(1) Field of the Invention
The present invention relates to a substrate laminating apparatus and more particularly to a substrate laminating apparatus suitable for assembling a liquid crystal display panel in which substrates to be laminated are held in a vacuum chamber facing each other and laminated with a narrow spacing between them.
(2) Description of the Related Art
The manufacture of liquid crystal display panels includes a process in which two glass substrates with transparent electrodes and thin-film transistor arrays are stuck together with a very small spacing of several micrometers or so between them using an adhesive agent (hereinafter sometimes called sealant) put on a substrate peripheral area (a finished substrate laminate will be hereinafter called a cell) and liquid crystal is sealed into the space thus made.
One existing technique of sealing liquid crystal in this process is as follows: liquid crystal is dropped on one substrate with a closed pattern of sealant drawn thereon without any injection hole and one substrate is positioned over the other substrate in a vacuum chamber and the upper and lower substrates are brought closer to each other and stuck together. Japanese Patent Application Laid-open Publication No. 2001-305563 discloses a technique whereby a preliminary chamber for carrying a substrate into, and out of, the vacuum chamber is provided and a substrate is carried in and out while the vacuum chamber's atmosphere is the same as the preliminary chamber's.
The above conventional technique causes the following bottleneck in efforts to increase productivity: it takes time to change the pressure level in the vacuum chamber from atmospheric to vacuum in order to make the preliminary chamber and the vacuum chamber have the same atmosphere when a substrate is carried in or out. Particularly, when two substrates are carried into the preliminary chamber and then from the preliminary chamber into the laminating chamber, the zone from the preliminary chamber to the laminating chamber must have an atmospheric pressure because the substrates are carried one by one. In the technique disclosed by Japanese Patent Application Laid-open Publication No. 2001-305563, since substrates are placed on rollers for transportation, they may be damaged or generate dust due to a friction caused by their movement on the rollers. Furthermore, in order to hold an upper substrate on a pressure plate in the laminating chamber, the upper substrate is picked up by suction and adsorption means, then held on a table surface by an electrostatic adsorptive force. Since two adsorption means are used, a complicated pressure plate structure is needed; also since the substrate may come off the pressure plate when the suction and adsorption mode is switched to the electrostatic adsorption mode or vice versa, a means for receiving the substrate must be installed.
Therefore, an object of the present invention is to provide a highly productive substrate laminating apparatus which has means to pick up an upper substrate from a robot hand in vacuum reliably and hold it on an upper table surface and thereby performs lamination of substrates with high accuracy quickly.