Abstract:
A substrate attaching device ( 3 ) includes a vacuum chamber ( 31 ), a first electrostatic chuck ( 32 ) at least partly set in the vacuum chamber, and further includes a chuck body ( 321 ) with a plurality of gas releasing holes ( 322 ), a working table ( 33 ) stationable below the first electrostatic chuck in the vacuum chamber, a gas supply ( 34 ) communicating with the gas releasing holes, a pump device ( 35 ) communicating with the vacuum chamber, and a sub-vacuum ( 37 ) chamber communicating with both the vacuum chamber and the pump device.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a substrate attaching device and a substrate attaching method, and especially to a device typically used for combining two substrates such as those that form a framework of a liquid crystal display (LCD) cell. 
   2. General Background 
   An LCD cell generally comprises two glass substrates, a peripheral sealant, and a plurality of liquid crystal molecules retained in a space defined between the substrates and the sealant. The sealant is first printed on one of the glass substrates, and is then adhered to the other glass substrate. The substrates and the sealant cooperatively form the space therebetween, and then the liquid crystal molecules are filled into the space. 
   There are generally two methods used for filling the liquid crystal molecules into the space. The first method is to fill the liquid crystal molecules through filling ports. This method comprises the following steps: firstly, printing a sealant on a first glass substrate, wherein the sealant is rectangular and has one or more gaps that function as filling ports; secondly, combining a second glass substrate with the first glass substrate and curing the sealant, wherein a space is enclosed by the sealant and the two glass substrates; thirdly, immersing the filling ports in a liquid crystal material in a vacuum chamber; and finally, introducing gas into the vacuum chamber to make the liquid crystal molecules fill up the space. 
   The second method is the so-called one-drop-fill (ODF) method. This method comprises the following steps: firstly, printing a sealant on a first glass substrate, wherein the sealant is rectangular and continuous, and a space is enclosed by the sealant and the first glass substrate; secondly, putting liquid crystal molecules into the space drop by drop using a dispenser; and finally, combining a second glass substrate with the first glass substrate and curing the sealant. The ODF process also needs to be performed in a vacuum, at least at the time when the substrates are combined. Thus, in both the first and second methods, a substrate attaching device that can provide a vacuum is necessary. 
   A typical substrate attaching device utilizes an electrostatic chuck (ESC) and a working table. A first substrate is attached to the ESC by way of electrostatic attraction produced by a voltage applied on the ESC. A second substrate is placed on the working table. The ESC and the working table are moved toward each other until the first substrate is attached to the second substrate. Then the applied voltage is stopped, so that the ESC no longer attracts the first substrate. However, electrostatic charges tend to accumulate on the ESC, and these charges do not immediately dissipate when the applied voltage is stopped. That is, the electrostatic attraction between the first substrate and the ESC does not immediately cease, and it may be difficult to disengage the first substrate from the ESC. 
   Referring to  FIG. 4 , this shows another typical substrate attaching device  1 . The substrate attaching device  1  comprises a vacuum chamber  11 , a first ESC  12 , a working table  13 , a gas supply  14 , a vacuum pump  15 , and a controller  16 . The first ESC  12  is set substantially in the vacuum chamber  11 , and the working table  13  can be set in the vacuum chamber  11 . The first ESC  12  comprises a chuck body  121  with a plurality of gas releasing holes  122 . The gas releasing holes  122  communicate with a gas pipe  141 , so that nitrogen gas can be transferred from the gas supply  14  to a bottom surface of the chuck body  121 . A valve  142  is set along the gas pipe  141 , to open and close and thereby regulate the flow of nitrogen gas. The vacuum chamber  11  is connected with the vacuum pump  15  through a gas pipe  151 . A valve  152  is set along the gas pipe  151 , to open and close and thereby regulate the flow of gases. The controller  16  controls the gas supply  14  and the vacuum pump  15  to operate at different times, to feed nitrogen gas and evacuate the inside of the vacuum chamber  11  alternately. 
