Patent Publication Number: US-6986983-B2

Title: Method for forming a reflection-type light diffuser

Description:
BACKGROUND OF INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for forming a reflection-type light diffuser, and more particularly, to a method for forming a reflection-type light diffuser applied to a reflective liquid crystal display (LCD). 
     2. Description of the Prior Art 
     Generally, there are two basic types of LCDs according to image display modes: a light transmissive type and a light reflective type. The light transmissive LCD comprises a backlight disposed on a rear side of a liquid crystal cell for emitting light. The light radiated from the backlight selectively passes through the liquid crystal cell, thereby realizing desired images. The light reflective LCD comprises a front light source and a reflective plate disposed on a rear side of the LCD so as to reflect incident light generated from the front light source toward the front side of the LCD, thereby realizing desired images. The users can choose the light transmissive LCD or the light reflective LCD of their own accord. 
     Because the prior art reflective plate of the light reflective LCD reflects the incident light towards a fixed point of view, the LCD has a narrow field of vision that restricts users to viewing displayed images on the LCD to angles around a specific angular magnitude (i.e. a visible angle). Therefore, for the purpose of increasing the visible angle of the light reflective LCD, a plurality of bump structures are formed on the reflective plate to rough the surface of the reflective plate and increase scattering angles of the reflected lights and thus broaden the viewable angle of the light reflective LCD. 
     Please refer to  FIG. 1A  to  FIG. 1D  of schematic diagrams illustrating a prior art method for forming a reflection-type light diffuser  28  on a glass substrate  10 . As shown in  FIG. 1A , a spin-coating process is performed to form a resin material layer  12  on the glass substrate  10 , and the resin material layer  12  is pre-baked for about 30 minutes at about 300° C. The glass substrate  10  has a thickness of about 1.1 centimeters (cm), and the resin material layer  12  has a thickness of about 1.5 micrometers (μm). Then as shown in  FIG. 1B , an exposing process is performed by using a photo mask  14  and a light source  20 . The photo mask  14  has a plurality of light-shielding regions  16  and a plurality of light-transmitting regions  18 , so that a photoresist pattern  22  is formed in the resin material layer  12  after a subsequent developing process, as shown in  FIG. 1C . As shown in  FIG. 1D , a soft baking process is performed to soften the photoresist pattern  22  to form a continuous photoresist pattern  24 . A metal layer  26  is formed on the glass substrate  10  and the reflection-type light diffuser  28  is completed. The metal layer  26  comprises aluminum (Al), nickel (Ni), chromium (Cr), or silver (Ag) metal, and the metal layer  26  has a thickness of between 0.01 to 1.0 μm. The photoresist pattern  24  comprises a plurality of bump structures  24 . 
     Because the reflection-type light diffuser  28  has a plurality of bump structures  24 , the surface of the reflection-type light diffuser  28  is rough and uneven. When incident light  30  enters the reflection-type light diffuser  28 , the incident light  30  generates a plurality of scattering lights  32  by reflecting from the metal layer  26  and the bump structures  24 . However, the bump structures  24  are disposed on the reflection-type light diffuser  28  randomly, so that the scattering directions of the scattering lights are too wide and thus result in weakening the scattering light  32  intensity. In addition, the scattering lights  32  also interfere with each other. Therefore, another reflection-type light diffuser is disclosed to solve the above-mentioned problems. 
     Please refer to  FIG. 2A  to  FIG. 2F  of schematic diagrams illustrating a prior art method for forming a reflection-type light diffuser  52  on a glass substrate  40 . As shown in  FIG. 2A , a resin material layer  42  is spin-coated on the glass substrate  40 , and the glass substrate  40  is pre-baked. As shown in  FIG. 2B , an exposing and developing process is performed by using a photo mask  44  to form a photoresist pattern  46  in the resin material layer  42 . The photoresist pattern  46  comprises a plurality of straight protrusions, as shown in  FIG. 2C . Then as shown in  FIG. 2D , the glass substrate  40  is turned over 90 degrees and thus tilted toward a perpendicular direction. A thermal treatment process is performed to soften the photoresist pattern  46 . Since the photoresist pattern  46  is made of heated plastic material, the photoresist pattern  46  can be heated and softened to form a photoresist pattern  48  using gravity. The photoresist pattern  48  includes asymmetrical silt structures as shown in  FIG. 2E . Finally, as shown in  FIG. 2F , the glass substrate  40  is put back to its original horizontal position and then cooled down. A metal layer  50  is formed on the glass substrate  40  and the reflection-type light diffuser  52  is completed. 
