Abstract:
A color filter having a bi-layer metal grating is formed by nanoimprint lithography. Nanoimprint lithography, a low cost technology, includes two alternatives, i.e., hotembossing nanoimprint lithography and UV-curable nanoimprint lithography. Manufacture steps comprises providing a substrate with a polymer material layer disposed thereon. A plurality of lands and grooves are formed in the polymer material layer, and a first metal layer and a second metal layer are disposed on the surfaces of the lands and grooves, respectively. Finally, a color filter having a bi-layer metal grating is obtained.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Divisional of co-pending application Ser. No. 11/76,261 filed Jul. 8, 2005, and for which priority is claimed under 35 U.S.C. § 120; and this application claims priority of Application No. 93141344, filed in Taiwan, Republic of China on Dec. 30, 2004, the entire contents of which are hereby incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to a color filter and method of fabricating the same, and more particularly to a color filter having a bi-layer metal grating. 
         [0003]    Color filter, a main component in an LCD device, converts white light to red, green, and blue light. Methods of fabrication comprise dyeing, printing, electrodeposition, or pigment dispersal. Pigment dispersal and dyeing methods are both popularly used. 
         [0004]      FIG. 1  shows a pigment dispersed method, comprising coating of photoresist, pre-baking, exposure, development, and post-baking. A color array, including red, green, and blue films, is formed by repeating the steps three times. The red, green, and blue films have different thicknesses to achieve agreement of light intensity. In addition to being complex and low yield, the method is also limited by low color saturation, non-uniform thickness. 
         [0005]    As well, Dyeing offers only low resistant to heat and chemicals. Neither method significantly improves color purity. 
         [0006]    For a color filter, optical properties, compatibility with subsequent process, and reliability are all priorities, with optical properties such as transmission aid color saturation being most important. 
         [0007]    High transmission requires less intensity from backlight, thereby saving power. Red, green, and blue transmittance percentages are required to approach 85%, 75%, and 75%, respectively. 
         [0008]    High color saturation can be achieved by coupling a color filter with a backlight. The backlight may be a cold cathode fluorescent lamp.  FIG. 2  is a chart showing the transmission spectrum for a cold cathode fluorescent lamp. However, as shown in  FIG. 2 , there are two undesired transmission peaks at 490 nm and 580 nm, resulting in a significant loss of color saturation. In addition, a conventional color filter, as shown in  FIG. 3 , can&#39;t effectively eliminate the described transmitted light. 
         [0009]    Accordingly, a simplified method for fabricating a color filter capable of enhancing color saturation is required. 
       SUMMARY 
       [0010]    A method of fabricating a sub-wavelength structure was proposed by Chou et al. in  1999 , utilizing thermal nanoimprint lithography. In addition, a method of fabricating a nanostructure has been proposed by Molecular Imprints, Inc. using step and flash imprint lithography. 
         [0011]    An embodiment of a method of fabricating a color filter comprises photoresist layers having different thicknesses being formed on a substrate. The substrate is glass or plastic and the photoresist comprises photosensitive polymer material or polymethyl methacrylate (PMMA). 
         [0012]    A mask or mold having suitable period, depth, and aspect ratio is used in hot-embossing nanoimprint lithography or UV-curable nanoimprint lithography, transferring the pattern to the photoresist layers. 
         [0013]    Metal layers are disposed on the photoresist layers by sputtering or vacuum deposition, thereby a bi-layer metal grating with a desired spacing between the metal layers is obtained. The photoresist&#39;s index of refraction exceeds that of the metal layers, reducing reflected light. 
         [0014]    In addition, optical properties of the color filter of the embodiment are simulated by a commercial application, the Gsolver Diffraction Grating Analysis Program, based on RCWA (rigorous coupled wave analysis), a commercial application developed by Grating Solver Development Company. 
         [0015]    The color filter of the embodiment, having a bi-layer metal grating, provides 10 nm spacing between the metal layers, a grating period of 100 to 400 nm, and a thickness of metal layers from 30 to 200 nm. By altering the spacing between the metal layers, grating period, and thickness of metal layers, the problems disclosed can be solved and transmission enhanced up to 85%. 
