Conveyors: power-driven – Conveyor system for moving a specific load as a separate unit – System includes control means responsive to sensing means
Reexamination Certificate
1999-03-31
2001-06-12
Underwood, Donald W. (Department: 3652)
Conveyors: power-driven
Conveyor system for moving a specific load as a separate unit
System includes control means responsive to sensing means
C414S940000, C414S674000, C294S907000, C198S371300, C198S395000
Reexamination Certificate
active
06244422
ABSTRACT:
TECHNICAL FIELD
The present invention broadly relates to apparatus for moving and transporting boats carrying semiconductor devices, such as wafers, and deals more particularly with apparatus for sensing and controlling the tipping motion of a boat during movement thereof.
BACKGROUND OF THE INVENTION
A boat is often used in semiconductor manufacturing processes as a carrier for holding and transporting a plurality of semiconductor devices, such as wafers. The boats are transported using various types of specialized handling equipment, such that an entire batch of wafers carried on a boat is processed at the same time. One particular set of handling equipment is employed to move a boat between a standby or transfer position, to a loading position from which equipment, through a series of mechanized movements, transports the boat into a processing station, such as a furnace, for example, where a diffusion operation is performed. Following the simultaneous processing of all the wafers carried on a given boat in a single batch processing operation, the boat is withdrawn in a reverse set of movements by the handling equipment to a transfer station where the boat is transported by other transport mechanisms to another processing station.
The boat handling equipment referred to above typically comprises a boat transfer unit, a boat elevator, a boat clamp and a boat inserter controller. The boat transfer unit, which includes a transfer arm on which the boat sits, transfers the boat from the wafer transfer position, to the loading position vertically aligned above the boat elevator. The boat elevator moves upwardly to contact and engage the boat, whereupon the boat is clamped to the elevator which then moves the boat upwardly into a process chamber. The boat transfer arm typically includes a series of stops and alignment pins which help locate and stabilize the boat on the arm, however the boat is not securely clamped to the arm, and thus is subject to tipping as a result of numerous influences such as vibrations or jolting caused by the equipment or by events such as earth tremors.
Since the boat transfer sequence, like most operations during the fabrication process, is carried out completely automatically by computer controlled robotic mechanisms, it has not been possible to detect when a boat has tipped on a transfer arm to any degree. As a result, where tipping forces are severe, the entire boat may tip over during the transfer process, thus resulting in damage to the wafers, equipment down time and related reduction in throughput. Even where forces causing a boat to tip are not severe, the tipping motion may be sufficient to move the boat out of its normal on-axis alignment position on the transfer arm. This slight off-axis tilt of the boat can result in the boat not moving squarely into the process chamber, but rather colliding with the chamber walls or a scavenger cover disposed adjacent one end of the chamber. This collision, again, can result in process interruption requiring human intervention, as well as wafer damage.
It is apparent then that there is a clear need in the art for apparatus for both sensing when a boat has tipped beyond a threshold level requiring attention, as well as for preventing severe tipping or toppling over of a boat on a transfer arm.
SUMMARY OF THE INVENTION
According to one aspect of the invention, apparatus is provided for preventing tipping of a semiconductor boat carried on a moveable transport arm, which comprises fence structure mounted on the arm that extends upwardly from the arm and partially surrounds the boat such that the fence engages the tipping boat and limits tipping movement of the boat. The fence structure includes an arcuate fence mounted above the arm by vertical supports, and several displaceable guard sections which are resiliently mounted so as to absorb shock when engaged by a tipping boat. A plurality of sensors sense the displacement of each of the guard sections, and send signals to a boat transfer mechanism controller when the boat engages one of the guard sections. A second set of motion sensors are mounted on the arm to sense tipping movement of the base of the boat. Finally, a third series of sensors are mounted on a displaceable cover positioned above the boat elevator, and are operative to send tilt detect signals to the controller when the elevator attempts to move an off-axis, tilted boat upwardly into a process chamber.
According to another aspect of the invention, apparatus is provided for controlling the tipping movement of a boat carried on a transport arm comprising sensor means responsive to the tipping movement of the boat for producing an electrical signal indicative of the tipping movement, and control means coupled with the sensor means and responsive to the electrical signal for controlling the operation of the elevator. The sensor means comprises a first set of sensors carried on a fence which limits the movement of the boat, that produce tip detection signals indicating tipping movement of an upper portion of the boat. The sensor means includes a second set of sensors mounted on the transfer arm to sense tipping movement of the bottom of the boat in an opposite direction and are also operative to send tip detection signals to the controller. A third set of sensors mounted above the boat elevator sense engagement of the boat with a scavenger cover when the elevator attempts to move an off-axis, tilted boat into a process chamber.
In their preferred form, the sensors comprise simple limit switches which include displaceable mechanical elements that produce an electrical signal when actuated by the tipping movement of the boat. The controller typically comprises a programmed computer control, such as a PLC which is responsive to any of the sensors to interrupt both transfer and movement operations so as to avoid damage to the boat or wafers.
It is therefore a primary object of the present invention to provide apparatus for sensing and controlling the tipping movement of a semiconductor boat carried on a transfer arm.
Another object of the invention is to provide apparatus as described above which physically limits the tipping motion of the boat on the arm.
Another object of the invention is to provide apparatus as aforementioned which senses tipping motion either a lower or upper portion of the boat, in either of two directions.
A still further object of the invention is to provide apparatus as described above which includes a controller for automatically interrupting the boat transfer process when boat tipping is sensed, thereby to prevent damage to the boat or wafers.
These, and further objects and advantages of the present invention will be made clear or will become apparent during the course of the following description of a preferred embodiment.
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patent: 5123804 (1992-06-01), Ishii et al.
patent: 5293322 (1994-03-01), Yagi et al.
patent: 5415447 (1995-05-01), Moore et al.
Taiwan Semiconductor Manufacturing Company , Ltd.
Tung & Associates
Underwood Donald W.
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