     When incident light  54  enters the reflection-type light diffuser  52 , the incident light  54  generates a plurality of scattering lights  56  by reflecting from the metal layer  50  and the straight protrusions  48 . However, the reflection-type light diffuser  52  with the straight protrusions  48  still has a problem of the light directionality. Therefore, the U.S. Pat. No. 6,163,405 discloses a reflection-type light diffuser to solve the problems of light scattering and light direction. Please refer to  FIG. 3  of a schematic diagram illustrating a prior art reflection-type light diffuser  68 . As shown in  FIG. 3 , a photoresist pattern  62  and a metal layer (not shown in  FIG. 3 ) are formed on a glass substrate  60 , and the photoresist pattern  62  comprises a plurality of parallel slant structures  64  and a plurality of knob structures  66  disposed on the slant structures  64 . A multi-exposure shift process is utilized to form the slant structures  64  by using a photo mask (not shown in the  FIG. 3 ). The photo mask is moved at a fixed distance many times and the exposure processes with different exposure powers are performed to form the slant structures  64  in the multi-exposure shift process. And then another photo mask (not shown in the  FIG. 3 ) is utilized to form the knob structures  66  on the slant structures  64 . Although the reflection-type light diffuser  68  with the knob on slant structures improves the above-mentioned problems, the structures are fabricated by using the exposure processes many times and the two different photo masks to form the knob on slant structures, resulting in complicating the process and increasing costs. 
     SUMMARY OF INVENTION 
     It is therefore a primary objective of the claimed invention to provide a method for fabricating a reflection-type light diffuser to solve the problems of light scattering and the light directionality of the prior art light diffuser. 
     It is another objective of the claimed invention to provide a simplified method for fabricating a reflection-type light diffuser. 
     According to the claimed invention, the reflection-type light diffuser is formed on a glass substrate, the glass substrate comprises a pixel matrix array disposed on the substrate, the pixel matrix array comprises a plurality of adjacent pixel regions, and each of the pixel regions has a pair of side edges which are parallel and opposite. A photoresist layer is formed on the substrate, and an exposing and developing process is performed by using a photo mask to form a photoresist pattern in the photoresist layer. The photoresist pattern comprises a plurality of wave-shaped straight protrusions positioned on the side edges of each of the pixel regions and a plurality of bump structures positioned on each of the pixel regions. A reflective metal layer is formed on the photoresist pattern. 
     It is an advantage that the claimed invention uses the exposing and developing process for only one time to form the wave-shaped straight protrusions and the bump structures simultaneously so as to simplify the process and reduce costs. In addition, the reflection-type light diffuser with the wave-shaped straight protrusions and the bump structures improves the problems of light scattering and the light directionality. 
     These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  to  FIG. 1D  are schematic diagrams of a prior art method for forming a reflection-type light diffuser. 
         FIG. 2A  to  FIG. 2F  are schematic diagrams of a prior art method for forming a reflection-type light diffuser. 
         FIG. 3  is a schematic diagram of a prior art reflection-type light diffuser. 
         FIG. 4  to  FIG. 6  are schematic diagrams of a reflection-type light diffuser and related method according to the first embodiment of the present invention. 
         FIG. 4A  and  FIG. 4B  are top views of photo masks utilized in the first embodiment of the present invention. 
         FIG. 7  is a top view of a photo mask utilized in the second embodiment of the present invention. 
         FIG. 8  is a schematic diagram of a reflection-type light diffuser according to the second embodiment of the present invention. 
