Patent Publication Number: US-2023152689-A1

Title: Wire grid polarizer and manufacturing method thereof

Description:
FIELD OF THE INVENTION 
     The invention relates to a method for manufacturing a wire grid polarizer, and more particularly to a manufacturing method for a wire grid polarizer with an additive process by nanoimprinting, electroforming, or electrodeless plating technology. 
     BACKGROUND OF THE INVENTION 
     Wire grid polarizer (WGP) has better extinguish ratio and view angle than traditional polarizers. General polarizers containing plastic materials that are not resistant to high temperatures will reduce or lose their polarization performance at 100° C. Therefore, wire grid polarizer is more suitable to be applied to high-end display devices, projectors, light sensors, ambient light sensors (ALS), image detection, face recognition and gesture recognition, automotive Lidar imaging and range detection system, 3D face recognition system of Time of Flight (TOF). 
     The wire grid size of the wire grid polarizer is approximately ½˜⅕ of the wavelength of the applied light wave band. If the applied light wave band is the visible light wave band (400 nm˜700 nm), the pitch of the wire grid is approximately close to 100 nm, and the line width of the wire grid is about 50 nm; if the applied light wave band is in the ultraviolet (UV) range, the line width of the wire grid is below 20 nm. Therefore, the requirements for precision in production are very high. 
     The manufacturing methods of the conventional wire grid polarizer can be found in U.S. Pat. Nos. 10,353,127 B2, 10,983,389 B2, 10,114,161 B2, and 9,488,765 B2, wherein the wire grids need to be formed by a expensive lithography equipment, such as electron beam (e-beam), ion-beam, extreme ultraviolet (EUV), dual UV-Beam interference or X-Ray exposure sources. Accordingly, the manufacturing method of extremely fine and low defect density wire grids requires proceeding in high precision and being performed repeatedly, resulting in a high cost, and hard to be applicable. 
     SUMMARY OF THE INVENTION 
     The invention provides a manufacturing method for a wire grid polarizer comprising following steps of: providing a substrate; forming a conductive layer on the substrate; forming an inverted wire grid structure on the conductive layer, wherein the inverted wire grid structure comprises a plurality of ridges and a plurality of trenches disposed alternately with the plurality of ridges, and the conductive layer is exposed at the plurality of trenches; and depositing a metal on the inverted wire grid structure formed on the conductive layer to form a wire grid structure; wherein the metal is deposited by an electroplating, an electroforming, or an electrodeless plating process. 
     The invention further provides a wire grid polarizer comprising: a substrate; a conductive layer formed on the substrate; and a wire grid structure formed on the conductive layer, wherein the wire grid structure is deposited on the conductive layer by an electroplating, an electroforming, or an electrodeless plating process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A- 1 I  are schematic diagrams of the steps of a manufacturing method according to a first embodiment of the invention. 
         FIG.  2    is a schematic diagram of a wire grid polarizer according to first embodiment of the invention. 
         FIG.  3    is a schematic diagram according to a second embodiment of the invention. 
         FIG.  4    is a schematic diagram according to a third embodiment of the invention. 
         FIG.  5    is a schematic diagram according to a fourth embodiment of the invention. 
         FIG.  6    is a schematic diagram according to a fifth embodiment of the invention. 
         FIG.  7    is a schematic diagram according to a sixth embodiment of the invention. 
         FIG.  8    is a schematic diagram according to a seventh embodiment of the invention. 
         FIG.  9    is a schematic diagram according to an eighth embodiment of the invention. 
         FIG.  10    is a schematic diagram according to a ninth embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description provides several different embodiments or examples to illustrate different features of the invention. The description provides specific examples of each component and its disposition mode, but these specific examples are not intended to limit the invention. For example, if it is described below that a first feature is formed on or above a second feature, it means that the first feature may directly contact with the second feature, or the first feature may not contact with the second feature since additional features are formed between the first feature and the second feature. In addition, the different embodiments described below may repeatedly use the same reference symbols and/or marks for the purpose of simplifying the description, but it is not used to limit the specific relationship between the different embodiments and/or structures. 
     In the specification, although some embodiments execute the steps in a specific order, the steps may be executed in another reasonable order. For different embodiments, certain features described below can be replaced or eliminated. It should be understood that some additional operations can be performed before, during, or after the method, and in other embodiments of the method, some operations can be replaced or omitted. 
     In this specification, the terms used in the description of various embodiments are only for the purpose of describing specific examples, and are not intended to limit the invention. Unless the context clearly indicates otherwise, or deliberately limits the quantity of elements, the singular forms “a”, “an” and “the” used herein also include plural forms. 