   In operation, a substrate attaching method using the substrate attaching device  1  comprises the following steps. Firstly, a second substrate  23  is placed on a working table  13 . A sealant  231  is printed on the second substrate  23 , and liquid crystal material  232  material is dropped onto the second substrate  23  in a space defined by the sealant  231 . Secondly, a first substrate  22  is attached to the chuck body  121  by electrostatic attraction. Thirdly, the first substrate  22  and the second substrate  23  are aligned with each other, and the vacuum pump  15  is operated by the controller  16  to evacuate the vacuum chamber  11 . The first ESC  12  is lowered toward the working table  13 , so that the first substrate  22  is attached onto the second substrate  23 . Finally, referring to  FIG. 5 , the vacuum pump  15  is stopped by the controller  16 . Nitrogen gas is and supplied to the bottom surface of the chuck body  121  by the gas supply  14  under the control of the controller  16 . The flowing nitrogen gas can help separate the first substrate  22  from the chuck body  121 , so that the combined first and second substrates  22 ,  23  can be moved out from the vacuum chamber  11 . 
   However, when the gas supply  14  supplies nitrogen gas to the chuck body  121 , the vacuum pump of the vacuum chamber  11  stops operating. Thus, a pressure in an inside space of the combined substrates  22 ,  23  is lower than a pressure in the vacuum chamber  11 . Under such conditions, the nitrogen gas may penetrate into the inside space of the combined substrates  22 ,  23 . Bubbles of nitrogen gas may form in the liquid crystal material  232 . These can result in impaired performance or even failure of the LCD cell. 
   What is needed, therefore, is a substrate attaching device that can improve a manufacturing yield of LCD cells. What is also needed is a substrate attaching method that can improve a manufacturing yield of LCD cells. 
   SUMMARY 
   In one preferred embodiment, a substrate attaching device comprises a vacuum chamber, a first electrostatic chuck at least partly set in the vacuum chamber, and comprises a chuck body with a plurality of gas releasing holes, a working table stationable below the first electrostatic chuck in the vacuum chamber, a gas supply communicating with the gas releasing holes, a pump device communicating with the vacuum chamber, and a sub-vacuum chamber communicating with both the vacuum chamber and the pump device. 
   In another preferred embodiment, a method for reliably attaching two substrates together comprises: providing a substrate attaching device comprising a vacuum chamber, a first electrostatic chuck at least partly set in the vacuum chamber, a working table stationable below the first electrostatic chuck in the vacuum chamber, and a sub-vacuum chamber connected with the vacuum chamber; holding a first one of the substrates to the first electrostatic chuck, and disposing a second one of the substrates on the working table; moving the first electrostatic chuck and the working table closer together until the first substrate and the second substrate are attached together; and supplying a gas to the first electrostatic chuck in order to separate the first substrate from the first electrostatic chuck, while simultaneously maintaining a degree of vacuum in the sub-vacuum chamber higher than a degree of vacuum in the vacuum chamber. 
   The nitrogen gas cannot penetrate into the space inside the combined substrates, accordingly, the yield of LCD cells comprising the combined substrates is improved. 
   Other advantages and novel features will become more apparent from the following detailed description of preferred embodiments when taken in conjunction with the accompanying drawings, in which: 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic, side cross-sectional view of a substrate attaching device according to a preferred embodiment of the present invention, together with a pair of substrates inside a vacuum chamber of the substrate attaching device; 
       FIG. 2  is similar to  FIG. 1 , but showing gas flow during a step in a method for attaching the two substrates together according to a preferred embodiment of the present invention; 
       FIG. 3  is similar to  FIG. 2 , but showing a subsequent step in the method for attaching the two substrates together, including gas flow during such subsequent step; 
       FIG. 4  is a schematic, side cross-sectional view of a typical substrate attaching device, together with a pair of substrates inside a vacuum chamber of the substrate attaching device; and 
       FIG. 5  is a similar to  FIG. 4 , but showing a step in a method for attaching the two substrates together by using the substrate attaching device. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Reference will now be made to the drawings to describe the preferred embodiments in detail. 
   Referring to  FIG. 1 , a substrate attaching device  3  in accordance with the preferred embodiment comprises a vacuum chamber  31 , a first ESC  32 , a working table  33 , a gas supply  34 , a vacuum pump  35 , a controller  36 , and a sub-vacuum chamber  37 . The controller  36  controls the gas supply  34  and the vacuum pump  35  to operate at different times alternately. 
   The vacuum chamber  31  is connected with the vacuum pump  35 , which is used to evacuate an inside of the vacuum chamber  31  to a pressure of about 0.1 torr. Thus, the vacuum chamber  31  can provide a vacuum condition. The vacuum pump  35  communicates with the vacuum chamber  31  through a second gas pipe  351 , wherein the second gas pipe  351  comprises a valve  352  for regulation the gas flow of the second gas pipe  351  by opening or closing. 