         FIG. 9  is a cross-sectional view of the reflection-type light diffuser shown in  FIG. 8 . 
         FIG. 10  is a cross-sectional view of the reflection-type light diffuser of the first embodiment of the present invention applied to a reflective LCD. 
         FIG. 11  is a top view of the reflection-type light diffuser of the first embodiment of the present invention applied to the reflective LCD. 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIG. 4  to  FIG. 6  of schematic diagrams illustrating a reflection-type light diffuser  76  formed on a glass substrate  60  and related method according to the first embodiment of the present invention.  FIG. 4A  and  FIG. 4B  are top views illustrating photo masks  64 ,  78  utilized in the first embodiment of the present invention.  FIG. 5  is a cross-sectional view illustrating the reflection-type light diffuser  78  along a tangent line BB shown in  FIG. 6 .  FIG. 6  is a schematic diagram illustrating the reflection-type light diffuser according to the first embodiment of the present invention. As shown in  FIG. 4 , a positive photoresist layer  62  is spin-coated on the glass substrate  60 , and the photoresist layer  62  is pre-baked for about 30 minutes at approximately 80 to 90° C. The photoresist layer  62  has a thickness of between 4.8 to 5.5 μm. Then, a photo mask  64  (along the tangent line AA′ as shown in  FIG. 4A ) is utilized to perform an exposing process, and a photoresist pattern (not shown in  FIG. 4 ) is formed in the photoresist layer  62 . The photo mask  64  includes a plurality of light shielding regions  66  and a plurality of light transmitting regions  68  according to demands of the reflection-type light diffuser process. 
     As shown in  FIG. 5 , a developing process is performed to remove the photoresist layer  62  not exposed by the light shielding regions  66  of the photo mask  64 . Further, a baking process with a temperature of approximately 130° C. and a follow-up baking process with a temperature of approximately 220° C. are performed in sequence. The photoresist pattern includes a plurality of parallel straight protrusions  70  and a plurality of bump structures  72  positioned between adjacent straight protrusions  70 . The straight protrusions  70  has a pair of opposite side edges, and the side edges are straight lines. After that, a reflective metal layer  74  is formed on the photoresist pattern, and the reflection-type light diffuser  76  is completed. However, the present invention is not limited in this. A photo mask  78  shown in  FIG. 4B  can be used in the exposing and developing pocess to form another photoresist pattern. The photoresist pattern also includes a plurality of straight protrusions  70  and a plurality of bump structures, but the side edges of the straight protrusions  70  are wave-shaped as shown in  FIG. 6 . The photo mask  78  includes a plurality of light shielding regions  77 A,  77 B and a plurality of light transmitting regions  79 . The light shielding regions  77 A of the photo mask  78  correspond to the wave-shaped parallel straight protrusions  70  of the photoresist pattern and the light shielding regions  77 B corresponds to the bump structures  72  of the photoresist pattern. 
     Please refer to  FIG. 7  to  FIG. 9 .  FIG. 7  is a top view illustrating a photo mask  80  according to the second embodiment of the present invention.  FIG. 8  is a schematic diagram illustrating a reflection-type light diffuser  90  according to the second embodiment of the present invention.  FIG. 9  is a cross-sectional view illustrating the reflection-type light diffuser  90  along a tangent line CC′ shown in  FIG. 8 . As shown in  FIG. 7 , the photo mask  80  includes a plurality of light shielding regions  82  and a plurality of light transmitting regions  84 , and the light shielding regions  82  include a plurality of first light shielding regions  86  and a plurality of,second light shielding regions  88 . Utilizing the photo mask  80  as the photo mask  64  shown in  FIG. 4  to perform an exposing and developing process, then a photoresist pattern including a plurality of parallel wave-shaped straight protrusions  92  and a plurality of bump structures  94  disposed between adjacent straight protrusions  92  is formed on the glass substrate as shown in  FIG. 8 . The first light shielding regions  86  correspond to the parallel wave-shaped straight protrusions  92  of the photoresist pattern and the second light shielding regions  88  correspond to the bump structures  94  of the photoresist pattern. 
