Patent Publication Number: US-2010127621-A1

Title: Method for manfacturing flat panel display and panel for flat panel display

Description:
TECHNICAL FIELD 
     The present invention relates to a process for manufacturing a flat panel display in which coating of electrodes is performed by a chemical vapor deposition process. 
     BACKGROUND ART 
     The chemical vapor deposition (CVD) process is a method for forming a film from a source gas by a chemical reaction, which is widely used for industrial applications including formation of a thin film of a micro device such as a semiconductor device and coating of an object in the order of meters. 
     The CVD process has recently been used also for manufacturing a flat panel display having a large screen of one meter diagonal size or larger. Japanese Patent No. 3481142 describes a method for manufacturing an AC plasma display panel in which a dielectric layer for coating electrodes is formed by a plasma enhanced CVD process. According to the CVD process, it is possible to obtain a dielectric layer having a thin and uniform thickness. In addition, compared to a thick film process, it is possible to form the dielectric layer made of a material such as silicon dioxide or organic silicon oxide having a smaller relative dielectric constant than a low melting point glass as a common material at low temperatures. 
     If the object has a part not to be coated in the CVD process for forming a film, masking of the part is performed. Japanese unexamined patent publication No. 2003-324075, which is a related-art document about masking, discloses a masking member that is a combination of a rectangular frame and a thin band-like member. 
     [Patent Document 1] Japanese Patent No. 3481142 
     [Patent Document 2] Japanese unexamined patent publication No. 2003-324075 
     DISCLOSURE OF THE INVENTION 
     If the dielectric layer that covers electrodes is formed by the CVD process in the manufacturing process of a plasma display panel, it is difficult to make terminal parts of the electrodes be exposed without loss of mass production efficiency. 
     In order to make terminal parts of the electrodes be exposed, the dielectric layer should be removed partially after depositing the dielectric so as to cover the entire of the electrodes or masking is performed by placing a mask on the terminal parts of the electrodes before depositing the dielectric on the substrate on which the electrodes are arranged. 
     A common method for removing the dielectric layer partially is a wet etching process. However, when the wet etching process is used, the terminal parts of the electrodes are apt to disappear. In other words, there is no appropriate etchant that has selectivity for dissolving the dielectric layer formed by the CVD process and not dissolving the electrodes and that has excellent cost efficiency and safety. For example, hydrofluoric acid that can dissolve silicon dioxide does not have selectivity for copper or chromium that is a typical material of the terminal parts of electrodes. Therefore, if the dielectric layer made of silicon dioxide is etched by the hydrofluoric acid, it is necessary to perform very precise etching control for minimizing dissolution of the terminal parts of electrodes and to decrease an etching rate for this purpose. As a result, the turnaround time becomes long. 
     On the other hand, the masking method is useful from the viewpoint of the turnaround time because it does not need to make the terminal parts be exposed after forming the film. However, it has a problem that occurrence probability of a break or a continuity defect of an electrode may be increased due to the masking. 
     An object of the present invention is to enhance mass production efficiency in manufacturing a flat panel display having an insulator layer that covers electrodes and is formed by the chemical vapor deposition process. 
     A method for forming a film for achieving the object of the present invention is a method for manufacturing a flat panel display in which an insulator layer is formed by a CVD process on a substrate on which electrodes are arranged, and includes the steps of disposing a mask having a shape covering terminal parts of the electrodes so as to be close to, but be separated from and be opposed to the terminal parts, and depositing an insulator on the electrodes at a deposition rate of chemical vapor deposition that is lower at the terminal parts than at parts of the electrodes that are not covered with the mask. 
     The inventor found that a break of an electrode is caused when the mask touches the electrode. It was found that if the mask touches the electrode, the terminal part can be damaged largely or the surface of the terminal part can be damaged resulting in oxidation of the surface in a heat treatment process after the film forming process. Therefore, according to the present invention, the mask is disposed away from the terminal part by a tiny distance so as to be opposed to the same. Since there is a gap between the mask and the terminal parts, the insulator will be deposited also on the terminal parts in the CVD process unlike the case where the mask contacts the electrode. However, the deposition rate depends on a size of the gap. Since the deposition rate is lower as the size of the gap is smaller, the thickness of the insulator layer formed on the terminal parts of the electrode is sufficiently thinner than that formed on other parts in the film forming process in the state where the mask is close to the terminal parts. 
