Patent Publication Number: US-2006019181-A1

Title: [method of manufacturing color filter array and thin film]

Description:
BACKGROUND OF INVENTION  
      1. Field of the Invention  
      The present invention relates to a method of manufacturing a thin film. More particularly, the present invention relates to a method of manufacturing a color filter film on a substrate (color filter array).  
      2. Description of the Related Art  
      With the increase in the capability of computers and the progress in networking and multimedia techniques, image data are now mostly transmitted in a digital rather than analogue format. To fit our modern lifestyle, video or imaging equipment is becoming lighter and slimmer. Although the conventional cathode ray tube (CRT) has many advantages, the design of the electron gun renders it heavy and bulky. Moreover, there is always some danger of hurting viewer”s eyes due to the emission of a little radiation. With big leaps in the techniques of manufacturing semiconductor devices and opto-electronic devices, flat panel displays such as liquid crystal displays (LCD), organic light-emitting displays (OLED) and plasma display panel (PDP) have gradually become mainstream display products.  
      In general, liquid display devices can be divided into direct viewing displays such as liquid crystal display monitors and digital liquid crystal televisions and indirect viewing displays applied in liquid crystal projectors and back projection televisions. In recent years, liquid crystal displays are aiming towards the provision of full coloration, a large screen, a high resolution and a low production cost. However, direct viewing displays have many restrictions with regards to screen size and production cost. Thus, a reflective-micro display panel with a high resolution such as a liquid crystal on silicon (LCOS) display panel together with an optical engine are often used to produce a liquid crystal projector and back projection television having a large screen.  
      LCOS panel is a reflective type liquid crystal panel set up on a silicon substrate. In a LCOS panel, metal-oxide-semiconductor (MOS) transistors are formed on the silicon substrate for controlling the liquid crystal layer above various pixel electrodes. In addition, the pixel electrodes of the LCOS panel are fabricated using a metallic material so that incident light passing through the liquid crystal layer from an external light source can be reflected back to emerge from the color filter array for display. Because the LCOS panel is set up on a silicon substrate, the LCOS panel occupies a volume smaller than a conventional direct viewing display panel and yet has a higher resolution. In other words, the LCOS panel is particularly suitable for producing projection displays with a large screen.  
      Nowadays, the color filter array of a LCOS panel is still fabricated using a conventional process. However, as the resolution of the LCOS panel continues to increase while the panel is miniaturized, the conventional method of fabricating the color filter array can no longer meet the precision required.  
       FIGS. 1A through 1D  are schematic cross-sectional views showing the steps for fabricating a conventional color filter array. As shown in  FIG. 1A , a filter material layer  102   a  is formed over a glass substrate  100 . As shown in  FIG. 1B , a patterned photoresist layer  110  is formed over the filter material layer  102   a . The photoresist layer  110  exposes a portion of the filter material layer  102   a . Thereafter, as shown in  FIG. 1C , the exposed filter material layer  102   a  is removed. As shown in  FIG. 1D , after removing the photoresist layer  110 , the exposed filter material layer  102   a  forms a plurality of color filter films  102 . Similarly, other color filter films are formed over the glass substrate  100 .  
      It should be noted that the filter material layer in the aforementioned process of forming the color filter array is removed by an etching process. However, the process of removing the filter material layer often leads to overetching. Furthermore, the solution for etching the filter material layer is not an anisotropic etching solution and hence a color filter film with vertical sidewalls is hard to produce. Consequently, as the demands for display panels having a higher resolution and a smaller size continue to increase, light leak at the edge of the color filter film due to scattering will intensify. Ultimately, the display quality of micro-displays will also be affected.  
     SUMMARY OF INVENTION  
      Accordingly, at least one objective of the present invention is to provide a method of manufacturing color filter films on a substrate such that the color filter films have vertical sidewalls for producing a better display quality.  
      At least a second objective of the present invention is to provide a method of manufacturing thin films such that two photoresist processes are used to produce vertical sidewalls at the edge of the films and the photoresist layers in the photoresist processes are used to protect the films.  