     In addition, the reflection-type light diffuser of the present invention can be applied to a reflective liquid crystal display (LCD). Please refer to  FIG. 10  and  FIG. 11 .  FIG. 10  is a cross-sectional view illustrating the reflection-type light diffuser  76  applied to a reflective LCD  128 .  FIG. 11  is a top view illustrating the reflection-type light diffuser  76  applied to the reflective LCD  128 . As shown in  FIG. 10 , the reflective LCD  128  is formed on a glass substrate  100 . The glass substrate  100  includes a pixel matrix array  102  disposed on the glass substrate  100 . The pixel matrix array  102  includes a plurality of adjacent pixel regions  104 , and each of the pixel regions  104  has a pair of side edges which are parallel and opposite as shown in  FIG. 11 . First, a thin film transistor (TFT) structure  106  is formed at a corner of each of the pixel regions  104  on the glass substrate  100 . The TFT structure  106  includes a gate conductive layer, an insulating layer, a semiconductor layer, a source electrode and a drain electrode. Then, the reflection-type light diffuser  76  or the reflection-type light diffuser  90  is formed on the glass substrate  100 . In the preferred embodiment of the present invention, the reflection-type light diffuser  76  is utilized as an example. For the purpose of connecting the reflective metal layer  74  of the reflection-type light diffuser  76  and the drain electrode of the TFT  106 , an opening is formed before depositing the reflective metal layer  74 . Then, the reflective metal layer  74  is deposited on the glass substrate  100  and is filled with the opening to form a contact hole  110 , and an orientation film  112  is formed on the glass substrate  100 . 
     Further, a filter array  116  is formed on another glass substrate  114 . The filter array  116  includes a R/G/B CFA  118  and a black filter array  120 . Further, a transparent electrode, such as ITO  122 , and an orientation film  124 , are formed on the glass substrate  114 , respectively. After that, the glass substrate  100  and the glass substrate  114  are positioned face to face so that the R/G/B CFA  116  corresponds to the reflective metal layer  74 , and the black filter array  120  corresponds to the TFT  106 . Then, a liquid crystal (LC) is injected between the glass substrate  100  and the glass substrate  114 , and the reflective LCD  128  is completed. 
     When incident light (not shown in  FIG. 10  and  FIG. 11 ) enters the reflective LCD  128 , the incident light passes through the glass substrate  14 , the CFA  116 , the transparent conductive layer  122 , the orientation film  124 , the LC  126 , the orientation film  112 , and then reaches the surface of the reflective metal layer  74  of the reflection-type light diffuser  76 . Because the surface of the reflection-type light diffuser  76  has the plurality of wave-shaped straight protrusions  70  and the plurality of bumps structures  72 , the incident light does not reflect toward a fixed direction, but scatters toward different directions. 
     In summary, the reflection-type light diffuser with the photoresist pattern includes the plurality of wave-shaped straight protrusions and the plurality of bumps structures on the glass substrate. Since the curvatures of the surface and the side edges of the wave-shaped straight protrusions and the bumps structures are varied, the incident light reflects and scatters toward various directions. Because the curvatures of the wave-shaped straight protrusions and the bumps structures are controlled by the exposing time, the exposing time relates to the thickness of the photoresist pattern. Therefore, the curvatures of photoresist pattern can be adjusted to a desired scattering direction according to the process demand. In addition, the present invention only uses the exposing and developing process once to form the wave-shaped straight protrusions and the bump structures simultaneously so as to simplify the process and reduce costs. 
     In contrast to the prior art technology, the present invention utilizes the exposing and developing process once to form the reflection-type light diffuser with the wave-shaped straight protrusions and the bump structures, which simplifies manufacturing processes and reduces costs. Since the wave-shaped straight protrusions and the bump structures positioned on the reflection-type light diffuser improve the problems of light directionality and the light scattering of the prior art reflective light diffuser, this results in no reduction of scattering light intensity and no color dissipation. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.