     If the thin insulator layer covering the terminal parts can be an obstacle to electric connection to the terminal parts, it is removed by a chemical or physical etching process, a sanding process or other methods prior to the electric connection. The thin insulator layer can be removed in a shorter time than the case of removing a thick insulator layer. In order to reduce the time necessary for removing the thin insulator layer, it is desirable that the thickness of the insulator layer covering the electrodes at the terminal parts be 1/10 or less of the thickness of the same at other parts. 
     If the insulator layer covering the terminal parts is very thin, i.e., if a wiring conductor can break the insulator layer and is connected electrically to the terminal part when it is pressed to contact the terminal part, it is not necessary to remove the insulator layer prior to the electric connection. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view showing an example of a cell structure of a plasma display panel. 
         FIG. 2  is a plan view showing a layout pattern of display electrodes. 
         FIG. 3  is a plan view showing regions to be masked when a dielectric layer is formed in a manufacturing process of the plasma display panel. 
         FIG. 4  is a plan view of a mask. 
         FIG. 5  is a plan view of a mask and a frame for supporting the same. 
         FIG. 6  is a schematic diagram showing a general structure of a plasma CVD device. 
         FIGS. 7(A) and 7(B)  are cross sectional views showing the masking according to the present invention. 
         FIG. 8  is a cross sectional view showing a first example of a panel structure according to the present invention. 
         FIG. 9  is a cross sectional view showing a second example of the panel structure according to the present invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, a method of the present invention for manufacturing a plasma display panel as an example will be described. 
     A typical plasma display panel has a cell structure as shown in  FIG. 1 .  FIG. 1  shows a part including six cells corresponding to three columns in two rows, in which a front plate  10  and a rear plate  20  are separated for easy understanding of the internal structure. 
     The plasma display panel  1  includes the front plate  10 , the rear plate  20  and discharge gas (not shown). The front plate  10  includes a glass substrate  11 , first row electrodes X, second row electrodes Y, a dielectric layer  17 , and a protection film  18 . Each of the row electrodes X and the row electrodes Y is a laminate of a patterned transparent conductive film  14  and a metal film  15 . The rear plate  20  includes a glass substrate  21 , column electrodes A, a dielectric layer  22 , a plurality of partitions  23 , a red (R) fluorescent material  24 , a green (G) fluorescent material  25 , and a blue (B) fluorescent material  26 . 
     As display electrodes for generating surface discharge, the row electrodes X and the row electrodes Y are arranged alternately on the inner surface of the glass substrate  11  and are covered with the dielectric layer  17  and the protection film  18 . The dielectric layer  17  is an essential element for the AC plasma display panel. The coating with the dielectric layer  17  enables surface discharge to be generated repeatedly by utilizing wall charge accumulated in the dielectric layer  17 . The protection film  18  protects the dielectric layer  17  from sputtering. 
     Note that either one of the well-known arrangement forms of the row electrodes can be adopted in the embodiment of the present invention. One of them is as shown in  FIG. 1 , in which an electrode gap between neighboring rows is larger than an electrode gap in each row (i.e., a surface discharge gap). The other arrangement has a uniform row electrode gap for all rows. 
       FIG. 2  is a plan view showing a layout pattern of the display electrodes. The row electrodes X and the row electrodes Y that constitute a display electrode group  40  extend from the screen  60  to the vicinity of the edge of the glass substrate  11 , and terminals Xt and Yt are disposed at the end of them for electric connection with a drive unit. In  FIG. 2 , the terminals Xt of the row electrodes X are disposed on the left end side of the glass substrate  11 , while the terminals Yt of the row electrodes Y are disposed on the right end side of the glass substrate  11 . An arrangement pitch of the terminals Xt is different from an arrangement pitch of the row electrodes X on the screen  60 , so the left end parts of the row electrodes X (including the terminals Xt) are patterned in shapes like curved bands. This curved part is not the laminate of the transparent conductive film  14  and the metal film  15  but is made of only the metal film  15 . In the same manner, the right end parts of the row electrodes Y (including the terminals Yt) are patterned in shapes like curved bands, and this curved part is made of only the metal film  15 . 
