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.
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 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.
A plasma CVD device of a parallel plate type is suitable for forming a film on a relatively large object such as a substrate of a flat panel display. This type of device includes an upper electrode that also works as a nozzle for spouting source gas uniformly in a wide range and a lower electrode that also works as a bed for supporting the object, so that plasma is generated between the object on the lower electrode and the upper electrode.
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
If a mask is put on the substrate for masking so as to make terminal parts of electrodes be exposed in the manufacturing process of a plasma display panel in which a dielectric layer having a thickness of approximately a few microns to 20 microns is formed by the CVD process on the substrate on which the electrodes are arranged, a thickness of the dielectric layer may be not uniform. More specifically, as shown in
A cause of this local increase of the film thickness may be that a flow of the source gas in the reaction chamber from an inlet hole to an exhaust hole is interfered by the mask resulting in change of a speed of the flow at the end rim of the mask.
Unevenness of the thickness of the dielectric layer may cause a variation of an operational characteristic among cells of the screen. In order that high quality and stable display is performed, it is desirable that the thickness of the dielectric layer be uniform.
However, if the masking is not performed, the dielectric layer must be removed partially so that terminal parts of the electrodes are exposed after the dielectric is deposited so as to cover the entire of the electrodes. For example, a wet etching process should be performed. Addition of such a process may increase a turnaround time and a cost for manufacturing. In other words, the productivity may be decreased.
It is an object of the present invention to secure uniformity of the film thickness and to improve productivity of the electrode coating by the chemical vapor deposition process.
A method for manufacturing a flat panel display for achieving the object of the present invention includes the steps of forming an electrode group having first and second terminal parts on a substrate, depositing an insulator by the chemical vapor deposition method on the substrate on which the electrode group is formed in the state where one of the first and the second terminal parts is masked that is less affected by the masking than the other terminal part while the other terminal part is not masked, and removing a whole or part of the insulator deposited on the terminal part that is not masked.
The insulator that should be removed after the chemical vapor deposition is less in the case where one of the two terminal parts is masked than in the case where none of them is masked. By a simple consideration, the insulator to be removed in the former case is a half of that in the latter case. Therefore, time and cost necessary for the removing process can be reduced.
If the electrode group includes terminal parts with a common terminal connected to a plurality of electrodes and terminal parts without the same, it is desirable that the terminal parts without the common terminal be masked and the terminal parts with the common terminal be masked. If at least a part of the common terminal is exposed, electric connection of the plurality of electrodes corresponding to the common terminal can be performed. On the contrary, each terminal corresponding to one electrode should be exposed substantially entirely for securing electric connection of the electrode. In other words, the removing process of the insulator should be performed with high accuracy.
Hereinafter, a method of the present invention for manufacturing a plasma display panel as an example of the flat panel display will be described.
A typical plasma display panel has a cell structure as shown in
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, which corresponds to the insulator layer of the present invention. 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
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 is formed by the CVD process, in which either the terminals Xt or the terminals Yt are masked. If the masking is not performed, the entire of the display electrode group 40 including both the terminals Xt and the terminals Yt will be covered with the dielectric layer 17 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 part of the dielectric layer 17 to be removed is decreased so that both the terminals Xt and the terminals Yt can be exposed in a relatively short time so that electric connection of them can be performed.
If four glass substrates are obtained from one mother glass plate (four in one) as an example, the region S11 and the region S12 shown in
In this example, four terminal parts that are close to the center of the mother glass plate 111 out of the total eight terminal parts are not masked while other terminal parts are masked. The masking is performed by using two masks 71 and 72 as shown in
These 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. More specifically, the mask 71 is used for masking the left end parts of the two display electrode groups 40 located on the left side in
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 the “four in one” method, the area of the mother glass plate 111 should be larger than four times the screen (1988 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
The dielectric layer is formed by using the masks 71 and 72 in a plasma CVD device 300 shown in
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 (SiH4) and nitrous oxide (N2O) 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 S1 of the mother glass plate 111 so that the dielectric layer is formed. The film forming surface S1 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 (non-masked surface) of the display electrode group 40 and the surface of the substrate between the electrodes.
In this film forming process, a gas flow is generated when the source gas is led in and air is exhausted. The gas flow is directed from the center to the periphery above the film forming surface S1. Therefore, if the mask is located at the center of the film forming surface S1, the film thickness may be increased locally at the end rims of the mask as described above with reference to
In this example, the mask is not located at the center and its vicinity of the plasma generating space inside the chamber 310 so that uniformity of the film thickness is realized while the masks 71 and 72 are located only at the end part of the plasma generating space for the masking so that a cost necessary for the exposing step of the terminals Xt and Yt can be reduced.
It is desirable to prevent the masks 71 and 72 from touching the display electrode groups 40 in the masking step. It is for preventing damage to the display electrode groups 40. In addition, there is an advantage that the display electrode group 40 will not be 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, because the terminal parts are coated with a thin dielectric layer by the deposition of the gas that enters the gap between the mask 71 or 72 and the display electrode group 40. If the coating layer 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 dielectric layer so as to make electric contacts with the terminal by pressing the external conductors onto the terminal coated with the layer. Therefore, a special process for removing the layer is not necessary. Even if the removing process is necessary, it can be finished in a short time. The masking step in this description is to set the mask to be opposed to the film forming surface S1 so as to make the film thickness be zero or close to zero intentionally, which includes the form of letting the mask touch the film forming surface and the form of preventing the mask from touching the same.
As shown in
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As shown in
The procedure of the manufacturing process, which includes the steps of dividing the mother glass plate 111, combining the front plate 10a and the rear plate 20 to be a single unit, and then removing the dielectric 171, has an advantage as follows. The advantage is that the unnecessary dielectric 171 can be removed by a wet etching process that is advantageous for throughput of the step. In addition, the procedure also has an advantage that oxidation of the electrodes can be prevented by the dielectric 171 in the heat treatment for gluing the rear plate 20 to the front plate 10a.
Hereinafter, variations of the masking step in the chemical vapor deposition process will be described.
When the plasma display panel 1 is connected to a driving circuit, the region S12 and the region S13 shown in
The feature of this example is that each of the regions to be exposed at the center of the mother glass plate 111 in the lateral direction or its vicinity is the region S13 corresponding to the common terminal XT. In order to obtain this feature, the display electrode groups 40b are arranged so that the vertical directions of the display electrode groups 40b are opposite to each other between the left side and the right side of the mother glass plate 111 when the four display electrode groups 40b are formed. The vertical directions are shown by hollow arrows in
Similarly to the example described above, in this example, the four terminal parts that are close to the center of the mother glass plate 111 are not masked while the other terminal parts are masked out of the total eight terminal parts that are two terminal parts for each of the four display electrode groups 40b. The masking step is performed by using the two masks 71 and 72 as shown in
Since the terminal parts including the individual terminals Yt are masked while the terminal parts including the common terminals XT are not masked, the unnecessary dielectric 171 covering the electrodes (see
In the embodiments of the present invention, the mask pattern should be selected in accordance with a shape of the object on which the film should be formed, so it is not limited to the exemplified patterns shown in
The materials of the masks 71 and 72 and the frame 73, the dimensions in a plan view thereof, the thickness thereof, the numbers and locations of the masks 71 and 72, 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.
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 and a liquid crystal panel.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP2005/023165 | 12/16/2005 | WO | 00 | 4/4/2008 |