         [0016]    The bi-layer metal grating of the embodiment has a total thickness of less than 500 nm and difference in metal layers is less than 100 nm. In addition to simplified process the bi-layer metal grating provides smooth surfaces to reduce scattering, with increased brightness. 
         [0017]    The color filter coupled to a polarizer can be used to polarized light and display a color image. The polarizer may be disposed on any side of the substrate. 
         [0018]    The color filter of the embodiment may be applied to reflective, projective, or organic light emitting display devices. 
         [0019]    A detailed description is given in the following embodiments with reference to the accompanying drawings. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0020]    A color filter and method of fabricating the same will become more fully understood from the detailed description given herein below and the accompanying drawings, given by way of illustration only and thus not intended to be limitative of the invention. 
           [0021]      FIG. 1  is a flowchart of a conventional method for fabricating a color filter. 
           [0022]      FIG. 2  is a chart showing the transmission spectrum of a cold cathode fluorescent lamp. 
           [0023]      FIG. 3  is a chart showing the transmission spectrum of a conventional color filter. 
           [0024]      FIGS. 4A to 4G  are cross-sections of an embodiment of a method for fabricating a color filter. 
           [0025]      FIG. 4H  is a cross-section of an embodiment of a color filter. 
           [0026]      FIG. 5  is a chart showing the transmission spectrum of a color filter. 
           [0027]      FIGS. 6A to 6G  are cross-sections of an embodiment of a method for fabricating a color filter. 
           [0028]      FIG. 6H  is a cross-section of an embodiment of a color filter. 
           [0029]      FIG. 7  is a chart showing the transmission spectrum of a color filter. 
           [0030]      FIGS. 8A to 8G  are cross-sections of an embodiment of a method for fabricating a color filter. 
           [0031]      FIG. 8H  is a cross-section of an embodiment of a color filter. 
           [0032]      FIG. 9  is a chart showing the transmission spectrum of a color filter. 
           [0033]      FIGS. 10A to 10G  are cross-sections of an embodiment of a method for fabricating a color filter. 
           [0034]      FIG. 10H  is a cross-section of an embodiment of a color filter. 
           [0035]      FIG. 11  is a chart showing the transmission spectrum of a color filter. 
           [0036]      FIGS. 12A to 12G  are cross-sections of an embodiment of a method for fabricating a color filter. 
           [0037]      FIG. 12H  is a cross-section of an embodiment of a color filter. 
           [0038]      FIG. 13  is a chart showing the transmission spectrum of a color filter. 
           [0039]      FIGS. 14A to 14G  are cross-sections of an embodiment of a method for fabricating a color filter. 
       
    
    
     DETAILED DESCRIPTION  
       [0040]      FIGS. 4 to 13  show embodiments of a method of fabricating a color filter using hot-embossing nanoimprint lithography. 
         [0041]      FIGS. 14A to 14G  show an embodiment of a method of fabricating a color filter using UV-curable nanoimprint lithography. 
         [0042]    In  FIG. 4A , a substrate  410 , such as a glass substrate, with a polymer layer  420  formed thereon is provided. The polymer layer  420  may be polymethyl methacrylate (PMMA). 
         [0043]    In  FIGS. 4A to 4B , a mold  430  having a pattern of microstructure is pressed into the polymer layer  420  and the polymer layer  420  is heated above a glass transition temperature thereof, thereby transferring the pattern to the polymer layer  420 . 
         [0044]    After removal of the mold  430 , a plurality of lands  420   a  and grooves  420   b  are formed in the polymer layer  420 , as shown in  FIG. 4C . 
         [0045]    In  FIG. 4D , reactive ion etching removes residual portions of the polymer layer  420  from the bottom of the grooves  420   b,  thereby exposing surfaces of the substrate  410 . 
         [0046]    In  FIG. 4E , a first metal layer  440   a  and second metal layer  440   b  are concurrently formed on the lands  420   a  and grooves  420   b,  respectively, using sputtering or vacuum deposition. The first metal layer  440   a  and second metal layer  440   b  may be gold (Au). 
         [0047]    In  FIG. 4F , a dielectric layer  450  is formed on the first metal layer  440   a  and second metal layer  440   b.    
         [0048]    In  FIG. 4G , a polarizer  452  is disposed under the substrate  410 . 
