hydroxide (TMAH) but may have a tolerance to a general organic solvent. The material that forms the guide pattern layer  140  is not limited to the above example. Any polarity switchable photoresist material may be used. 
     Referring to  FIG. 4 , the block copolymer  160  of two types of monomers having different etch rates may be formed on the first neutral layer  131  and the second neutral layer patterns  132   a . The block copolymer  160  may be, but is not limited to, a polystyrene (PS)-polymethyl methacrylate (PMMA) block copolymer. 
     Referring to  FIG. 5 , the block copolymer  160  may be phase-separated into monomer blocks  161  and  162 . The monomer blocks  161  and  162  of the block copolymer  160  may be made of hydrophilic and hydrophobic materials having different etch rates. Accordingly, the first neutral layer  131  and the second neutral layer patterns  132   a  may be formed on bottom portions of the monomer blocks  161  and  162 , thus effectively aligning the block copolymer  160 . 
     In one example, the side surfaces of the guide patterns  140   a  may have selectivity for any one of the monomer blocks  161  and  162 . More specifically, the side surfaces of the guide patterns  140   a  may be hydrophilic or hydrophobic. This would allow the block copolymer  160  to be aligned more effectively. 
     The block copolymer  160  may be aligned by, but not limited to, thermal annealing or solvent annealing. Generally, solvent annealing, which is performed in a chamber including an evaporated solvent, has reduced alignment time compared with thermal annealing in which heat is applied. Whether solvent annealing or thermal annealing is used may be selected according to the layout of the entire process. 
     Referring to  FIG. 6 , the monomer blocks  162  having a relatively high etch rate may be removed. To remove the monomer blocks  162  having a relatively high etch rate, a conventional etching process may be used. For example, a dry etching process may be used, but the present system and method are not limited thereto. A gas for use in the above etching process may be, but is not limited to, one or more selected from the group consisting of 02, carbon fluoride gas, and hydrogen fluoride (HF). The carbon fluoride gas may be, but is not limited to, one or more selected from the group consisting of C 4 F 8 , CHF 3 , CH 2 F 2 , CF 4  and C 2 F 6 . 
     Referring to  FIG. 7 , the conductive wire pattern layer  120  may be etched using the monomer blocks  161  having a relatively low etch rate and the guide patterns  140   a  as a mask. Accordingly, a plurality of parallel conductive wire patterns  120   a  protruding from the substrate  110  may be formed. 
     The wire grid polarizer fabricated as described above includes the substrate  110 , a plurality of parallel conductive wire patterns  120   a  protruding from the substrate  110 , the first neutral layer patterns  131   a , and the guide patterns  140   a  located on one or more of the conductive wire patterns  120   a . For example, first neutral layer patterns  131   a  not exposed by the guide patterns  140   a  may be located on the conductive wire patterns  120   a  together with the guide patterns  140   a , and first neutral layer  131  exposed between the guide patterns  140   a  may be removed by etching. 
     As  FIG. 7  illustrates, the first neutral layer patterns  131   a  and the guide patterns  140   a  may be repeatedly arranged at intervals. Specifically, a plurality of pairs of the first neutral layer patterns  131   a  and the guide pattern  140   a  may be disposed adjacent to each other and may be repeatedly arranged between groups of one or more conductive wire patterns  120   a  without the first neutral layer patterns  131   a  and the guide patterns  140   a  thereon. 
       FIG. 8  is a vertical cross-sectional view of a wire grid polarizer according to another embodiment of the present system and method. Referring to  FIG. 8 , the wire grid polarizer includes a substrate  110 , a plurality of parallel conductive wire patterns  120   a  protruding from the substrate  110 , first neutral layer patterns  131   a  located on the conductive wire patterns  120   a , and guide patterns  140   a  located on one or more of the first neutral layer patterns  131   a.    
     The guide patterns  140   a  may be repeatedly arranged at intervals. Specifically, as  FIG. 8  shows, the guide patterns  140   a  may be disposed adjacent to each other and may be repeatedly arranged between groups of one or more pairs of the conductive wire pattern  120   a  and the first neutral layer pattern  131   a  without the guide pattern  140   a  thereon. 