     The plasma display panel  1  having the structure described above is manufactured according to the procedure in which the front plate  10  and the rear plate  20  are made separately and after that they are glued to each other. In general, a mother glass plate having an area twice or more of the glass substrate  11  is used for manufacturing the front plate  10 , so that a plurality of front plates  10  are made at one time. In the same manner, a plurality of rear plates  20  are made at one time. Prior to gluing the front plate  10  and the rear plate  20  together, the mother glass plate is divided so that each of the front plates  10  is glued to each of the rear plates  20  to be one unit. 
     In the manufacturing process of the front plate  10 , the dielectric layer  17  made of a single layer is formed by the CVD process, in which the masking of the terminals Xt and Yt is performed. If the masking is not performed, the entire of the display electrode group  40  including the terminals Xt and Yt will be covered with the dielectric layer  17  of a single layer having a uniform thickness. Then, it will take a long time to make the terminals Xt and Yt be exposed by an etching process or a sanding process. Since the masking is performed, a step for removing the dielectric layer  17  partially becomes unnecessary, or it can be removed in a relatively short time even if the step is necessary. 
     If two glass substrates are obtained from one mother glass plate (two in one) as an example, in the formation of the dielectric layer, the masking should be performed on the regions S 11  and the regions S 12  as shown in  FIG. 3 . In  FIG. 3 , two display electrode groups  40  are formed in parallel on a mother glass plate  111 . The part of the mother glass plate  111  where the display electrode group  40  is arranged and the vicinity of the part correspond to the glass substrate  11  on the front side of one plasma display panel. The region S 11  corresponds to the terminal parts on the left side of each of the display electrode groups  40  while the region S 12  corresponds to the terminal parts on the right side of each of the display electrode groups  40  in  FIG. 3 . 
     The masking is performed by using two masks  71  and  72  as shown in  FIG. 4 . The masks  71  and  72  are elongated band-like plates made of an insulation material such as a ceramic or a heat-resistant glass and are disposed so as to overlap the mother glass plate  111  at the end parts. 
     A size of the masks  71  and  72  is selected in accordance with a size of a screen of the plasma display panel. For example, the glass substrate of the plasma display panel having a 42 inch diagonal screen  60  has dimensions of approximately 994 mm×585 mm. If the glass substrate is obtained in “two in one”, the area of the mother glass plate  111  should be larger than two times the screen (994 mm×1170 mm). A width of the masks  71  and  72  is approximately 20-30 mm, and a length of the same is approximately the same as the corresponding side of the mother glass plate  111 . A thickness of the same is approximately 5±2 mm. 
     When the masks  71  and  72  are used, they are supported by a rectangular frame  73  as shown in  FIG. 5 . The frame  73  is a rigid body made of an aluminum alloy having a thickness of approximately 30 mm, and it is larger and thicker than the mother glass plate  111 . Thus, the frame  73  is provided with a sufficient mechanical strength as a pressure member for preventing the mother glass plate  111  from being warped by heat. 
     The dielectric layer is formed by using the masks  71  and  72  in a plasma CVD device  300  shown in  FIG. 6 , which is a parallel plate type. The plasma CVD device  300  includes a chamber (a reaction chamber)  310  made of a metal container, a shower plate  320  for spouting source gas uniformly in a wide range, a movable base  330  for supporting an object on which a film should be formed, the masks  71  and  72  for the above-mentioned masking, and the frame  73  for supporting the masks  71  and  72 . 
     The shower plate  320  also works as an upper electrode for generating plasma, and the movable base  330  also works as a lower electrode. A heater for heating the object on which the film should be formed is embedded in the movable base  330 . 
     Inside the chamber  310 , the masks  71  and  72  are disposed between the shower plate  320  and the movable base  330 . In the illustrated state of forming the film, the mother glass plate  111  on which the display electrode groups  40  are formed is placed on the movable base  330 , so that the lower faces of the masks  71  and  72  are disposed close to the upper faces of the display electrode groups  40 . Plasma is generated in the space between the display electrode groups  40  and the shower plate  320 . A distance D between the mother glass plate  111  and the shower plate  320  is selected to be approximately 10 to 20 mm. 