      To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method of manufacturing a color filter array. The manufacturing method is as follows. Step (a), form a patterned first photoresist layer over a substrate. The patterned first photoresist layer has a plurality of openings that exposes a portion of the substrate. Step (b), form a filter material layer on the exposed area of the substrate. Step (c), form a second photoresist layer on the filter material layer. Step (d), remove the first and the second photoresist layer such that the filter material layer forms a plurality of first filter films. Step (e), repeat step (a) to (c) at least once and remove the first and the second photoresist layer to form a plurality of second filter films in areas except the first color filter films.  
      In one preferred embodiment of the present invention, the filter material layer also forms over the first photoresist layer. Furthermore, after the step (c), further includes a step (c1) of removing the filter material layer above the first photoresist layer. In addition, the filter material layer has a thickness smaller than or equal to the first photoresist layer.  
      The present invention also provides a method of manufacturing thin films. The manufacturing method is as follows. Step (a), form a patterned first photoresist layer over a substrate. The patterned first photoresist layer has a plurality of openings that exposes a portion of the substrate. Step (b), form a material layer on the exposed area of the substrate. Step (c), form a second photoresist layer on the material layer. Step (d), remove the first and the second photoresist layer such that the material layer forms a plurality of thin films.  
      In one preferred embodiment of the present invention, the material layer also forms over the first photoresist layer. Furthermore, after the step (c), further includes a step (c1) of removing the material layer above the first photoresist layer. In addition, the material layer has a thickness smaller than or equal to the first photoresist layer.  
      In brief, the method of fabricating the color filter array and thin films according to the present invention includes forming a patterned first photoresist layer over a substrate and then forming thin films inside the openings in the first photoresist layer. Therefore, shaped by the first photoresist layer, the thin films have vertical sidewalls. Furthermore, the second photoresist layer covers the thin films inside the opening and prevents the thin films from any attack by etching solution when the material layer on the first photoresist layer is removed. Thus, the present invention not only provides a thin film with vertical sidewalls, but also provides a method of fabricating an ideal color filter film on a substrate to improve the display quality of a display panel.  
      It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
      The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.  
       FIGS. 1A through 1D  are schematic cross-sectional views showing the steps for fabricating a conventional color filter array.  
       FIGS. 2A through 21  are schematic cross-sectional views showing the steps for fabricating a color filter array according to one preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION  
      Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.  
      The present invention not only provides a method of fabricating a color filter array, but also provides a method of fabricating a thin film. However, since the method of fabricating a thin film is subsumed under the fabrication of the color filter array, only the process of fabricating the color filter array is described in the following.  
       FIGS. 2A through 21  are schematic cross-sectional views showing the steps for fabricating a color filter array according to one preferred embodiment of the present invention. As shown in  FIG. 2A , a patterned first photoresist layer  210  is formed over a substrate  200 . The first photoresist layer  210  has a plurality of openings  210   a  that exposes a portion of the substrate  200  and the substrate  200  is a glass plate, for example. The first photoresist layer  210  is formed, for example, by coating a positive photoresist or a negative photoresist layer over the substrate  200  and performing a photolithographic process to define the openings  210   a.    
      As shown in  FIG. 2B , a first filter material layer  202   a  is formed over the substrate  200 . The first filter material layer  202   a  covers the first photoresist layer  210  and the exposed substrate  200  within the openings  210   a . Due to the step height between the top surface of the first photoresist layer  210  and the top surface of the substrate  200 , the first filter material layer  202   a  within the openings  210   a  may separate from the first filter material layer  202   a  on the first photoresist layer  210 . Furthermore, through the openings  210   a  in the first photoresist layer  210 , the sidewalls of the first filter material layer  202   a  are close to vertical. It should be noted that the thickness of the first filter material layer  202   a  is smaller than or equal to the thickness of the first photoresist layer  210  in one embodiment of the present invention. As a result, the first filter material layer  202   a  within the openings  210   a  and the first filter material layer  202   a  on the first photoresist layer  210  are more sharply detached from each other.  
