Abstract:
An apparatus for demagnetizing a shadow mask includes a shadow mask stocker, a cassette in the shadow mask stocker, wherein at least one shadow mask is disposed in the cassette, and a demagnetizing means that generates a magnetic field by an alternating current (AC), thereby removing magnetism of the at least one shadow mask.

Description:
[0001]    This application claims the benefit of Korean Patent Application No. 10-2006-0056363, filed in Korea on Jun. 22, 2006, which is hereby incorporated by reference for all purposes as if fully set forth herein. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to an apparatus including a shadow mask, and more particularly, to an apparatus and a method for demagnetizing the shadow mask. 
       BACKGROUND 
       [0003]    In organic electroluminescent display devices or semiconductor devices, a thin film pattern may be formed on a substrate by using a shadow mask having desired patterns. More particularly, the shadow mask and the substrate are disposed over a source such that the shadow mask is interposed between the substrate and the source. Then, the source is evaporated and deposited on the substrate through the shadow mask. 
         [0004]    In general, a shadow mask is attached to a substrate holder with a substrate in a chamber. The shadow mask and the substrate may be fixed to the substrate holder by a mechanical fixing method or a magnetic fixing method. In the mechanical fixing method, sides of the substrate holder, the shadow mask and the substrate may be mechanically fixed using pins or clips. In the magnetic fixing method, the shadow mask is formed of a magnetic substance, and the substrate and the shadow mask may be magnetically fixed to the substrate holder by permanent magnets or electromagnets. 
         [0005]    In the magnetic fixing method, the shadow mask may be magnetized, and adjacent patterns of the shadow mask are contacted to each other due to the magnetization, causing undesirable patterns on the substrate. 
         [0006]      FIGS. 1 and 2  are views illustrating an apparatus for forming a thin film using a magnetic shadow mask according to the related art. 
         [0007]    As shown in  FIG. 1 , a shadow mask  102  is disposed over a mask holder  103  in a process chamber  101 . A substrate  105  is disposed over a substrate holder  104 , which is set up over shadow mask  102  in the process chamber  101 . 
         [0008]    The shadow mask  102  is formed of an invar, which is an alloy of ferromagnetic iron and nickel and has a relatively low coefficient of thermal expansion. The shadow mask  102  is perforated corresponding to patterns. 
         [0009]    Two cross patterns (not shown) are formed on each of the substrate  105  and the shadow mask  102 . While the cross patterns are monitored through charge-coupled device (CCD) cameras  106 , the substrate  105  moves in an x, y, z or θ direction according to images from the CCD cameras  106 . Therefore, the substrate  105  and the shadow mask  102  are aligned with each other such that the cross patterns of the substrate  105  overlap those of the shadow mask  102 . Like this, to align the substrate  105  and the shadow mask  102 , two CCD cameras  106  and two cross patterns for each of the substrate  105  and the shadow mask  102  are required. 
         [0010]    As shown in  FIG. 2 , when the substrate  105  and the shadow mask  102  are exactly aligned, a chuck  107  goes down and fixes the substrate  105 . A magnet  108  is disposed at a bottom of the chuck  107  and prevents the shadow mask  102  from hanging down. Accordingly, the shadow mask  102  including the ferromagnetic materials is easily fixed by the magnet  108  of the chuck  107 . Then, a source (not shown) is evaporated and is deposited on the substrate  105  through the shadow mask  102  to form thin film patterns. 
         [0011]    By the way, the shadow mask  102  may be magnetized depending on a magnetic field strength of the magnet  108 , causing problems. 
         [0012]    That is, the substrate  105  and the shadow mask  102  are fixed by the magnet  108  of the chuck  107 , which is ferromagnetic, and then the thin film patterns are formed on the substrate  105 . At this time, the shadow mask  102  may be magnetized. After that, the magnet  108  of the chuck  107  moves upward. Then, the shadow mask  102  may be demagnetized, and the magnetism of the shadow mask  102  may be removed. 
         [0013]    However, the shadow mask  102  is still magnetized. 
         [0014]      FIG. 3  shows a magnetized shadow mask of the related art. In  FIG. 3 , the shadow mask  102  may be a grill type. When the shadow mask  102  is fixed with the substrate  102  by the magnet  108  of  FIG. 2 , the shadow mask  102  may be magnetized. After forming the thin film patterns and removing the magnet  108 , the shadow mask  102  is still magnetized, and thus adjacent grill patterns of the shadow mask  102  may be contacted to each other. Therefore, thin film patterns may be improperly formed due to the contacted grill patterns of the shadow mask  102  in a subsequent process. Defects may be caused in a display device. 
       SUMMARY 