     The movable base  330  in this example is a lift type that can move up and down. When the mother glass plate  111  is carried in or out, the movable base  330  moves down so as to be separate from the fixed frame  73 . The chamber  310  is provided with a mechanism for carrying the mother glass plate  111  in and out, which has an interlock function. 
     A general outline of the film forming step is as follows. 
     Air pressure inside the chamber  310  in which the mother glass plate  111  is carried in is reduced to approximately 2.5 to 3.5 Torr, for example, and the mother glass plate  111  is heated to a temperature of approximately 200 to 400 degrees centigrade. In this state, the source gas is led into the chamber  310  through an inlet hole  321  that is formed in the center of the shower plate  320 . If the dielectric layer made of silicon dioxide is formed, silane gas (SiH 4 ) and nitrous oxide (N 2 O) are led in as the source gas, for example. The source gas spouts from the shower plate  310  toward the entire of the mother glass plate  111  substantially uniformly. 
     Concomitantly with leading the source gas, air in the chamber  310  is exhausted through a main outlet hole  311  that is located below the movable base  330 . The chamber  310  is provided with a vacuum meter (not shown), and a valve of an exhaust system is controlled in accordance with an output signal of the vacuum meter so that a degree of vacuum inside the chamber  310  can be maintained at a constant value. 
     Thus, the inside of the chamber  310  is supplied with a constant quantity of source gas, and the plasma generated by a high frequency electric power of 1.5 to 2.5 kW activates the source gas so as to promote the chemical reaction. Then, film material generated by the chemical reaction is deposited on the film forming surface S 1  of the mother glass plate  111  so that the dielectric layer is formed. The film forming surface S 1  in this example is the upper face of the mother glass plate  111  on which the display electrode group  40  is formed. Strictly speaking, it includes the exposed surface of the display electrode group  40  and the surface of the substrate between the electrodes. 
     In this film forming process, the masks  71  and  72  are disposed proximately to terminal parts  40   t  of the display electrode group  40  so as to be separated from the terminal parts  40   t  and to be opposed to the same as shown in  FIGS. 7(A) and 7(B) . Although only the mask  71  is shown in  FIGS. 7(A) and 7(B) , the mask  72  is also disposed proximately to terminal parts (not shown) of the display electrode group  40  in the same manner as the mask  71 . However, the terminal parts  40   t  to which the mask  71  is opposed corresponds to the region S 11  shown in  FIG. 3  while the terminal parts to which the mask  72  is opposed corresponds to the region S 12 . 
     When the film forming process is started, as shown in  FIG. 7(A) , a set value of a distance d between the mask  71  and the terminal parts  40   t  of the display electrode group  40  is approximately 0.5 to 2.0 mm. The value of the distance d is sufficiently small compared with the distance D between the mother glass plate  111  and the shower plate  320 . Therefore, a deposition rate of the chemical vapor deposition on the terminal parts  40   t  is extremely smaller than a deposition rate thereof on the parts of the display electrode group  40  that is not covered by the mask  71 . For example, the former rate is one tenth or lower of the latter rate. Therefore, as to the dielectric layer  17  thus formed as shown in  FIG. 7(B) , a thickness t 2  of the part covering the terminal parts  40   t  is extremely smaller than a thickness t 1  of the other parts. Note that the thickness of the dielectric layer  17  is exaggerated in  FIGS. 7(A) and 7(B) . The actual thickness t 1  of the dielectric layer  17  is approximately 5 to 20 microns, which is much smaller than the distance d. The thickness t 2  is a further small value. 
     Since the masks  71  and  72  for the masking process do not touch the display electrode groups  40  in the film forming process, the display electrode groups  40  are not damaged. Since the terminal parts  40   t  are coated by the thin dielectric layer, the display electrode group  40  is not oxidized even if the mother glass plate  111  is exposed to the air or a heat treatment carried out in the air after the film forming process. 