      As shown in  FIG. 2C , a patterned second photoresist layer  220  is formed over the substrate  200 . The second photoresist layer  220  covers the first filter material layer  202   a  inside the openings  210   a  but exposes the first filter material layer  202   a  over the photoresist layer  210 . The second photoresist layer  220  and the first photoresist layer  210  are positive photoresist or negative photoresist layer, for example. Similarly, the second photoresist layer  220  is patterned using photolithographic processes, for example.  
      As shown in  FIG. 2D , the first filter material layer  202   a  over the first photoresist layer  210  is removed. The method of removing the first filter material layer  202   a  includes, for example, performing a chemical etching process. Because the second photoresist layer  220  covers the first filter material layer  202   a  inside the openings  210   a , the first filter material layer  202   a  underneath the second photoresist layer  220  is protected from the etching solution. In other words, only the first filter material layer  202   a  over the first photoresist layer  210  is removed after the etching process.  
      As shown in  FIG. 2E , the first photoresist layer  210  and the second photoresist layer  220  are removed. The first filter material layer  202   a  originally inside the openings  210   a  and protected by the second photoresist layer  220  is exposed to form a plurality of first color filter films  202 .  
      After the completion of steps as shown in  FIGS. 2A through 2E , a plurality of first color filter films is formed on the substrate. To form a complete color filter array (having three colors red, green and blue), the aforementioned procedure must be repeated at least twice. In other words, color filter films of other colors must be formed on the substrate except the regions occupied by the first color filter films. In the following, the steps for fabricating other color filter films are described. Since the structure and manufacturing method of the other thin films is similar to the ones already described in  FIGS. 2A through 2E , detailed description is omitted.  
      As shown in  FIG. 2F , a patterned third photoresist layer  230  is formed over the substrate  200 . The third photoresist layer  230  covers the first color filter films  202 . Furthermore, the third photoresist layer  230  has a plurality of openings  230   a  that exposes a portion of the substrate  200  except the first color filter films  202  occupied areas. Thereafter, a second filter material layer  204   a  is formed over the substrate  200  to cover the third photoresist layer  230  and the exposed substrate  200  within the openings  230   a . A patterned fourth photoresist layer  240  is formed over the second filter material layer  204   a  inside the openings.  230   a.    
      As shown in  FIG. 2G , the second filter material layer  204   a  over the third photoresist layer  230  is removed. Thereafter, the third photoresist layer  230  and the fourth photoresist layer  240  are removed to form a plurality of second color filter films  204  over the substrate  200 .  
      As shown in  FIG. 2H , a patterned fifth photoresist layer  250  is formed over the substrate  200 . The fifth photoresist layer  250  covers the first color filter films  202  and the second color filter films  204 . Furthermore, the fifth photoresist layer  250  has a plurality of openings  250   a  that exposes a portion of the substrate  200  except the occupied areas of the first color filter films  202  and the second color filter films  204 . Thereafter, a third filter material layer  206   a  is formed over the substrate  200  to cover the fifth photoresist layer  250  and the exposed substrate  200  within the openings  250   a . A patterned sixth photoresist layer  260  is formed over the third filter material layer  206   a  inside the openings  250   a.    
      As shown in  FIG. 21 , the third filter material layer  206   a  over the fifth photoresist layer  250  is removed. Thereafter, the fifth photoresist layer  250  and the sixth photoresist layer  260  are removed to form a plurality of third color filter films  206  over the substrate  200 .  
      In summary, the method of fabricating the color filter array and thin films according to the present invention includes forming a patterned photoresist layer over a substrate and then forming thin films inside the openings in the first photoresist layer. Therefore, shaped by the photoresist layer, the films can have vertical sidewalls. Furthermore, after filling the openings with filter material, another photoresist layer covers the thin films inside the opening. Hence, the thin films are prevented from any attack by etching solution in a subsequent etching process. Thus, the present invention not only provides a thin film with vertical sidewalls, but also provides a method of fabricating an ideal color filter film on a substrate to improve the display quality of a display panel.  
      It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.