     The wire grid polarizer may be fabricated as a result of forming the first neutral layer patterns  131   a  by etching a first neutral layer  131  exposed between the guide patterns  140   a . Although not illustrated in the drawing, in some cases, monomer blocks  161  having a relatively low etch rate may remain on first neutral layer patterns  131   a  without the guide patterns  140   a  thereon. 
       FIG. 9  is a vertical cross-sectional view of a wire grid polarizer according to another embodiment of the present system and method. Referring to  FIG. 9 , the wire grid polarizer includes a substrate  110 , a plurality of parallel conductive wire patterns  120   a  protruding from the substrate  110 , and first neutral layer patterns  131   a  located on one or more of the conductive wire patterns  120   a.    
     In this case, the first neutral layer patterns  131   a  may be repeatedly arranged at intervals. Specifically, the first neutral layer patterns  131   a  may be disposed adjacent to each other and may be repeatedly arranged between groups of one or more conductive wire patterns  120   a  without the first neutral layer patterns  131   a  thereon. 
     The wire grid polarizer may be fabricated as a result of removing guide patterns  140   a  and portions of a first neutral layer  131  exposed between the guide patterns  140   a  using an etching process and leaving the first neutral layer patterns  131   a  not exposed by the guide patterns  140   a  on the conductive wire patterns  120   a.    
       FIG. 10  is a vertical cross-sectional view of a wire grid polarizer according to another embodiment of the present system and method. Referring to  FIG. 10 , the wire grid polarizer includes a substrate  110  and a plurality of parallel conductive wire patterns  120   a  protruding from the substrate  110 . In this case, first neutral layer patterns  131   a , guide patterns  140   a , and monomer blocks  161  having a relatively low etch rate may be removed from the conductive wire patterns  120   a  by a strip process. However, if the first neutral layer patterns  131   a , the guide patterns  140   a , and the monomer blocks  161  having a relatively low etch rate are removed by etching, the conductive wire patterns  120   a  may be damaged due to the difference in etch rates of these materials. 
       FIGS. 11 through 18  are cross-sectional views illustrating the steps of a process of fabricating a wire grid polarizer according to another embodiment of the present system and method. 
     Referring to  FIG. 11 , a conductive wire pattern layer  120 , a guide pattern layer  140 , and an etch-stop layer  150  may be sequentially stacked on a substrate  110 . The conductive wire pattern layer  120 , the guide pattern layer  140  and the etch-stop layer  150  stacked on the substrate  110  are identical to those described above with reference to  FIG. 1 , and thus a redundant description thereof is omitted. 
     Referring to  FIGS. 12 and 13 , guide patterns  140   a  may be formed. 
     In one example, the etch-stop layer  150  may be exposed to light and developed using a mask to form etch-stop patterns  150   a . Then, the guide pattern layer  140  may be etched to form the guide patterns  140   a.    
     In another example, the guide pattern layer  140  may be a polarity switchable photoresist. In such case, after the guide pattern layer  140  is coated, the polarity of the coated guide pattern layer  140  may be changed by a curing process. This allows portions of the guide pattern layer  140  corresponding to regions of the etch-stop layer  150  that are removed by a developing solution to also be removed. However, the guide pattern layer  140  has a tolerance to a solvent used to strip the etch-stop patterns  150   a . Therefore, the guide patterns  140   a  may be formed. 
     In a more specific example, an acrylate-based polarity switchable photoresist may be coated to form the guide pattern layer  140  and then cured by light exposure or heat treatment. As a result, the acrylate-based polarity switchable photoresist of the guide pattern layer  140  can be developed in TMAH but may have a tolerance to a general organic solvent. The material that forms the guide pattern layer  140  is not limited to the above example. Any polarity switchable photoresist material may be used. 
     Referring to  FIG. 14 , a neutral layer  130  may be formed on the conductive wire pattern layer  120  and the guide patterns  140   a . In this case, the neutral layer  130  may be coated only on the upper surface of the conductive wire pattern layer  120  and the upper surfaces of the guide patterns  140   a . In some cases, after the neutral layer  130  is coated, it may be cross-linked. 
     The neutral layer  130  is identical or corresponds to the first and second neutral layers  131  and  132  described above with reference to  FIG. 1 , and thus a redundant description thereof is omitted. 
     Referring to  FIG. 15 , a block copolymer  160  of two types of monomers having different etch rates may be formed on the entire neutral layer  130 . Later, the block copolymer  160  may be phase-separated into monomer blocks  161  and  162 . 