     After forming the dielectric layer  17  having a single layer that is partially thin in this way, magnesia is deposited as the protection film  18 , for example. On this occasion, it is possible to mask a region where the deposition is unnecessary, in addition to the display region. After the protection film  18  is formed, the mother glass plate  111  is divided into a plurality of front plates  10 . The front plate  10  and the rear plate  20  that is manufactured separately are put together and are combined to be a one unit. After they are combined, the thin dielectric layer covering the terminal parts  40   t  of the display electrode group  40  on the front plate  10  is removed by the etching process or the sanding process if necessary. If the insulator covering the terminal parts  40   t  is sufficiently thin, e.g., if its thickness is a few thousand angstroms or smaller, external conductors of a flexible printed circuit board or the like can break the thin insulator so as to make electric contacts with the terminal parts  40   t  by pressing the external conductors onto the terminal parts  40   t . In this case, the process for removing the thin dielectric layer covering the terminal parts  40   t  can be omitted. 
       FIG. 8  is a cross sectional view showing a first example of a panel structure according to the present invention. A panel  10   a  shown in  FIG. 8  is the mother glass plate  111  at the stage when the film formation of the dielectric layer  17  made of a single layer is finished in the manufacturing process of the plasma display panel  1 , and it is a work piece of the front plate  10 . 
     In the panel  10   a , the display electrode group  40  extends from the display region S 60  corresponding to the screen of the mother glass plate  111  to its periphery that is a non-display region S 61 , so it includes the terminal parts  40   t  located in the non-display region S 61 . In addition, the dielectric layer  17  covers the part of the display electrode group  40  in the display region S 60  and the terminal parts  40   t . The thickness t 2  of the part of the dielectric layer  17  covering the terminal parts  40   t  is one tenth or smaller of the thickness t 1  of the part thereof covering the part located in the display region S 60 . 
       FIG. 9  is a cross sectional view showing a second example of the panel structure according to the present invention. A panel  10   b  shown in  FIG. 9  is the mother glass plate  111  at the stage when the film formation of the protection film  18  on the dielectric layer  17  is finished in the manufacturing process of the plasma display panel  1 , and it is a work piece of the front plate  10 . 
     In the illustrated panel  10   b , the protection film  18  is formed so as to cover the entire of the dielectric layer  17  made of a single layer at a uniform thickness. As to a thickness of the insulator (a laminate of the dielectric layer  17  and the protection film  18 ) that covers the display electrode group  40 , a thickness t 4  of the part that covers the terminal parts  40   t  is one tenth or smaller of a thickness t 3  of the part within the display region S 60 . 
     When the panel  10   a  or the panel  10   b  is used for manufacturing the plasma display panel  1 , the terminal parts  40   t  are not damaged when the dielectric layer  17  is formed as described above, so that a break or a continuity defect of an electrode hardly occurs. Since the terminal parts  40   t  are not covered by a thick insulator like that in the display region S 60 , the terminal parts  40   t  can be exposed fast or exposed by pressing the external conductors for electric connection. In other words, the yields can be improved while the production time can be reduced. 
     In the embodiment of the present invention, the mask pattern should be selected in accordance with a shape of an object on which the film should be formed, so it is not limited to the pattern shown in  FIG. 4 . Without limiting to “two in one”, the present invention can be applied to “one in one” in which a single glass substrate is obtained from the mother glass plate, or “n in one” in which n (three or more) glass substrates are obtained from the mother glass plate. 
     The panel according to the present invention includes the illustrated panel  10   a  or  10   b , and the front plate (or the rear plate) corresponding to each plasma display panel obtained by dividing the panel  10   a  or  10   b.    
     The materials of the masks  71  and  72  and the frame  73 , the sizes thereof in a plan view, the thickness thereof, the value of the gap d between the mask  71  or  72  and the electrodes, the number of the masks  71  and  72  as well as the arrangement thereof, the structure of the film forming device and the like can be selected appropriately within a scope of the present invention in accordance with the spirit thereof. 
     INDUSTRIAL APPLICABILITY 
     The present invention is useful for forming an electrode coating film by a chemical vapor deposition process, and it can be used for manufacturing a flat panel display including a plasma display panel or a liquid crystal panel.