1. Field of the Invention
The present invention relates to a covered-type gate valve assembly, and more particularly, to a covered-type gate valve assembly for opening or closing a vacuum chamber.
2. Description of the Prior Art
Generally, a gate valve assembly is widely applied on various kinds, of equipment, such as a stop valve used in water conduits, a discharge valve used in motorcycle's engines, and so on. Additionally, the gate valve assembly is also usually used in semiconductor apparatuses such as an etcher and a chemical vapor deposition apparatus.
Please refer to FIG. 1. FIG. 1 is a schematic diagram of a chemical vapor deposition (CVD) apparatus. As shown in FIG. 1, a CVD apparatus 10 comprises two load chambers 12 for carrying a wafer in or out of the CVD apparatus 10, a substrate-transferring chamber 14, and four reaction chambers 16 for performing a chemical vapor deposition process on the wafer, such as depositing a dielectric layer on the wafer. Additionally, the substrate-transferring chamber 14 functions as a buffer space for allowing the wafer to be transferred from one chamber to the other. Furthermore, the substrate-transferring chamber 14 includes a substrate-transferring device 18 at least comprising a robot and a stage for transferring the wafer.
The CVD apparatus 10 further comprises a plurality of gate valve assemblies 20. Each gate valve assembly 20 is located between each of the load chambers 12 and the substrate-transferring chamber 14, and between each of the reaction chambers 16 and the substrate-transferring chamber 14. Furthermore, each gate valve assembly 20 functions to open or close the chambers. Noticeably, the pressure of the substrate-transferring chamber 14 or each of the reaction chambers 16 is extremely low, and further, is close to a vacuum. Therefore, each gate valve assembly 20 must be provided with an excellent airtightness so as to maintain a vacuum level of each chamber.
Please refer to FIG. 2 to FIG. 5. FIG. 2 is a schematic diagram of a prior art gate valve assembly. FIG. 3 is a cross-sectional view along line 3—3 of FIG. 2. FIG. 4 is a perspective view of the gate valve assembly shown in FIG. 2. FIG. 5 is a cross-sectional view along line 5—5 of FIG. 4. As shown in FIG. 2, a gate valve assembly 20 comprises a valve seat 22 and a valve 30. Additionally, the valve seat 22 comprises a passage opening 24 for allowing the wafer to pass in and out of each chamber, and a plurality of metal sheets 28 located on the bottom of the passage opening 24.
Referring to FIG. 3, the valve 30 comprises a first surface 30a facing the passage opening 24 and a second surface 30b. Moreover, as shown in FIG. 4, the valve 30 comprises a groove 32 surrounding a rim of the first surface 30a, and an O-ring 34 positioned in the groove 32. As shown in FIG. 5, the O-ring 34 has an approximately round cross-section so that the O-ring 34 frequently drops from the groove 32. Accordingly, for tightly fixing the O-ring 34 in the groove 32, the valve 30 further includes polymer glue 36 for filling a gap between the O-ring 34 and sidewalls of the groove 32.
Referring to FIG. 3, the operation manner will be explained as follows. As shown in FIG. 3, a double arrow AA″ indicates a sliding direction along which the valve 30 slides. Furthermore, the passage opening 24 can be closed when the valve 30 slides downward, and after the passage opening 24 is closed, the O-ring 34 of the valve 30 is contacted with a plane 26 of the valve seat 22 for sealing the passage opening 24. On the contrary, when the valve 30 slides upward, the passage opening 24 is opened to make the wafer pass through the passage opening 24. Nevertheless, when the valve 30 slides upward or downward, the second surface 30b will rub against a side surface 28a of each metal sheet 28 frequently, which leads to producing particles. Since the gate valve assembly 20 is installed in the CVD apparatus 10, the produced particles will contaminate the inside of the CVD apparatus 10 and further influence a quality of the semiconductor process. Additionally, the polymer glue 36 is always corroded by a corrosive gas used in a CVD process, and therefore, the gap between the O-ring 34 and the sidewalls of the groove 32 is exposed. That would cause the valve 30 to be unable to seal the passage opening 24 completely, and thus, a vacuum level of the CVD apparatus 10 cannot be effectively maintained.