     Please refer to  FIG.  1 A ,  FIG.  1 B ,  FIG.  1 C ,  FIG.  1 D ,  FIG.  1 E ,  FIG.  1 F ,  FIG.  1 G ,  FIG.  1 H  and  FIG.  1 I , which show the steps of a manufacturing method according to a first embodiment of the invention. As shown in  FIG.  1 A , a substrate  10  is first provided. In this embodiment, the substrate  10  is transparent to the light wave band of the application. If the substrate  10  is made of one of materials selected from quartz, optical glass (such as BK7 glass, soda glass, boron glass, alkali-free glass, aluminosilicate glass, borosilicate glass, but is not limited thereto), sapphire, silicon dioxide (SiO 2 ), silicon nitride (SiN x ), aluminium oxide (Al 2 O 3 ), zirconium dioxide (ZrO 2 ), aluminium nitride (AlN x ), gallium nitride (GaN), gallium arsenide (GaAs) and indium phosphide (InP), the substrate  10  is transparent to ultraviolet, visible, near-infrared, infrared, far-infrared wave bands. If the substrate  10  is made of one of materials selected from silicon (Si) and silicon carbide (SiC), the substrate  10  is transparent to near-infrared, infrared and far-infrared wave bands. If the substrate  10  is made of one of materials selected from high molecular plastics (such as polycarbonate (PC), COP (Cyclo Olefin Polymer), polyimide (PI), polyethylene terephthalate (PET), triacetate (TAC), polyethylene naphthalate (PEN)), the substrate  10  is transparent to visible, near-infrared, infrared, and far-infrared wave bands. In addition, the substrate  10  can also be coated or bonded with thermal release adhesive or UV release adhesive to facilitate removal of the substrate  10  if necessary, or transfer of a component to another substrate or component to reduce an overall thickness of the component. 
     As shown in  FIG.  1 B , a conductive layer  20  is formed on an upper surface  11  of the substrate  10 . The conductive layer  20  is used to form a wire grid structure. The conductive layer  20  is made of a metal material (thickness less than 100 nm), a metal oxide material (thickness less than 500 nm), or a non-oxide material (thickness less than 500 nm). For example, the metal material can be a pure metal such as gold (Au), silver (Ag), copper (Cu), nickel (Ni), aluminum (Al), platinum (Pt), or an alloy thereof. The metal oxide material can be tin dioxide (SnO 2 ), indium oxide (In 2 O 3 ), cadmium oxide (CdO), zinc oxide (ZnO), titanium dioxide (TiO 2 ), a mixture (SnO 2 —Sb) of tin dioxide and antimony, a mixture (SnO 2 —WO 3 ) of tin dioxide and tungsten oxide, a mixture (In 2 O 3 —SnO 2 , ITO) of indium oxide and tin oxide, a mixture (In 2 O 3 —ZnO, IZO) of indium oxide and zinc oxide, a mixture (In 2 O 3 —Sb 2 O 3 ) of indium oxide and antimony oxide, a mixture (In 2 O 3 —WO 3 ) of indium oxide and tungsten oxide, a mixture (SnO 2 —F) of tin dioxide and fluorine, a mixture (In 2 O 3 —Al) of indium oxide and aluminum, a mixture (ZnO—Al, AZO) of zinc oxide and aluminum, gallium zinc oxide (GaZnO, GZO), indium gallium zinc oxide (InGaZnO, IGZO) or a combination of at least two of the above-mentioned metal oxides. The non-oxide material of the conductive layer  20  can be lanthanum hexaboride (LaB 6 ), titanium nitride (TiN), cadmium sulfide (CdS). 
     To manufacture a transmission type wire grid polarizer, the substrate  10  and the conductive layer  20  should be made of a material which is transparent to the light wave band of the application. To manufacture a reflective wire grid polarizer, both the substrate  10  and the conductive layer  20  can be made of an opaque material. Alternatively, either the substrate  10  or the conductive layer  20  can be made of a material which is transparent to the light wave band of the application, and another is made of the opaque material. 
     In one embodiment, the conductive layer  20  is a single layer from any one of the metal, the metal oxide, and the non-oxide, and can also be a single layer, a double layer or a multilayer of a mixture from any two of the metal, the metal oxide, and the non-oxide or a mixture of the metal, the metal oxide, and the non-oxide, such as TiO 2 /Ag/TiO 2 , SnO 2 /Ni/SnO 2 , Bi 2 O 3 /Au/Bi 2 O 3 , Pt/SnO 2 , SnO 2 /Au/SnO 2 . 