         [0049]    In addition, optical properties of the color filter of the embodiment are simulated by a commercial application called Gsolver.  FIG. 5  is a chart showing the transmission spectrum for the color filter shown in  FIG. 4H  with an exemplary incident light  4100 . The incident light  4100  has a wavelength between 400 and 700 nm, and an incident angle  4110 . The substrate  410  has a thickness of 1000 micrometers. One land  420   a  and one groove  420   b  have a total width  480  of 250 nm. The lands  420   a  have a uniform width  470  of 100 nm. The first metal layer  440   a  and second metal layer  440   b  have a uniform thickness  454 , comprising 90, 70, or 65 nm. The first metal layer  440   a  has a relative height  456  exceeding that of the second metal layer  440   b,  of 100, 135, or 160 nm. 
         [0050]    As shown in  FIG. 5 , the transmission peaks occur at 470 (blue), 550 (green), and 610 nm (red), respectively. 
         [0051]    In this embodiment, the color filter provides significantly improved light filtering, thereby increasing the purity of light. 
         [0052]    In  FIG. 6A , a substrate  610 , such as a glass substrate, with a polymer layer  620  formed thereon is provided. The polymer layer  620  may be polymethyl methacrylate (PMMA). 
         [0053]    In  FIGS. 6A to 6B , a mold  630  having a pattern of microstructure is pressed into the polymer layer  620  and the polymer layer  620  is heated above a glass transition temperature thereof, thereby transferring the pattern to the polymer layer  620 . 
         [0054]    After removal of the mold  630 , a plurality of lands  620   a  and grooves  620   b  are formed in the polymer layer  620 , as shown in  FIG. 6C . 
         [0055]    In  FIG. 6D , reactive ion etching removes residual portions of the polymer layer  620  from the bottom of the grooves  620   b,  thereby exposing surfaces of the substrate  610 . 
         [0056]    In  FIG. 6E , a first metal layer  640   a  and second metal layer  640   b  are concurrently formed on the lands  620   a  and grooves  620   b,  respectively, using sputtering or vacuum deposition. The first metal layer  640   a  and second metal layer  640   b  may be aluminum (Al). 
         [0057]    In  FIG. 6F , a dielectric layer  650  is formed on the first metal layer  640   a  and second metal layer  640   b.    
         [0058]    In  FIG. 6G , a polarizer  652  is disposed under the substrate  610 . 
         [0059]    In addition, optical properties of the color filter of the embodiment are simulated by a commercial application called Gsolver.  FIG. 7  is a chart showing the transmission spectrum for the color filter shown in  FIG. 6H  with an exemplary incident light  6100 . The incident light  6100  has a wavelength between 400 and 700 nm, and an incident angle  6110 . The substrate  610  has a thickness of 1000 micrometers. One land  620   a  and one groove  620   b  have a total width  680  of 250 nm. The lands  620   a  have a uniform width  670  of 100 nm. The first metal layer  640   a  and second metal layer  640   b  have a uniform thickness  654 , of 60, 45, or 40 nm. The first metal layer  640   a  has a relative height  656  exceeding that of the second metal layer  640   b,  and the relative height  656  may be 125, 160, or 184 nm. 
         [0060]    As shown in  FIG. 7 , transmission peaks occur at 470 (blue), 550 (green), and 610 nm (red), respectively. 
         [0061]    In this embodiment, the metal layers are Al. The color filter performs better in filtering light and producing high color purity light while the transmission is only about 80%. 
         [0062]    In  FIG. 8A , a substrate  810 , such as a glass substrate, with a polymer layer  820  formed thereon is provided. The polymer layer  820  may be polymethyl methacrylate (PMMA). 
         [0063]    In  FIGS. 8A to 8B , a mold  830  having a pattern of microstructure is pressed into the polymer layer  820  and the polymer layer  820  is heated above a glass transition temperature thereof, thereby transferring the pattern to the polymer layer  820 . 
         [0064]    After removal of the mold  830 , a plurality of lands  820   a  and grooves  820   b  are formed in the polymer layer  820 , as shown in  FIG. 8C . 
         [0065]    In  FIG. 8D , reactive ion etching removes residual portions of the polymer layer  820  from the bottom of the grooves  820   b,  thereby exposing surfaces of the substrate  810 . 