     The block copolymer  160  may be, but is not limited to, a polystyrene (PS)-polymethyl methacrylate (PMMA) block copolymer. 
     Referring to  FIG. 16 , the block copolymer  160  may be phase-separated into the monomer blocks  161  and  162 . The monomer blocks  161  and  162  of the block copolymer  160  may be made of hydrophilic and hydrophobic materials having different etch rates. Accordingly, the neutral layer  130  may be formed on bottom portions of the monomer blocks  161  and  162 , thus effectively aligning the block copolymer  160 . 
     In one example, the side surfaces of the guide patterns  140   a  may have selectivity for any one of the monomer blocks  161  and  162 . More specifically, the side surfaces of the guide patterns  140   a  may be hydrophilic or hydrophobic. This would allow the block copolymer  160  to be aligned more effectively. 
     The block copolymer  160  may be aligned by, but not limited to, thermal annealing or solvent annealing. Generally, solvent annealing, which is performed in a chamber including an evaporated solvent, has a reduced alignment time compared with thermal annealing in which heat is applied. Whether solvent annealing or thermal annealing is used may be selected according to the layout of the entire process. 
     Referring to  FIG. 17 , the monomer blocks  162  having a relatively high etch rate may be removed. To remove the monomer blocks  162  having a relatively high etch rate, a conventional etching process may be used. For example, a dry etching process may be used, but the present system and method are not limited thereto. A gas for use in the above etching process may be, but is not limited to, one or more selected from the group consisting of 02, carbon fluoride gas, and hydrogen fluoride (HF). The carbon fluoride gas may be, but is not limited to, one or more selected from the group consisting of C 4 F 8 , CHF 3 , CH 2 F 2 , CF 4  and C 2 F 6 . 
     Referring to  FIG. 18 , the conductive wire pattern layer  120  may be etched using the monomer blocks  161  having a relatively low etch rate and the guide patterns  140   a  as a mask. Accordingly, a plurality of parallel conductive wire patterns  120   a  protruding from the substrate  110  may be formed. 
     The wire grid polarizer fabricated as described above includes the substrate  110 , a plurality of parallel conductive wire patterns  120   a  protruding from the substrate  110 , and the guide patterns  140   a  located on one or more of the conductive wire patterns  120   a.    
     In this case, the guide patterns  140   a  may be repeatedly arranged at intervals. Specifically, the guide patterns  140   a  may be disposed adjacent to each other and may be repeatedly arranged between groups of one or more conductive wire patterns  120   a  without the guide patterns  140   a  thereon. 
       FIG. 19  is a vertical cross-sectional view of a wire grid polarizer according to another embodiment of the present system and method. Referring to  FIG. 19 , the wire grid polarizer includes a substrate  110 , a plurality of parallel conductive wire patterns  120   a  protruding from the substrate  110 , and neutral layer patterns  130   a  and guide patterns  140   a  located selectively on the conductive wire patterns  120   a.    
     In this case, the neutral layer patterns  130   a  and the guide patterns  140   a  may be repeatedly arranged at intervals. Specifically, the guide patterns  140   a  may be disposed adjacent to each other and may be repeatedly arranged between groups of one or more neutral layer patterns  130   a . In addition, the neutral layer patterns  130   a  may be disposed adjacent to each other and may be repeatedly arranged between groups of one or more guide patterns  140   a.    
     The wire grid polarizer may be fabricated as a result of forming the neutral layer patterns  130   a  by etching a neutral layer  130  exposed between the guide patterns  140   a . Although not illustrated in the drawing, in some cases, monomer blocks  161  having a relatively low etch rate may remain on the neutral layer patterns  130   a.    
     The wire grid polarizer of the present system and method may be used in a display device. The display device may be, but is not limited to, a liquid crystal display (LCD), an organic light-emitting diode display (OLED), etc. 
     In this case, the wire grid polarizer may be used as an in-cell polarizer by forming a non-conductive protective layer on the conductive wire patterns  120   a  and then forming wiring and a thin-film transistor on the protective layer. 
     Embodiments of the present system and method provide at least one of the following advantages. 
     A wire grid polarizer having superior optical characteristics is provided. 
     However, the effects of the present system and method are not restricted to those discussed herein. The above and other effects of the present system and method will become more apparent to one of ordinary skill in the art to which the present system and method pertain.