     Then, an inverted wire grid structure is formed on the conductive layer  20  to serve as a mold for forming the wire grid structure. In the invention, processes such as laser interference lithography, e-beam lithography, ion-beam lithography, extreme ultraviolet (EUV) lithography, X-ray lithography, photo-lithography, or nano-imprint lithography can be used to form the inverted wire grid structure, but the invention is not limited thereto. Among the lithography techniques listed above, the nano-imprint lithography has a lower production cost. Specifically, most of the lithography techniques require an electron beam lithography (EBL) equipment to form the inverted wire grid structure; however, the cost of the EBL equipment is high, and it takes a long manufacturing time for the EBL equipment to form the inverted wire grid structure on the large-area wire grid polarizer (for example, it takes about 3 to 4 days to manufacture on a single six-inch wafer). Thus, the lithography techniques implemented by the EBL equipment are disadvantageous for commercial applications since their mass production capacities are low. On the contrary, the nano-imprint lithography is able to form the inverted wire grid structure on a large-area nano-imprint resist layer by only one-time imprinting, thereby the nano-imprint lithography can be implemented by low cost equipment and has a rapid manufacturing time. Accordingly, the following steps of the invention for forming the inverted wire grid are illustrated by using the nano-imprint lithography. 
     As shown in  FIG.  1 C , a nano-imprint resist layer  30  is formed on the conductive layer  20 . The nano-imprint resist layer  30  can be formed by spin coating or spray coating, but the invention is not limited thereto. The nano-imprint resist layer  30  can be made of a thermal curable polymer resin or a UV-curable polymer resin, such as acrylic-based or epoxy-based polymer material. In  FIG.  1 D , a nano-imprint lithography process is performed on the nano-imprint resist layer  30  by a stamp  40 , and the stamp  40  is used as a transfer printing element and has a specific pattern which comprises a plurality of protrusions  41  and a plurality of recesses  42 . 
     Further, the stamp  40  is imprinted on the nano-imprint resist layer  30  after being aligned therewith. As shown in  FIG.  1 E , the specific pattern is transferred onto the nano-imprint resist layer  30 . The specific pattern of the stamp  40  corresponds to the wire grid structure. As shown in  FIG.  1 F , an inverted wire grid structure  30   a  is formed on the nano-imprint resist layer  30  after imprinting. The inverted wire grid structure  30   a  comprises a plurality of ridges  31  and a plurality of trenches  32 , respectively extending in one direction (an axial direction into the paper as shown in  FIG.  1 F ) to form a fin-like structure, and the plurality of ridges  31  and the plurality of trenches  32  are disposed in an alternative manner and are complementary to the wire grid structure. In this example, the nano-imprint resist layer  30  leaves a residual portion  33 . Afterwards, as shown in  FIG.  1 G , the residual portion  33  can be removed by oxygen ashing (O 2 Ashing) or inductively coupled plasma (ICP) through oxygen, but the invention is not limited thereto. An upper surface  21  of the conductive layer  20  is exposed between the plurality of ridges  31 . A fabrication of the inverted wire grid structure  30   a  is completed so far. 
     As shown in  FIG.  1 H , a metal  50  is deposited on the inverted wire grid structure  30   a  on the conductive layer  20 . A manufacturing process of deposition can be electroplating, electroforming or electrodeless plating (also called chemical-plating or autocatalytic plating). The metal  50  can be a metal element or an alloy, such as gold (Au), silver (Ag), copper (Cu), iron (Fe), chromium (Cr), zinc (Zn), nickel (Ni), aluminum (Al), titanium (Ti), tin (Sn), platinum (Pt), palladium (Pd), brass (alloy of copper and Zinc), nickel-gold  5  alloy, or nickel-boron alloy (NiB), but the invention is not limited thereto. The metal  50  is formed between the plurality of ridges  31  to form a wire grid structure  50   a . Then, the inverted wire grid structure  30   a  can be removed by oxygen ashing (O 2 Ashing) or inductively coupled plasma (ICP) through oxygen to obtain a wire grid polarizer, as shown in  FIG.  1 I  and  FIG.  2   . 
     In order to improve the optical characteristics, reliability, and packaging structure of the wire grid polarizer, and the selection of materials is considered, the wire grid polarizer will comprise the following structures which will be illustrated by following examples, and the invention is not limited thereto. Please refer to  FIG.  3    for a schematic diagram of a second embodiment of the invention. In this embodiment, after  FIG.  1 H , only part of the inverted grid structure  30   a  is removed, and other part of the nano-imprint resist layer  30  is remained. Please refer to  FIG.  4    for a schematic diagram of a third embodiment of the invention. In this embodiment, after the step of  FIG.  1 H , the nano-imprint resist layer  30  is not removed, and an optical layer  60  is further formed on the wire grid structure  50   a  and the nano-imprint resist layer  30 , the optical layer  60  is a sheet-like structure and is made of a material transparent to the light wave band of the application. The optical layer  60  can be an adhesive used in a packaging process, such as optically clear adhesive (OCA), bonding glue or resin, bonding film, hard coat film, optical adhesive film etc., but the invention is not limited thereto. The optical layer  60  can also be an optical coating made of silicon dioxide (SiO 2 ), silicon nitride (SiN x ), or magnesium fluoride (MgF 2 ), or other similar materials. Alternatively, the optical layer  60  can also be made of the materials of the conductive layer  20  and/or the substrate  10  mentioned above. Thereby, the optical characteristics, reliability, and scratch resistance of the wire grid polarizer can be improved. 