   The first ESC  32  is set substantially in the vacuum chamber  31 , and comprises a chuck body  321  with a plurality of gas releasing holes  322 . The chuck body  321  can attract a first substrate  42  by electrostatic attraction. The first ESC  32  can be raised or lowered relative to the working table  33 . The working table  33  is used to place a second substrate  43  thereon. After the second substrate  43  is placed on the working table  33 , the working table  33  is moved in the vacuum chamber  31  until is directly under the first ESC  32 . That is, the working table  33  can be moved into and out from the vacuum chamber  31 . 
   The gas releasing holes  322  communicate with a first gas pipe  341 , so that nitrogen gas can be transferred from the gas supply  34  to a bottom surface of the chuck body  321 . The first gas pipe  341  comprises a valve  342 , which can be opened or closed to regulate the flow of gas through the first gas pipe  341 . 
   The sub-vacuum chamber  37  communicates with the vacuum chamber  31  through a third gas pipe  371 , and also communicates with the vacuum pump  35  through a fourth gas pipe  373 . The third gas pipe  371  and the fourth gas pipe  373  respectively comprise a valve  372  and a valve  374 , for regulation of the flow of gas through the third gas pipe  371  and the fourth gas pipe  373  respectively. 
   Referring to  FIG. 2  and  FIG. 3 , in operation, a substrate attaching method using the substrate attaching device  3  comprises the following steps. Firstly, the first substrate  42  is held by the electrostatic chuck body  321 , and the working table  33  is moved out of the vacuum chamber  31 . Secondly, the second substrate  43  is placed on the working table  33 . A sealant  431  is printed on the second substrate  43 . Liquid crystal molecules  432  are dispensed into a space enclosed by the sealant  431  and the second substrate  43 , drop by drop using a dispenser (not shown). Thirdly, the working table  33  is moved into the vacuum chamber  31 , and the working table  33  is aligned with the electrostatic chuck body  321 . Fourthly, the valve  342  is closed, and the valves  352 ,  372  and  374  are opened. The controller  36  controls the vacuum pump  35  to evacuate gas from inside the vacuum chamber  31 , with a direction of gas flow as shown in  FIG. 2 . Fifthly, the valves  352  and  372  are closed, and the valve  374  is opened. The vacuum pump  35  continues to evacuate gas from inside the sub-vacuum chamber  37 , in order to make the degree of vacuum of the sub-vacuum chamber  37  higher than the degree of vacuum of the vacuum chamber  31 . Sixthly, referring to  FIG. 3 , the first ESC  32  is moved toward the working table  33 , so that the first substrate  42  and the second substrate  43  are attached to each other. Finally, the controller  36  is stopped. The valve  342  is opened, so that nitrogen gas is supplied from the gas supply  34  to the first substrate  42 . The nitrogen gas may be supplied at a constant flow rate, or at a varying flow rate such as in pulses. The nitrogen gas facilitates separation of the first substrate  42  from the chuck body  321 . Thus the combined first and second substrates  42 ,  43  supported on the working table  33  can be readily moved out from the vacuum chamber  31 . 
   The gas supply  34  feeds nitrogen gas under pressure to the first substrate  42  in the vacuum chamber  31 , with the valves  352  and  374  being closed and the valve  372  being open. Because the degree of vacuum of the sub-vacuum chamber  37  is higher than the degree of vacuum of the vacuum chamber  31 , the nitrogen gas subsequently flows into the sub-vacuum chamber  37  without affecting the degree of vacuum of the vacuum chamber  31 . Thus, the pressure in the space inside the combined substrates  42 ,  43  is equal to the pressure in the vacuum chamber  31 . Under such conditions, the nitrogen gas cannot penetrate into the space inside the combined substrates  42 ,  43 . Accordingly, the yield of LCD cells comprising the combined substrates  42 ,  43  is improved. 
   In alternative embodiments, the working table  33  can also be a chuck body, so as to attract the second substrate  43  by electrostatic attraction. Any of the first, second, third, and fourth gas pipes  341 ,  351 ,  371 ,  373  can be gas pipelines or piping systems suitable for particular applications. 
   It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.