         [0066]    In  FIG. 8E , a first metal layer  840   a  and second metal layer  840   b  are concurrently formed on the lands  820   a  and grooves  820   b,  respectively, using sputtering or vacuum deposition. The first metal layer  840   a  and second metal layer  840   b  may be silver (Ag). 
         [0067]    In  FIG. 8F , a dielectric layer  850  is formed on the first metal layer  840   a  and second metal layer  840   b.    
         [0068]    In  FIG. 8G , a polarizer  852  is disposed under the substrate  810 . 
         [0069]    In addition, optical properties of the color filter of the embodiment are simulated by a commercial application called Gsolver.  FIG. 9  is a chart showing the transmission spectrum for the color filter shown in  FIG. 8H  with an exemplary incident light  8100 . The incident light  8100  has a wavelength between 400 and 700 nm, and an incident angle  8110 . The substrate  810  has a thickness of 1000 micrometers. One land  820   a  and one groove  820   b  have a total width  880  of 250 nm. The lands  820   a  have a uniform width  870  of 100 nm. The first metal layer  840   a  and second metal layer  840   b  have a uniform thickness  854 , of 120, 80, or 80 nm. The first metal layer  840   a  has a relative height  856  exceeding that of the second metal layer  840   b,  of 100, 136, or 160 nm. 
         [0070]    As shown in  FIG. 9 , the transmission peaks occur at 470 (blue), 550 (green), 610 nm (red), respectively. 
         [0071]    In this embodiment, the metal layers are Ag. The color filter not only performs better in filtering light but also produces high color purity light. Additionally. each color light has a transmission over 85%. 
         [0072]    In  FIG. 10A , a substrate  1010 , such as a glass substrate, with a polymer layer  1020  formed thereon is provided. The polymer layer  1020  may be polymethyl methacrylate (PMMA). 
         [0073]    In  FIGS. 10A to 10B , a mold  1030  having a pattern of microstructure is pressed into the polymer layer  1020  and the polymer layer  1020  is heated above a glass transition temperature thereof, thereby transferring the pattern to the polymer layer  1020 . 
         [0074]    After removal of the mold  1030 , a plurality of lands  1020   a  and grooves  1020   b  are formed in the polymer layer  1020 , as shown in  FIG. 10C . 
         [0075]    In  FIG. 10D , reactive ion etching removes residual portions of the polymer layer  1020  from the bottom of the grooves  1020   b,  thereby exposing surfaces of the substrate  1010 . 
         [0076]    In  FIG. 10E , a first metal layer  1040   a  and second metal layer  1040   b  are concurrently formed on the lands  1020   a  and grooves  1020   b,  respectively, using sputtering or vacuum deposition. The first metal layer  1040   a  and second metal layer  1040   b  may be silver (Ag). 
         [0077]    In  FIG. 10F , a dielectric layer  1050  is formed on the first metal layer  1040   a  and second metal layer  1040   b.    
         [0078]    In  FIG. 10G , a polarizer  1052  is disposed under the substrate  1010 . 
         [0079]    In addition, optical properties of the color filter of the embodiment are simulated by a commercial application called Gsolver.  FIG. 11  is a chart showing the transmission spectrum for the color filter shown in  FIG. 10H  with an exemplary incident light  10100 . The incident light  10100  has a wavelength between 400 and 700 nm, and an incident angle  10110 . The substrate  1010  has a thickness of 1000 micrometers. One land  1020   a  and one groove  1020   b  have a total width  1080  of 200 nm. The lands  1020   a  have a uniform width  1070  of 100 nm. The first metal layer  1040   a  and second metal layer  1040   b  have a uniform thickness  1054 , of 50, 60, or 60 nm. The first metal layer  1040   a  has a relative height  1056  exceeding that of the second metal layer  1040   b,  of 100, 133, or 160 nm. 
         [0080]    As shown in  FIG. 11 , the transmission peaks occur at 470 (blue), 550 (green), and 610 nm (red), respectively. 
         [0081]    In this embodiment, each color light has a transmission over 80% when the width  1080  shifts to 200 nm. 
         [0082]    In  FIG. 12A , a substrate  1210 , such as a glass substrate, with a polymer layer  1220  thereon is provided. The polymer layer  1220  may be polymethyl methacrylate (PMMA). 