     The optical layer  60  can also be an optical film with specific optical characteristics formed on the wire grid structure  50   a  and the nano-imprint resist layer  30  by coating or bonding to improve or adjust the optical characteristics of the wire grid polarizer. The optical layer  60  can be, for example, band-pass filter, band-stop filter, low-pass filter, high-Pass filter, anti-reflection coating or RGB filter to improve the transmittance and reflectance of a specific wavelength range. 
     Please refer to  FIG.  5    for a schematic diagram of a fourth embodiment of the invention. In this embodiment, after the step of  FIG.  1 I , the optical layer  60  is further formed on the wire grid structure  50   a , and the optical layer  60  comprises a columnar structure  61  filling a recess  50   b  of the wire grid structure  50   a . The optical layer  60  can be silicon dioxide (SiO 2 ), silicon nitride (SiN x ), magnesium fluoride (MgF 2 ), zirconium dioxide (ZrO 2 ), or other materials. The optical layer  60  can also be a transparent adhesive for bonding used in the general component packaging process, such as optically clear adhesive (OCA), protective adhesive, hard coat film, bonding glue or resin, or photoresist, imprint resin, but is not limited thereto. Adding the optical layer  60  can be a requirement for component packaging, or can be used to improve the optical characteristics, reliability, and scratch resistance of the metal optical grating. 
     Please refer to  FIG.  6    for a schematic diagram of a fifth embodiment of the invention. In this embodiment, after the step of  FIG.  1 H , only part of the inverted wire grid structure  30   a  is removed, remaining part of the nano-imprint resist layer  30 , and the optical layer  60  is further formed on the wire grid structure  50   a . The columnar structure  61  of the optical layer  60  fills in the recess  50   b  of the wire grid structure  50   a  and is formed on the nano-imprint resist layer  30 . Please refer to  FIG.  7    for a schematic diagram of a sixth embodiment of the invention. In this embodiment, after the step of  FIG.  1 I , the optical layer  60  is further formed on the wire grid structure  50   a , the optical layer  60  is a sheet-like structure, and no material is filled between the metal  50 . Please refer to  FIG.  8    for a schematic diagram of a seventh embodiment of the invention. In this embodiment, after the step of  FIG.  1 H , only part of the inverted wire grid structure  30   a  is removed, remaining part of the nano-imprint resist layer  30 , and the optical layer  60  is further formed on the wire grid structure  50   a . The optical layer  60  is a sheet-like structure. 
     Please refer to  FIG.  9    for a schematic diagram of an eighth embodiment of the invention. In this embodiment, after the step of  FIG.  1 I , the optical layer  60  is disposed on the wire grid structure  50   a  through a bonding layer  70 . The bonding layer  70  can be an opaque material for packaging, or a low melting metal or alloy for packaging with different substrate materials, such as aluminum (Al), tin (Sb), indium (In), tin gold (AuSb) etc., but the invention is not limited thereto. A material of the bonding layer  70  needs to be matched with the materials of the optical layer  60  and the wire grid structure  50   a . A method of forming the bonding layer  70  is a conventional technology of packaging process, thus it will not be mentioned here again. Please refer to  FIG.  10    for a schematic diagram of a ninth embodiment of the invention. In this embodiment, after the step of  FIG.  1 H , only part of the inverted wire grid structure  30   a  is removed, remaining part of the nano-imprint resist layer  30 , and the optical layer  60  is disposed on the wire grid structure  50   a  through the bonding layer  70 . 
     The optical layer  60  is disposed to match with the wire grid structure  50   a  according to different applications. In addition to the positions shown in the figures, in other embodiments, forming at least one optical layer  60  on the substrate  10 , and the conductive layer  20  is formed on the optical layer  60 , the nano-imprint resist layer  30  is then formed on the conductive layer  20 , and the above-mentioned steps are performed to obtain the wire grid structure  50   a.    
     In the invention, a conductive layer formed on a substrate is used to form an inverted wire grid structure through nano-imprint lithography or other lithography techniques. By utilizing an electric conductivity of the conductive layer, electroplating, electroforming or electrodeless coating can be used to form a wire grid polarizer on the conductive layer, thereby reducing or eliminating the need to use lithography technology and photomask to form a wire grid, and also eliminating the complicated dry etching inductively coupled plasma (ICP) process, making the manufacturing process procedure cheaper and simpler; secondly, after the inverted wire grid structure is formed, the metal is directly deposited to form a wire grid structure, which is an additive process to simplify the production procedure to be capable of greatly reducing the production cost.