       [0015]    Accordingly, the present embodiments are directed to a liquid crystal display device that may substantially obviate one or more problems due to limitations and disadvantages of the related art. Additional features and advantages of the embodiments will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the embodiments. The advantages of the embodiments will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
         [0016]    In a first aspect, an apparatus for demagnetizing a shadow mask includes a shadow mask stocker, a cassette in the shadow mask stocker, wherein at least one shadow mask is disposed in the cassette, and a demagnetizing means generating a magnetic field by an alternating current (AC), thereby removing magnetism of the at least one shadow mask. 
         [0017]    In a second aspect, a method of demagnetizing a shadow mask includes disposing at least one shadow mask in a shadow mask stocker having a demagnetizing means therein, applying an alternating current (AC) to the demagnetizing means, thereby generating a magnetic field, and removing magnetism of the at least one shadow mask by the magnetic field. 
         [0018]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the disclosure as claimed. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The accompanying drawings, which are included to provide a further understanding of the embodiments and are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the description serve to explain the principles of the disclosure. In the drawings: 
           [0020]      FIGS. 1 and 2  are views illustrating an apparatus for forming a thin film using a magnetic shadow mask according to the related art; 
           [0021]      FIG. 3  shows a magnetized shadow mask of the related art; 
           [0022]      FIG. 4  is a graph showing a principle of demagnetizing a shadow mask; 
           [0023]      FIG. 5  is a view illustrating a principle of a solenoid used for a demagnetizing apparatus; 
           [0024]      FIG. 6  is a view schematically illustrating a demagnetizing apparatus using a solenoid according to a first embodiment; 
           [0025]      FIG. 7  is a view illustrating a principle of a Helmholtz coil used for a demagnetizing apparatus; and 
           [0026]      FIG. 8  is a view schematically illustrating a demagnetizing apparatus using a Helmholtz coil according to a second embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    Reference will now be made in detail to the embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. 
         [0028]      FIG. 4  is a graph showing a principle of demagnetizing a shadow mask.  FIG. 4  illustrates magnetic flux density B of the shadow mask as function of magnetic field strength H depending on magnetic fields applied to the shadow mask. 
         [0029]    In  FIG. 4 , the shadow mask has magnetic hysteresis properties depending on the applied magnetic fields. By applying magnetization currents of alternating current (AC) to the shadow mask, the magnetization of the shadow mask is gradually decreased until the magnetism of the shadow mask becomes zero. 
         [0030]    More particularly, the shadow mask  102  is magnetized due to the magnetic field of the magnet  108  such that spins of electrons are aligned along a certain direction. If electric fields of alternating current (AC) are applied to the shadow mask  102  in various ways, directions of the spins of the electrons alternately change according as a polarity of periodic AC varies. At this time, if the AC decreases, a changing extent of the spins of the electrons is also lowered, and finally, the magnetization of the shadow mask  102  becomes zero. 
         [0031]      FIG. 5  is a view illustrating a principle of a solenoid used for a demagnetizing apparatus, and  FIG. 6  is a view schematically illustrating a demagnetizing apparatus using a solenoid according to a first embodiment. 
         [0032]    In  FIG. 5 , a coil  112  is wrapped around a magnetic substance  113 , and AC from an AC power source  115  is applied to the coil  112 . 
         [0033]    In  FIG. 6 , a solenoid is set up in a shadow mask stocker  110 . A plurality of shadow masks  102  are disposed in a cassette  111 , and a coil  112  is tubularly installed around the shadow masks  102 , wherein the shadow masks  102  function as a magnetic substance. An AC power source  115  is connected to the coil  112 . 
         [0034]    If gradually decreasing AC from the AC power source  115  is applied to the coil  112 , the shadow masks  102  are demagnetized. The coil  112 , desirably, may be disposed at a side of a gate for carrying the shadow masks  102  in and out so that the shadow masks  102  can be carried in and out without hindrance. 
         [0035]      FIG. 7  is a view illustrating a principle of a Helmholtz coil used for a demagnetizing apparatus, and  FIG. 8  is a view schematically illustrating a demagnetizing apparatus using a Helmholtz coil according to a second embodiment. 
         [0036]    In  FIG. 7 , two parallel ring-shaped coils  212  are wound around a non-magnetized coil former (not shown) such that a radius “r” of the coils  212  is equal to a distance between the coils  212 , and thus an magnetic field is uniformly induced in a central portion. 
         [0037]    When a current “I” flows through each coil  212  in the same direction, at a point which is at “x” distant from a center of one of the coils  212 , a magnetic field is expressed as follows: 
         [0000]    
       
