Material or article handling – Apparatus for moving material between zones having different...
Reexamination Certificate
1999-06-15
2001-07-03
Bratlie, Steven A. (Department: 3652)
Material or article handling
Apparatus for moving material between zones having different...
C414S939000
Reexamination Certificate
active
06254328
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a load lock unit for transferring a cassette of semiconductor wafers between regions having different pressures or environments and a method for transferring the wafer cassette through the load lock unit. More particularly, the invention relates to a dual stage wafer load lock unit wherein first and second chambers of the load lock are selectively separated by a platform carrying the wafer cassette, and a method of transferring wafers in a cassette through the dual stage load lock.
Semiconductor wafer processing typically occurs within high vacuum process chambers which are separated from adjacent chambers and/or external conditions (ambient or atmospheric pressure) by valved openings. Typically, a central transfer chamber is provided with a transfer robot located therein for transferring wafers between a load lock chamber and one or more process chambers located about the periphery of the transfer chamber. The load lock chamber is also provided for transferring wafers between the transfer chamber, which is typically at high vacuum, and the outside, typically a clean room at atmospheric pressure.
One well known prior art system for loading wafers into a process system employs a wafer cassette, having a plurality of individual slots therein, within which individual wafers may be placed or removed. This cassette is placed onto a moveable floor or platform in the load lock chamber, and an elevator mechanism moves the floor in increments to sequentially place, or index, individual slots of the cassette into registration with a robot blade which is used to selectively remove wafers from the cassette or place wafers therein. A slit valve, located in alignment with the robot blade, isolates the load lock chamber from the robot/transfer chamber. To enable access of the robot to all of the slots in the cassette, the cassette must be moveable, within the load lock, to align the wafer slots at each end of the cassette with the robot blade. As a result, the volume of the load lock chamber must be approximately at least twice the volume of the cassette, to create the clearance needed to move the cassette the entire travel length required to access each wafer slot in the cassette with the robot while maintaining the cassette within the controlled environment of the load lock.
To avoid a backflow of ambient air into the transfer chamber, when the valve between the two chambers is opened to transfer a wafer, it is essential that the load lock chamber be maintainable at a pressure substantially equal to the high vacuum of the transfer chamber. Thus, because of the need to have a load lock volume significantly exceeding that of the cassette to enable cassette movement, and thereby robot blade access to each wafer slot in the cassette, a large dead space equal to the required cassette clearance space must be pumped down to vacuum each time a cassette is replaced in the load lock or the load lock door is opened. Additionally, exposing the interior surfaces of the load lock chamber to atmosphere by opening of the load lock door for cassette loading or unloading allows water vapor and contaminants to enter the load lock chamber and adhere thereto.
Accordingly, there is a need in the art for a load lock chamber which provides cassette to wafer indexing while minimizing the volume and space of the load lock which is exposed to ambient conditions.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, there is provided a load lock apparatus for transferring an article between a first environment at substantially atmospheric pressure and a high vacuum processing system. The apparatus includes a first chamber having an environment which is adjustable between substantially atmospheric pressure and high vacuum and a second chamber having an environment which is maintained in high vacuum. In one aspect of the invention, the second chamber is in selective communication with the vacuum processing system and the first chamber. In another embodiment the first chamber is in selective communication with the vacuum processing system. In another aspect of the invention, the second chamber is used as clearance volume or space maintained at vacuum, and the access to the high vacuum processing system is provided through the first chamber. Also provided is a means for selectively separating the first chamber environment from the second chamber environment. Thus, as a cassette is loaded into the load lock, only the first chamber need be exposed to atmosphere, thereby reducing the surface area of the load lock exposed to water vapor and contaminants, and reducing the volume of the load lock which must be pumped to vacuum. The second chamber, which provides clearance space for movement of the cassette to enable robot access to each wafer slot in the cassette, need only be exposed to the first chamber after the first chamber has been evacuated, and then only when the cassette needs to be positioned to enable access of a robot blade thereto. The environment within the second load lock chamber is preferably maintained at a pressure equal or substantially equal to that maintained in the process chamber environment, such as that in the transfer chamber, and may be configured without an isolation valve between the second chamber and the vacuum processing system.
In one aspect, the selective separating means preferably includes a movable pedestal upon which the article is carried, a dividing ledge extending a distance inwardly from an inner wall of the apparatus and located between the first and second chambers, and means for sealing the movable pedestal against the dividing ledge when the apparatus is in a loading position. Preferably, an O-ring seal is provided on an upper surface of the pedestal to sealingly engage a lower surface of the dividing ledge when the pedestal is raised to the loading position. The apparatus may further include means for removably connecting together the first chamber, dividing ledge and second chamber.
An article conditioning means may also be provided within the load lock for performing pre-processing and post-processing operations, and preferably includes a movable sub-chamber located within the first load lock chamber. The sub-chamber may exhibit an opening at the side facing the selective separating means between the first chamber and the second chamber. The article conditioning means may include means for heating the area within said movable sub-chamber, the heating means including means for introducing a heated gas into the movable sub-chamber and/or a resistance heating element thermally coupled to the movable sub-chamber. The article conditioning means may also include means for post-process wafer cooling, preferably by introduction of a cooled gas into the movable sub-chamber.
Drive means, may be provided for moving the sub-chamber between an open position and a closed position. Sealing means may also be included to seal the lower surface of the sub-chamber against the dividing ledge when the sub-chamber is in the closed position. The sealing means may include an O-ring seal located on a lower surface of the sub-chamber, to sealingly engage an upper surface of the dividing ledge when the sub-chamber is in the closed position.
A further aspect of the invention is a method for transferring an article between a first environment at substantially atmospheric pressure and a second environment at high vacuum. The article is transferred through a load lock chamber having selectively separable first and second chambers, wherein the second load lock chamber is maintained at high vacuum substantially equal to the high vacuum of the second environment.
According to one preferred embodiment, a method for loading an article, such as a semiconductor wafer cassette carrying one or more semiconductor wafer substrates, into a processing system is provided. First the article is transferred from the atmospheric environment onto a platform in the first load lock chamber while the first load lock chamber is at substantially
Applied Materials Inc.
Bratlie Steven A.
Fulbright & Jaworski LLP
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