         [0083]    In  FIGS. 12A to 12B , a mold  1230  having a pattern of microstructure is pressed into the polymer layer  1220  and the polymer layer  1220  is heated above a glass transition temperature thereof, thereby transferring the pattern to the polymer layer  1220 . 
         [0084]    After removal of the mold  1230 , a plurality of lands  1220   a  and grooves  1220   b  are formed in the polymer layer  1220 , as shown in  FIG. 12C . 
         [0085]    In  FIG. 12D , reactive ion etching removes residual portions of the polymer layer  1220  from the bottom of the grooves  1220   b,  thereby exposing surfaces of the substrate  1210 . 
         [0086]    In  FIG. 12E , a first metal layer  1240   a  and second metal layer  1240   b  are concurrently formed on the lands  1220   a  and grooves  1220   b,  respectively, using sputtering or vacuum deposition. The first metal layer  1240   a  and second metal layer  1240   b  may be silver (Ag). 
         [0087]    In  FIG. 12F , a dielectric layer  1250  is formed on the first metal layer  1240   a  and second metal layer  1240   b.    
         [0088]    In  FIG. 12G , a polarizer  1252  is disposed under the substrate  1210 . 
         [0089]    In addition, optical properties of the color filter of the embodiment are simulated by a commercial application called Gsolver.  FIG. 13  is a chart showing the transmission spectrum for the color filter shown in  FIG. 12H  with an exemplary incident light  12100 . The incident light  12100  has a wavelength between 400 and 700 nm, and an incident angle  1211 . The substrate  1210  has a thickness of 1200 micrometers. One land  1220   a  and one groove  1220   b  have a total width  1280  of 150 nm. The lands  1220   a  have a uniform width  1270  of 75 nm. The first metal layer  1240   a  and second metal layer  1240   b  have a uniform thickness  1254 , of 50, 50, or 50 nm. The first metal layer  1240   a  has a relative height  1256  exceeding that of the second metal layer  1240   b,  of 100, 140, or 165 nm. 
         [0090]    As shown in  FIG. 13 , the transmission peaks occur at 470 (blue), 550 (green), 610 nm (red), respectively. 
         [0091]    In this embodiment, each color light has a transmission approaching 90% when the width  1280  shifts to 150 nm. 
         [0092]    In other embodiments, the second metal layer may be directly formed on the residual polymer layer in the grooves without etching. 
         [0093]    Referring to  FIG. 12 , the color filter of the described embodiments comprises a substrate  1252 , a polymer layer having a plurality of lands  1220   a  and grooves  1220   b,  a first metal layer  1240   a  disposed on the lands  1220   a,  a second metal layer  1240   b  disposed on the grooves 1220 b  or a polarizer  1252 . 
         [0094]    In  FIG. 14A , a substrate  1410 , such as a glass substrate, with a polymer layer  1420  formed thereon is provided. The polymer layer  1420  may be mr-L6000.3XP manufactured by micro resist technology Inc. 
         [0095]    In  FIGS. 14A to 14B , a mold  1430  having a pattern of microstructure is pressed into the polymer layer  1420  and the polymer layer  1420  is exposed under UV light, thereby transferring the pattern to the polymer layer  1420 . 
         [0096]    After removal of the mold  1430 , a plurality of lands  1420   a  and grooves  1420   b  are formed in the polymer layer  1420 , as shown in  FIG. 14C . 
         [0097]    In  FIG. 14D , reactive ion etching removes residual portions of the polymer layer  1420  from the bottom of the grooves  1420   b,  thereby exposing surfaces of the substrate  1410 . 
         [0098]    In  FIG. 14E , a first metal layer  1440   a  and second metal layer  1440   b  are concurrently formed on the lands  1420   a  and grooves  1420   b,  respectively, using sputtering or vacuum deposition. 
         [0099]    In  FIG. 14F , a dielectric layer  1450  is formed on the first metal layer  1440   a  and second metal layer  1440   b.    
         [0100]    In  FIG. 14G , a polarizer  1452  is disposed under the substrate  1410 . 
         [0101]    In other embodiments, the second metal layer  1440   b  may be directly formed on the residual polymer layer in the grooves without etching. 
         [0102]    While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation to encompass all such modifications and similar arrangements.