         
           
             
               H 
               = 
               
                 
                   NI 
                   
                     2 
                      
                     r 
                   
                 
                 [ 
                 
                   
                     
                       ( 
                       
                         1 
                         + 
                         
                           
                             x 
                             2 
                           
                           
                             r 
                             2 
                           
                         
                       
                       ) 
                     
                     
                       - 
                       
                         3 
                         2 
                       
                     
                   
                   + 
                   
                     
                       ( 
                       
                         1 
                         + 
                         
                           
                             ( 
                             
                               
                                 r 
                                 - 
                                 x 
                               
                               r 
                             
                             ) 
                           
                           2 
                         
                       
                       ) 
                     
                     
                       - 
                       
                         3 
                         2 
                       
                     
                   
                 
                 ] 
               
             
             , 
           
         
       
     
         [0038]    wherein “N” is the number of wire loops in one coil, and “r” is a radius of the coil. 
         [0039]    In the same number of wire loops and the same current, a magnetic field induced by the Helmholtz coil is relatively weak but generally uniform in a wide range as compared to that by the solenoid. Therefore, the Helmholtz coil is useful for the case of generating a magnetic field that is uniform in a wide range. 
         [0040]    In  FIG. 8 , a Helmholtz coil is set up in a shadow mask stocker  110 . Two parallel ring-shaped coils  212  are disposed at opposite sides of a cassette  111 , wherein the coils  212  are separated with a distance equal to a radius of the coils  212 . An AC power source  115  is connected to the coils  212 . 
         [0041]    If gradually decreasing AC from the AC power source  115  is applied to the coils  212 , the shadow masks  102  disposed between the coils  212  are demagnetized. The cassette  111 , which the coils  212  are set up to, may be formed of a non-magnetized material. 
         [0042]    A method of demagnetizing the shadow mask will be described hereinafter in more detail with reference to accompanying drawings. 
         [0043]    First, referring to  FIGS. 1 and 2 , the shadow mask  102  and the substrate  105  are disposed in the chamber  101 , and the shadow mask  102  and the substrate  105  are aligned with each other such that the cross patterns of the substrate  105  overlap those of the shadow mask  102 . The shadow mask  102  and the substrate  105  are fixed by the chuck  107 , the bottom of which the magnet  108  is combined with. Then, a thin film is formed on the substrate  105  from the patterns of the shadow mask  102  by an evaporation method or one of other deposition methods, and the chuck  107  is separated from the shadow mask  102  and the substrate  105 . The shadow mask  102  is transferred to the shadow mask stocker  110 . 
         [0044]    At this time, the shadow mask  102  is magnetized by the magnet  108  at the bottom of the chuck  107 . Referring to  FIGS. 6 and 8 , decreasing AC is applied to a demagnetizing means, such as the coil  112  of  FIG. 6  or the coils  212  of  FIG. 8 , and the shadow mask  102  is demagnetized. 
         [0045]    After that, even though the shadow mask  102  is used in the next process, there is no pattern problem because the shadow mask  102  is completely demagnetized and the patterns of the shadow mask  102  are not connected to each other. 
         [0046]    In the present invention, a demagnetizing means is set up to a shadow mask stocker, and the shadow mask is demagnetized by the demagnetizing means. Therefore, the patterns of the shadow mask may be prevented from being connected due to the magnetization of the shadow mask. This may decrease the number of defective products and increase production yields. 
         [0047]    It will be apparent to those skilled in the art that various modifications and variations can be made in the liquid crystal display device of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.